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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Fisher cassette heads
The heads from left to right are, the erase head, the record head and the
playback head. Any cassette I've ever seen has a guide attached to the playback head. If possible, bend the damaged guide back into place. Usually this guide is spot welded, therefore the height of the guide might not have changed. This guide sets the tracking which usually is not adjustable because the guide is fixed to the playback head at the factory. On rare occasions this guide is adjustable. The tilt of the head sets azimuth which is adjustable on all decks. You will have to examine the record and playback heads to see if there is azimuth adjustments for both heads. I would expect there is. Head height raises or lowers the position of the head gaps on the tape. Azimuth rotates the gaps so that they are aligned perpendicular (90 degrees) to the tape. Azimuth will have a slight effect on the head height. Another head adjustment you might have is zenith. Usually located at the rear of the head, it tilts the face of the head, so that the head is parallel to the tape. This adjustment if incorrect, would tilt the top of the head either closer or further from the tape than the bottom of the head. It causes uneven head wear and it causes the tape to scew up and down. As the tape scews, the azimuth and tracking will also be out of adjustment. The erase head should also have a non adjustable guide affixed to it. Check to see that you have these guides in place, the azimuth and zenith adjustments, and that the adjustments will move the heads. If you can't physically align the heads, or the guides are bad, there is no sense in going any further. you will have to replace whatever mechanics are bad. You might want to sacrafice an old cassette by cutting away the plastic shell in the area where the heads contact the tape. This will give you the abiltiy to see how the tape rides over the heads. If the tape is visibly moving up or down, you will have to correct this. It is impossible to align a head to tape that moves all over the place. The basic concept is to set all guides at the same height so that the tape enters the shell and leaves the shell at the same height. Any guides in between should not raise or lower the tape as it travels thru the shell. Post back here with your results and we'll determine the next step. bg Marko wrote in message ... BG: I thought I would check for replies just one more time before I stopped NG activity for awhile. Glad I did. I have a signal generator, alignment tape, scope, and HP5210 freq meter that I have used to set the motor RPM with 1KHz test tone. I haven't checked yet, but I am hoping that (1) the head on the far right is the play head (2) the tape monitor switch will allow me to record a test tone (I will use 10KHz) and then monitor it with the play head so that I can align the record head. (3) that the tape guide on the PB head (which has been bent out of the tape path) is not necessary for proper tape transfer over the heads. What worries me is that the tape guide is on the record head and I must align the playback head first. I didn't notice the third head at first and aligned the playback with the record head adjustment screw. This worked because the tape guide is on the record head. How do I start out with proper alignment of the two tape guides before aligning the heads? One guide, the first one, is affixed to the transport frame and the second guide is affixed to the record head. I think this problem may have been encountered by whoever worked on it before it was sent to a resale shop. I could see that they had disturbed the paint on the screws. It also had two stretched belts and a very dirty rec/play switch on the board, so I'm not sure. The belts may have stretched and the grease in the switch may have dried from sitting on the shelf for years after they encountered the alignment problem. What do you suggest? Sincerely, Mark (this is a top post) ----- Original Message ----- From: "bg" Newsgroups: sci.electronics.repair Sent: Sunday, July 27, 2003 11:46 PM Subject: Fisher cassette heads You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark "bg" wrote in message ... You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark |
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Fisher cassette heads
BG: I have reread your post several times and now realize that without the
guide on the PB head then it is up to me and luck to get it going right. Unless you have some more advice, thanks much, you've been a great help. Sincerely, Mark "bg" wrote in message ... The heads from left to right are, the erase head, the record head and the playback head. Any cassette I've ever seen has a guide attached to the playback head. If possible, bend the damaged guide back into place. Usually this guide is spot welded, therefore the height of the guide might not have changed. This guide sets the tracking which usually is not adjustable because the guide is fixed to the playback head at the factory. On rare occasions this guide is adjustable. The tilt of the head sets azimuth which is adjustable on all decks. You will have to examine the record and playback heads to see if there is azimuth adjustments for both heads. I would expect there is. Head height raises or lowers the position of the head gaps on the tape. Azimuth rotates the gaps so that they are aligned perpendicular (90 degrees) to the tape. Azimuth will have a slight effect on the head height. Another head adjustment you might have is zenith. Usually located at the rear of the head, it tilts the face of the head, so that the head is parallel to the tape. This adjustment if incorrect, would tilt the top of the head either closer or further from the tape than the bottom of the head. It causes uneven head wear and it causes the tape to scew up and down. As the tape scews, the azimuth and tracking will also be out of adjustment. The erase head should also have a non adjustable guide affixed to it. Check to see that you have these guides in place, the azimuth and zenith adjustments, and that the adjustments will move the heads. If you can't physically align the heads, or the guides are bad, there is no sense in going any further. you will have to replace whatever mechanics are bad. You might want to sacrafice an old cassette by cutting away the plastic shell in the area where the heads contact the tape. This will give you the abiltiy to see how the tape rides over the heads. If the tape is visibly moving up or down, you will have to correct this. It is impossible to align a head to tape that moves all over the place. The basic concept is to set all guides at the same height so that the tape enters the shell and leaves the shell at the same height. Any guides in between should not raise or lower the tape as it travels thru the shell. Post back here with your results and we'll determine the next step. bg Marko wrote in message ... BG: I thought I would check for replies just one more time before I stopped NG activity for awhile. Glad I did. I have a signal generator, alignment tape, scope, and HP5210 freq meter that I have used to set the motor RPM with 1KHz test tone. I haven't checked yet, but I am hoping that (1) the head on the far right is the play head (2) the tape monitor switch will allow me to record a test tone (I will use 10KHz) and then monitor it with the play head so that I can align the record head. (3) that the tape guide on the PB head (which has been bent out of the tape path) is not necessary for proper tape transfer over the heads. What worries me is that the tape guide is on the record head and I must align the playback head first. I didn't notice the third head at first and aligned the playback with the record head adjustment screw. This worked because the tape guide is on the record head. How do I start out with proper alignment of the two tape guides before aligning the heads? One guide, the first one, is affixed to the transport frame and the second guide is affixed to the record head. I think this problem may have been encountered by whoever worked on it before it was sent to a resale shop. I could see that they had disturbed the paint on the screws. It also had two stretched belts and a very dirty rec/play switch on the board, so I'm not sure. The belts may have stretched and the grease in the switch may have dried from sitting on the shelf for years after they encountered the alignment problem. What do you suggest? Sincerely, Mark (this is a top post) ----- Original Message ----- From: "bg" Newsgroups: sci.electronics.repair Sent: Sunday, July 27, 2003 11:46 PM Subject: Fisher cassette heads You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark "bg" wrote in message ... You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark |
#4
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Fisher cassette heads
BG: OK let's give it a try. This time I will get it right about where the
guides are Originally this machine had four guides: (1) one solidly affixed to left of erase head (2) one on left of record head, but affixed to the transport frame (3) One spot welded to the right side of the record head (4) One affixed (with miniature screw) to left side of PB head The one on the right side of the record head is less than a cm from the guide on the left of the PB head (PB head guide is effectively missing, not repairable, mangled) As far as stability of the tape going across the heads goes, I feel that the 3 remaining guides will be enough, if they are aligned The two problems are as follows: (1) The guide to the left of the record head is affixed to frame and all other guides must correspond to this one or the tape will not ride smoothly on the heads. (2) Seems like the guide to the right of the record head should not effect the path of the tape over the PB head because it is over the screw that is not for adjustment (the mounting screw that is tightened and not adjustable). BUT, it does because I didn't notice the 3rd head when I was adjusting the azimuth for the record head (I thought it was the playback head at the time). Turning the azimuth adjustment for the record head affects the path of the tape over the PB head. I recall seeing the PB amplitude vary on a scope as the azimuth screw for Rec head was turned. I hope I have written this in a readable manner. All I can see is that I should adjust the Rec and PB heads over and over until hopefully they are aligned. Any ideas or warnings, BG? Thanks for your help. Your advice has given me a much needed understanding of this situation. Mark "bg" wrote in message ... Just about every deck I've ever seen has a guide on the ingoing side of the erase head and a guide on the outgoing side of the playback head, with no other guides in between. It is also common practise to affix the guides to the heads, not the chassis. On the chassis there will be posts that hold the shell in place, they are not tape guides. I have plenty of time . If you are ready to continue let me know bg Marko wrote in message ... BG: I have reread your post several times and now realize that without the guide on the PB head then it is up to me and luck to get it going right. Unless you have some more advice, thanks much, you've been a great help. Sincerely, Mark "bg" wrote in message ... The heads from left to right are, the erase head, the record head and the playback head. Any cassette I've ever seen has a guide attached to the playback head. If possible, bend the damaged guide back into place. Usually this guide is spot welded, therefore the height of the guide might not have changed. This guide sets the tracking which usually is not adjustable because the guide is fixed to the playback head at the factory. On rare occasions this guide is adjustable. The tilt of the head sets azimuth which is adjustable on all decks. You will have to examine the record and playback heads to see if there is azimuth adjustments for both heads. I would expect there is. Head height raises or lowers the position of the head gaps on the tape. Azimuth rotates the gaps so that they are aligned perpendicular (90 degrees) to the tape. Azimuth will have a slight effect on the head height. Another head adjustment you might have is zenith. Usually located at the rear of the head, it tilts the face of the head, so that the head is parallel to the tape. This adjustment if incorrect, would tilt the top of the head either closer or further from the tape than the bottom of the head. It causes uneven head wear and it causes the tape to scew up and down. As the tape scews, the azimuth and tracking will also be out of adjustment. The erase head should also have a non adjustable guide affixed to it. Check to see that you have these guides in place, the azimuth and zenith adjustments, and that the adjustments will move the heads. If you can't physically align the heads, or the guides are bad, there is no sense in going any further. you will have to replace whatever mechanics are bad. You might want to sacrafice an old cassette by cutting away the plastic shell in the area where the heads contact the tape. This will give you the abiltiy to see how the tape rides over the heads. If the tape is visibly moving up or down, you will have to correct this. It is impossible to align a head to tape that moves all over the place. The basic concept is to set all guides at the same height so that the tape enters the shell and leaves the shell at the same height. Any guides in between should not raise or lower the tape as it travels thru the shell. Post back here with your results and we'll determine the next step. bg Marko wrote in message ... BG: I thought I would check for replies just one more time before I stopped NG activity for awhile. Glad I did. I have a signal generator, alignment tape, scope, and HP5210 freq meter that I have used to set the motor RPM with 1KHz test tone. I haven't checked yet, but I am hoping that (1) the head on the far right is the play head (2) the tape monitor switch will allow me to record a test tone (I will use 10KHz) and then monitor it with the play head so that I can align the record head. (3) that the tape guide on the PB head (which has been bent out of the tape path) is not necessary for proper tape transfer over the heads. What worries me is that the tape guide is on the record head and I must align the playback head first. I didn't notice the third head at first and aligned the playback with the record head adjustment screw. This worked because the tape guide is on the record head. How do I start out with proper alignment of the two tape guides before aligning the heads? One guide, the first one, is affixed to the transport frame and the second guide is affixed to the record head. I think this problem may have been encountered by whoever worked on it before it was sent to a resale shop. I could see that they had disturbed the paint on the screws. It also had two stretched belts and a very dirty rec/play switch on the board, so I'm not sure. The belts may have stretched and the grease in the switch may have dried from sitting on the shelf for years after they encountered the alignment problem. What do you suggest? Sincerely, Mark (this is a top post) ----- Original Message ----- From: "bg" Newsgroups: sci.electronics.repair Sent: Sunday, July 27, 2003 11:46 PM Subject: Fisher cassette heads You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark "bg" wrote in message ... You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark |
#5
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Fisher cassette heads
It sounds as though you have enough guides to make it work.
Alignment tapes are usually full track. You can't set tracking with it but you can use it for azimuth. Hopefully the fixed guides are in the right position. My gut feel is that the azimuth would be the only adjustment you need to make unless the guides were moved somehow. The normal method for setting the head height is to record a tone on the tape and then measure the track positions with a toolmakers microscope. I'm sure you don't have this equipment, so the next best thing would be to record a 1000 hz tone on a known good cassette deck and use that tape as your tracking standard. As you play the tape back in the Fisher deck, lightly push or lift the playback head to see if the playback level increases. If the guide on your playback head hasn't been moved, your tracking should be OK. Flip the tape over and check the levels again. For every .001 inch that the tracking is off, you lose about .4db of signal level. If the levels are within 1/2 to 1 db from side one, you probably won't be able to improve the tracking by moving the playback head guide. Moving it that small amount would be very difficult, and the guides have to be wider than the tape by about .001 inch to allow the tape to fit thru it anyway. So .001 of tape movement is perfectly normal. To set azimuth on the playback head, use the 10 khz tone on your alignment tape. There's two ways to do this. One way is to simply adjust your playback head azimuth for maximum output at 10 khz. The other method is to measure the phase between the left and right tracks. (lissajous patterns) Set up your scope for X-Y mode. Plug the left line out into one channel and the right line out into the other channel. When the two tracks are in perfect phase alignment, the scope trace should make a line angled at 45 degrees . It looks like this -- (/) . If the phase alignment is out by 180 degrees the line is angled like this ---- (\). Between 0 and 180 degrees the line changes to an oval or a circle. Multiples of 360 degrees will look like it's in phase alignment, but the length of the line will get shorter. So what you want is the longest line possible angled like (/). Note that when the azimuth is off, the level of the 10 khz tone drops off. Lower frequencies are barely affected by bad azimuth, that's why it is set using a higher frequency tone. If the 45 degree line fluctuates rapidly, there is a problem with the tape moving up and down. This might be due to the guides not all being at the same height or bad zenith. Your alignment tape might be stretched also. It doesn't take very much abuse to stretch a tape. If the tape seems to be bad , try recording a 10k tone on a good cassette deck and use that for your alignment tape. Now that the playback head is in correct azimuth and height. You can align your record head to your playback head. Check the height of the record head by recording a 1000 hz tone. Move the record head up or down until you get maximum output from the playback head. Again, if you flip the tape over, the levels should playback within about 1db. seeing as the record head has a guide welded to it , there should be no reason for the record head tracking to be incorrect. Set the azimuth by recording a 10khz tone and adjust the record head azimuth for maximum output from the playback head or 0 degree phase shift between left and right outputs. You might need to set levels, EQ, bias, and calibrate the VU meters. This would be hard to do unless the adjustment pots are marked on the circuit board, but not impossible to figure out. Let me know how you make out. Marko wrote in message ... BG: OK let's give it a try. This time I will get it right about where the guides are Originally this machine had four guides: (1) one solidly affixed to left of erase head (2) one on left of record head, but affixed to the transport frame (3) One spot welded to the right side of the record head (4) One affixed (with miniature screw) to left side of PB head The one on the right side of the record head is less than a cm from the guide on the left of the PB head (PB head guide is effectively missing, not repairable, mangled) As far as stability of the tape going across the heads goes, I feel that the 3 remaining guides will be enough, if they are aligned The two problems are as follows: (1) The guide to the left of the record head is affixed to frame and all other guides must correspond to this one or the tape will not ride smoothly on the heads. (2) Seems like the guide to the right of the record head should not effect the path of the tape over the PB head because it is over the screw that is not for adjustment (the mounting screw that is tightened and not adjustable). BUT, it does because I didn't notice the 3rd head when I was adjusting the azimuth for the record head (I thought it was the playback head at the time). Turning the azimuth adjustment for the record head affects the path of the tape over the PB head. I recall seeing the PB amplitude vary on a scope as the azimuth screw for Rec head was turned. I hope I have written this in a readable manner. All I can see is that I should adjust the Rec and PB heads over and over until hopefully they are aligned. Any ideas or warnings, BG? Thanks for your help. Your advice has given me a much needed understanding of this situation. Mark "bg" wrote in message ... Just about every deck I've ever seen has a guide on the ingoing side of the erase head and a guide on the outgoing side of the playback head, with no other guides in between. It is also common practise to affix the guides to the heads, not the chassis. On the chassis there will be posts that hold the shell in place, they are not tape guides. I have plenty of time . If you are ready to continue let me know bg Marko wrote in message ... BG: I have reread your post several times and now realize that without the guide on the PB head then it is up to me and luck to get it going right. Unless you have some more advice, thanks much, you've been a great help. Sincerely, Mark "bg" wrote in message ... The heads from left to right are, the erase head, the record head and the playback head. Any cassette I've ever seen has a guide attached to the playback head. If possible, bend the damaged guide back into place. Usually this guide is spot welded, therefore the height of the guide might not have changed. This guide sets the tracking which usually is not adjustable because the guide is fixed to the playback head at the factory. On rare occasions this guide is adjustable. The tilt of the head sets azimuth which is adjustable on all decks. You will have to examine the record and playback heads to see if there is azimuth adjustments for both heads. I would expect there is. Head height raises or lowers the position of the head gaps on the tape. Azimuth rotates the gaps so that they are aligned perpendicular (90 degrees) to the tape. Azimuth will have a slight effect on the head height. Another head adjustment you might have is zenith. Usually located at the rear of the head, it tilts the face of the head, so that the head is parallel to the tape. This adjustment if incorrect, would tilt the top of the head either closer or further from the tape than the bottom of the head. It causes uneven head wear and it causes the tape to scew up and down. As the tape scews, the azimuth and tracking will also be out of adjustment. The erase head should also have a non adjustable guide affixed to it. Check to see that you have these guides in place, the azimuth and zenith adjustments, and that the adjustments will move the heads. If you can't physically align the heads, or the guides are bad, there is no sense in going any further. you will have to replace whatever mechanics are bad. You might want to sacrafice an old cassette by cutting away the plastic shell in the area where the heads contact the tape. This will give you the abiltiy to see how the tape rides over the heads. If the tape is visibly moving up or down, you will have to correct this. It is impossible to align a head to tape that moves all over the place. The basic concept is to set all guides at the same height so that the tape enters the shell and leaves the shell at the same height. Any guides in between should not raise or lower the tape as it travels thru the shell. Post back here with your results and we'll determine the next step. bg Marko wrote in message ... BG: I thought I would check for replies just one more time before I stopped NG activity for awhile. Glad I did. I have a signal generator, alignment tape, scope, and HP5210 freq meter that I have used to set the motor RPM with 1KHz test tone. I haven't checked yet, but I am hoping that (1) the head on the far right is the play head (2) the tape monitor switch will allow me to record a test tone (I will use 10KHz) and then monitor it with the play head so that I can align the record head. (3) that the tape guide on the PB head (which has been bent out of the tape path) is not necessary for proper tape transfer over the heads. What worries me is that the tape guide is on the record head and I must align the playback head first. I didn't notice the third head at first and aligned the playback with the record head adjustment screw. This worked because the tape guide is on the record head. How do I start out with proper alignment of the two tape guides before aligning the heads? One guide, the first one, is affixed to the transport frame and the second guide is affixed to the record head. I think this problem may have been encountered by whoever worked on it before it was sent to a resale shop. I could see that they had disturbed the paint on the screws. It also had two stretched belts and a very dirty rec/play switch on the board, so I'm not sure. The belts may have stretched and the grease in the switch may have dried from sitting on the shelf for years after they encountered the alignment problem. What do you suggest? Sincerely, Mark (this is a top post) ----- Original Message ----- From: "bg" Newsgroups: sci.electronics.repair Sent: Sunday, July 27, 2003 11:46 PM Subject: Fisher cassette heads You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark "bg" wrote in message ... You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark |
#6
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Fisher cassette heads
BG: Your post is very well written and I do understand it. Nevertheless, I
will read it several times until I am sure that I have it all understood. I am currently working on something else which may not be finished for several days. You probably visit this NG often so I will post a message for you when I am done. It is not uncommon for something to come along that may delay this for a few weeks. I don't think this deck has a zenith adjustment unless it is the play in the azimuth adjustment. Sounds to me that what makes a low end deck sound "inexpensive" is partially due to the poor alignment of the heads. I have done XY plots before so I follow you on the circles and lines on the CRT. I built a quadraphonic decoder years ago which utilized a broadband all-pass filter, so I was looking at circles with the 90 degree shift. I have also determined that the 10KHz tone on the test tape gives the most accurate adjustment of azimuth. I'll have to think about the statement you made about the test tape being full track. I have been picking up $5 cassette decks and scrapping them if I couldn't get them going. If the tires were melted all over the transport I scrapped them. Sometimes the heads and capstan were so coated with oxide that they were literally ruined from corrosion. I have a Teac and a Technics here that are totally functional, but they don't have good speed accuracy. When I did manage to get belts etc. on it I used the alignment tape to get both channels to record and play strong in the car. I have a bunch of $3 soft heads I got from MCM that are fine for only recording tapes. When I aligned these heads there would be one strong track and on weak one if the azimuth was off. My point is that it will take a while to understand why the azimuth affects each track differently (I hope I haven't totally confused you). It usually hits me a few days later. If I had your e-mail address I would tell you what happens, but it is understandable that some people don't like to pass it around. Therefore I will post a message on this NG when I know something. Also, concerning your comments about setting EQ etc. I have noticed that the Dolby is way off when using a tape from another deck. I have started recording with Dolby off and get much better results. The adjustment pots on this Fisher are labeled on the board. I don't know what to do with them though. Possibly after I get these heads aligned you will help me with the electronics. Thanks a lot BG, even if this deck turns out to be a scrapper I have learned a lot. Sincerely, Mark "bg" wrote in message ... It sounds as though you have enough guides to make it work. Alignment tapes are usually full track. You can't set tracking with it but you can use it for azimuth. Hopefully the fixed guides are in the right position. My gut feel is that the azimuth would be the only adjustment you need to make unless the guides were moved somehow. The normal method for setting the head height is to record a tone on the tape and then measure the track positions with a toolmakers microscope. I'm sure you don't have this equipment, so the next best thing would be to record a 1000 hz tone on a known good cassette deck and use that tape as your tracking standard. As you play the tape back in the Fisher deck, lightly push or lift the playback head to see if the playback level increases. If the guide on your playback head hasn't been moved, your tracking should be OK. Flip the tape over and check the levels again. For every .001 inch that the tracking is off, you lose about .4db of signal level. If the levels are within 1/2 to 1 db from side one, you probably won't be able to improve the tracking by moving the playback head guide. Moving it that small amount would be very difficult, and the guides have to be wider than the tape by about .001 inch to allow the tape to fit thru it anyway. So .001 of tape movement is perfectly normal. To set azimuth on the playback head, use the 10 khz tone on your alignment tape. There's two ways to do this. One way is to simply adjust your playback head azimuth for maximum output at 10 khz. The other method is to measure the phase between the left and right tracks. (lissajous patterns) Set up your scope for X-Y mode. Plug the left line out into one channel and the right line out into the other channel. When the two tracks are in perfect phase alignment, the scope trace should make a line angled at 45 degrees . It looks like this -- (/) . If the phase alignment is out by 180 degrees the line is angled like this ---- (\). Between 0 and 180 degrees the line changes to an oval or a circle. Multiples of 360 degrees will look like it's in phase alignment, but the length of the line will get shorter. So what you want is the longest line possible angled like (/). Note that when the azimuth is off, the level of the 10 khz tone drops off. Lower frequencies are barely affected by bad azimuth, that's why it is set using a higher frequency tone. If the 45 degree line fluctuates rapidly, there is a problem with the tape moving up and down. This might be due to the guides not all being at the same height or bad zenith. Your alignment tape might be stretched also. It doesn't take very much abuse to stretch a tape. If the tape seems to be bad , try recording a 10k tone on a good cassette deck and use that for your alignment tape. Now that the playback head is in correct azimuth and height. You can align your record head to your playback head. Check the height of the record head by recording a 1000 hz tone. Move the record head up or down until you get maximum output from the playback head. Again, if you flip the tape over, the levels should playback within about 1db. seeing as the record head has a guide welded to it , there should be no reason for the record head tracking to be incorrect. Set the azimuth by recording a 10khz tone and adjust the record head azimuth for maximum output from the playback head or 0 degree phase shift between left and right outputs. You might need to set levels, EQ, bias, and calibrate the VU meters. This would be hard to do unless the adjustment pots are marked on the circuit board, but not impossible to figure out. Let me know how you make out. Marko wrote in message ... BG: OK let's give it a try. This time I will get it right about where the guides are Originally this machine had four guides: (1) one solidly affixed to left of erase head (2) one on left of record head, but affixed to the transport frame (3) One spot welded to the right side of the record head (4) One affixed (with miniature screw) to left side of PB head The one on the right side of the record head is less than a cm from the guide on the left of the PB head (PB head guide is effectively missing, not repairable, mangled) As far as stability of the tape going across the heads goes, I feel that the 3 remaining guides will be enough, if they are aligned The two problems are as follows: (1) The guide to the left of the record head is affixed to frame and all other guides must correspond to this one or the tape will not ride smoothly on the heads. (2) Seems like the guide to the right of the record head should not effect the path of the tape over the PB head because it is over the screw that is not for adjustment (the mounting screw that is tightened and not adjustable). BUT, it does because I didn't notice the 3rd head when I was adjusting the azimuth for the record head (I thought it was the playback head at the time). Turning the azimuth adjustment for the record head affects the path of the tape over the PB head. I recall seeing the PB amplitude vary on a scope as the azimuth screw for Rec head was turned. I hope I have written this in a readable manner. All I can see is that I should adjust the Rec and PB heads over and over until hopefully they are aligned. Any ideas or warnings, BG? Thanks for your help. Your advice has given me a much needed understanding of this situation. Mark "bg" wrote in message ... Just about every deck I've ever seen has a guide on the ingoing side of the erase head and a guide on the outgoing side of the playback head, with no other guides in between. It is also common practise to affix the guides to the heads, not the chassis. On the chassis there will be posts that hold the shell in place, they are not tape guides. I have plenty of time . If you are ready to continue let me know bg Marko wrote in message ... BG: I have reread your post several times and now realize that without the guide on the PB head then it is up to me and luck to get it going right. Unless you have some more advice, thanks much, you've been a great help. Sincerely, Mark "bg" wrote in message ... The heads from left to right are, the erase head, the record head and the playback head. Any cassette I've ever seen has a guide attached to the playback head. If possible, bend the damaged guide back into place. Usually this guide is spot welded, therefore the height of the guide might not have changed. This guide sets the tracking which usually is not adjustable because the guide is fixed to the playback head at the factory. On rare occasions this guide is adjustable. The tilt of the head sets azimuth which is adjustable on all decks. You will have to examine the record and playback heads to see if there is azimuth adjustments for both heads. I would expect there is. Head height raises or lowers the position of the head gaps on the tape. Azimuth rotates the gaps so that they are aligned perpendicular (90 degrees) to the tape. Azimuth will have a slight effect on the head height. Another head adjustment you might have is zenith. Usually located at the rear of the head, it tilts the face of the head, so that the head is parallel to the tape. This adjustment if incorrect, would tilt the top of the head either closer or further from the tape than the bottom of the head. It causes uneven head wear and it causes the tape to scew up and down. As the tape scews, the azimuth and tracking will also be out of adjustment. The erase head should also have a non adjustable guide affixed to it. Check to see that you have these guides in place, the azimuth and zenith adjustments, and that the adjustments will move the heads. If you can't physically align the heads, or the guides are bad, there is no sense in going any further. you will have to replace whatever mechanics are bad. You might want to sacrafice an old cassette by cutting away the plastic shell in the area where the heads contact the tape. This will give you the abiltiy to see how the tape rides over the heads. If the tape is visibly moving up or down, you will have to correct this. It is impossible to align a head to tape that moves all over the place. The basic concept is to set all guides at the same height so that the tape enters the shell and leaves the shell at the same height. Any guides in between should not raise or lower the tape as it travels thru the shell. Post back here with your results and we'll determine the next step. bg Marko wrote in message ... BG: I thought I would check for replies just one more time before I stopped NG activity for awhile. Glad I did. I have a signal generator, alignment tape, scope, and HP5210 freq meter that I have used to set the motor RPM with 1KHz test tone. I haven't checked yet, but I am hoping that (1) the head on the far right is the play head (2) the tape monitor switch will allow me to record a test tone (I will use 10KHz) and then monitor it with the play head so that I can align the record head. (3) that the tape guide on the PB head (which has been bent out of the tape path) is not necessary for proper tape transfer over the heads. What worries me is that the tape guide is on the record head and I must align the playback head first. I didn't notice the third head at first and aligned the playback with the record head adjustment screw. This worked because the tape guide is on the record head. How do I start out with proper alignment of the two tape guides before aligning the heads? One guide, the first one, is affixed to the transport frame and the second guide is affixed to the record head. I think this problem may have been encountered by whoever worked on it before it was sent to a resale shop. I could see that they had disturbed the paint on the screws. It also had two stretched belts and a very dirty rec/play switch on the board, so I'm not sure. The belts may have stretched and the grease in the switch may have dried from sitting on the shelf for years after they encountered the alignment problem. What do you suggest? Sincerely, Mark (this is a top post) ----- Original Message ----- From: "bg" Newsgroups: sci.electronics.repair Sent: Sunday, July 27, 2003 11:46 PM Subject: Fisher cassette heads You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark "bg" wrote in message ... You need an audio generator, and an AC audio voltmeter with a DB scale. If you have this equipment I'll steer you through it. bg Marko wrote in message ... I have a Fisher cassette deck with separate record and playback heads. I assume that the one in the middle, the large one, is the record head. I have a professional alignment tape. How does one align the record head? There is a tape monitor switch which probably is used to compare input to output. These are ferrite heads with no visible wear, new belts, switches cleaned thoroughly: this deck is worth an alignment as opposed to the trash can (mabey). Also, one tape guide (the one on the far left, just to the left of the record head) is affixed to the transport frame. The second guide is affixed to the record head. The third tape guide on the playback head is bent over to the side, obviously bent intentionally to get it out of the way. The adjustment screw to this bent guide is not accessable for adjustment (sloppy design). The third tape guide is probably not necessary since it is only about a cm from the guide on the record head. This transport may be a piece of junk due to lousy design. Any helpful hints will be appreciated Thanks, Mark |
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