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Repairing vintage Philips 7871 receiver
sickrick wrote in message
... Hey all, I have a small (but major) problem with my Philips 7871 receiver. The treble pot only controls the right channel. The left channel is stuck on 0 dB: when i turn the pot, there is no change in the sound. The pot works fine with the right channel and the bass pot works fine with both channels. I have a feeling I need to buy a multimeter, but its been many years since I used one and I've completely forgotten how to use it. I also am looking for a service/repair manual for this, but I can't find one. I took off the casing and looked around for any visual clues, but everything looks fine inside. A few questions: Is there anything else I should look for? Anyone here have experience repairing this particular piece of equipment? If I bought a multimeter, how would I go about troubleshooting this problem? How much would it cost to repair this problem if I took it to a tech Any idea where I could find a service/repair manual? Please help!!! Thanks Rick A crystal earpiece is about the only piece of test equipment you need for this sort or repair, in all probability. To check the central pins of the treble control pot to start with. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
Repairing vintage Philips 7871 receiver
"N_Cook" wrote in message ... sickrick wrote in message ... Hey all, I have a small (but major) problem with my Philips 7871 receiver. The treble pot only controls the right channel. The left channel is stuck on 0 dB: when i turn the pot, there is no change in the sound. The pot works fine with the right channel and the bass pot works fine with both channels. I have a feeling I need to buy a multimeter, but its been many years since I used one and I've completely forgotten how to use it. I also am looking for a service/repair manual for this, but I can't find one. I took off the casing and looked around for any visual clues, but everything looks fine inside. A few questions: Is there anything else I should look for? Anyone here have experience repairing this particular piece of equipment? If I bought a multimeter, how would I go about troubleshooting this problem? How much would it cost to repair this problem if I took it to a tech Any idea where I could find a service/repair manual? Please help!!! Thanks Rick Is there a tone control defeat switch (sometimes called flat) on this unit? If so push it on and off a few times and see if the tone function is restored. You should also try turning the affected control back and forth several times. David |
Repairing vintage Philips 7871 receiver
Hey all,
I have a small (but major) problem with my Philips 7871 receiver. The treble pot only controls the right channel. The left channel is stuck on 0 dB: when i turn the pot, there is no change in the sound. The pot works fine with the right channel and the bass pot works fine with both channels. I have a feeling I need to buy a multimeter, but its been many years since I used one and I've completely forgotten how to use it. I also am looking for a service/repair manual for this, but I can't find one. I took off the casing and looked around for any visual clues, but everything looks fine inside. A few questions: Is there anything else I should look for? Anyone here have experience repairing this particular piece of equipment? If I bought a multimeter, how would I go about troubleshooting this problem? How much would it cost to repair this problem if I took it to a tech Any idea where I could find a service/repair manual? Please help!!! Thanks Rick |
Repairing vintage Philips 7871 receiver
"sickrick" wrote in message ... In article , "David" wrote: Is there a tone control defeat switch (sometimes called flat) on this unit? If so push it on and off a few times and see if the tone function is restored. You should also try turning the affected control back and forth several times. David Is this switch usually on the inside of the device? I'm looking for it, but I can't find anything like that...its just a tone control bypass switch? I don't think this unit has one... I tried dialing the treble pot back and forth, but it does nothing...this problem is consistent and there is no scratchy sound or cutting in and out thanks If this unit has such a switch, it would be on the front panel. It looks like you need at least an ohmmeter to see if the pot if working correctly. If it is working properly by comparing readings from both channels, then post back. David |
Repairing vintage Philips 7871 receiver
In article ,
sickrick wrote: Ugh I hope I don't have to replace the treble control pot, that would be a pain with the way its layed out... Unfortunately, I suspect that you may very well need to. The symptoms lead me to suspect that the pot has gone open... either the wiper has broken, or the conductive track has been worn through. Since pots are mechanical contrivances, they're subject to mechanical wear-out. I'd guess that the three most common age-related problems in vintage receivers of this sort are open/noisy switches, open/noisy pots, and bad (leaky or high-ESR) electrolytic capacitors. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Repairing vintage Philips 7871 receiver
In article ,
"N_Cook" wrote: A crystal earpiece is about the only piece of test equipment you need for this sort or repair, in all probability. To check the central pins of the treble control pot to start with. Ok, I'll pick one up...but I have never used one before, can you point me to some info on how to use one? I am assuming that i would not use the jack plug, but would instead cut it off and ground the wire while probing the treble control pins with the other wire? Ugh I hope I don't have to replace the treble control pot, that would be a pain with the way its layed out... |
Repairing vintage Philips 7871 receiver
In article ,
"David" wrote: Is there a tone control defeat switch (sometimes called flat) on this unit? If so push it on and off a few times and see if the tone function is restored. You should also try turning the affected control back and forth several times. David Is this switch usually on the inside of the device? I'm looking for it, but I can't find anything like that...its just a tone control bypass switch? I don't think this unit has one... I tried dialing the treble pot back and forth, but it does nothing...this problem is consistent and there is no scratchy sound or cutting in and out thanks |
Repairing vintage Philips 7871 receiver
On Apr 3, 3:25*pm, sickrick wrote:
Hey all, I have a small (but major) problem with my Philips 7871 receiver. *The treble pot only controls the right channel. *The left channel is stuck on 0 dB: when i turn the pot, there is no change in the sound. *The pot works fine with the right channel and the bass pot works fine with both channels. *I have a feeling I need to buy a multimeter, but its been many years since I used one and I've completely forgotten how to use it. * I also am looking for a service/repair manual for this, but I can't find one. *I took off the casing and looked around for any visual clues, but everything looks fine inside. *A few questions: Is there anything else I should look for? * Anyone here have experience repairing this particular piece of equipment? * If I bought a multimeter, how would I go about troubleshooting this problem? How much would it cost to repair this problem if I took it to a tech Any idea where I could find a service/repair manual? Please help!!! Thanks Rick Sounds like the wiper has lost contact with the slip ring inside due to either oxidation or dried up grease. Just get ahold of some Caig Deoxit spray. Shoot it into the opening where the solder lugs/pc pins enter cover. It may be difficult to get to depending on the orientation of the pot in relation to everything around it. I've made extensions for the spray tube out of creativly manipulated shrink tubing.....saves alot of tear down when it works. |
Repairing vintage Philips 7871 receiver
On 4/3/2009 12:58 PM sickrick spake thus:
In article , "N_Cook" wrote: A crystal earpiece is about the only piece of test equipment you need for this sort or repair, in all probability. To check the central pins of the treble control pot to start with. Ok, I'll pick one up...but I have never used one before, can you point me to some info on how to use one? I am assuming that i would not use the jack plug, but would instead cut it off and ground the wire while probing the treble control pins with the other wire? Ugh I hope I don't have to replace the treble control pot, that would be a pain with the way its layed out... Forget the "crystal earpiece". It's an obsolete piece of hardware you'll find very difficult to find, and not what's needed here anyhow. You'll have to excuse "N_Cook", who is an inveterate bodger and tinker. You need a multimeter (aka VOM); any kind will do, digital or analog. (The digital ones sell for as little as $3 in the US.) Put it on one of the resistance measuring scales and measure the resistance between the wiper (center terminal) and one of the outer terminals as you turn the control; the resistance should change smoothly between (X ohms) and 0 ohms. If it doesn't, the control is shot and needs to be replaced. Surprised nobody has suggested the first thing to do, which is to squirt some electronic cleaner into the pot and try to clean it. Often this is all that's needed to fix a scratchy or non-working control. Be sure to use something made for cleaning electronic components, not something like WD-40. -- Made From Pears: Pretty good chance that the product is at least mostly pears. Made With Pears: Pretty good chance that pears will be detectable in the product. Contains Pears: One pear seed per multiple tons of product. (with apologies to Dorothy L. Sayers) |
Repairing vintage Philips 7871 receiver
sickrick wrote: Hey all, I have a small (but major) problem with my Philips 7871 receiver. The treble pot only controls the right channel. The left channel is stuck on 0 dB: when i turn the pot, there is no change in the sound. The pot works fine with the right channel and the bass pot works fine with both channels. I have a feeling I need to buy a multimeter, but its been many years since I used one and I've completely forgotten how to use it. I also am looking for a service/repair manual for this, but I can't find one. I took off the casing and looked around for any visual clues, but everything looks fine inside. A few questions: Is there anything else I should look for? Anyone here have experience repairing this particular piece of equipment? If I bought a multimeter, how would I go about troubleshooting this problem? How much would it cost to repair this problem if I took it to a tech Any idea where I could find a service/repair manual? Please help!!! news:rec.antiques.radio+phono -- And another motherboard bites the dust! |
Repairing vintage Philips 7871 receiver
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Repairing vintage Philips 7871 receiver
In article m,
David Nebenzahl wrote: On 4/3/2009 12:58 PM sickrick spake thus: In article , "N_Cook" wrote: A crystal earpiece is about the only piece of test equipment you need for this sort or repair, in all probability. To check the central pins of the treble control pot to start with. Ok, I'll pick one up...but I have never used one before, can you point me to some info on how to use one? I am assuming that i would not use the jack plug, but would instead cut it off and ground the wire while probing the treble control pins with the other wire? Ugh I hope I don't have to replace the treble control pot, that would be a pain with the way its layed out... Forget the "crystal earpiece". It's an obsolete piece of hardware you'll find very difficult to find, and not what's needed here anyhow. You'll have to excuse "N_Cook", who is an inveterate bodger and tinker. You need a multimeter (aka VOM); any kind will do, digital or analog. (The digital ones sell for as little as $3 in the US.) Put it on one of the resistance measuring scales and measure the resistance between the wiper (center terminal) and one of the outer terminals as you turn the control; the resistance should change smoothly between (X ohms) and 0 ohms. If it doesn't, the control is shot and needs to be replaced. Surprised nobody has suggested the first thing to do, which is to squirt some electronic cleaner into the pot and try to clean it. Often this is all that's needed to fix a scratchy or non-working control. Be sure to use something made for cleaning electronic components, not something like WD-40. i think the pot itself is fine: the same pot controls the right channel which sounds fine...are you guys saying the pot itself is stereo? there are 6 pins on the pot |
Repairing vintage Philips 7871 receiver
On 4/3/2009 3:45 PM sickrick spake thus:
i think the pot itself is fine: the same pot controls the right channel which sounds fine...are you guys saying the pot itself is stereo? there are 6 pins on the pot "The pot" is actually 2 pots ganged together mechanically, one for each channel. Each pot has 3 connections; the outer connections to the resistance, and the center "wiper" that gives you the variable resistance. It's possible that one of the 2 pots is bad. -- Made From Pears: Pretty good chance that the product is at least mostly pears. Made With Pears: Pretty good chance that pears will be detectable in the product. Contains Pears: One pear seed per multiple tons of product. (with apologies to Dorothy L. Sayers) |
Repairing vintage Philips 7871 receiver
On Apr 3, 7:27*pm, David Nebenzahl wrote:
On 4/3/2009 3:45 PM sickrick spake thus: i think the pot itself is fine: the same pot controls the right channel which sounds fine...are you guys saying the pot itself is stereo? *there are 6 pins on the pot "The pot" is actually 2 pots ganged together mechanically, one for each channel. Each pot has 3 connections; the outer connections to the resistance, and the center "wiper" that gives you the variable resistance. It's possible that one of the 2 pots is bad. -- Made From Pears: Pretty good chance that the product is at least mostly pears. Made With Pears: Pretty good chance that pears will be detectable in the product. Contains Pears: *One pear seed per multiple tons of product. (with apologies to Dorothy L. Sayers) I agree with David, spray some tuner cleaner, or even Old Spice aftershave or WD-40 into the two sections of the pot and see what happens, you don't have anything to lose, and it has fixed many an old pot for me over the last 40+ years. Bob Hofmann |
Repairing vintage Philips 7871 receiver
On Fri, 03 Apr 2009 14:25:28 -0500, sickrick wrote:
:Hey all, : :I have a small (but major) problem with my Philips 7871 receiver. The :treble pot only controls the right channel. The left channel is stuck :on 0 dB: when i turn the pot, there is no change in the sound. The pot :works fine with the right channel and the bass pot works fine with both :channels. I have a feeling I need to buy a multimeter, but its been :many years since I used one and I've completely forgotten how to use it. :I also am looking for a service/repair manual for this, but I can't find :one. I took off the casing and looked around for any visual clues, but :everything looks fine inside. A few questions: : :Is there anything else I should look for? : :Anyone here have experience repairing this particular piece of :equipment? : :If I bought a multimeter, how would I go about troubleshooting this :problem? : :How much would it cost to repair this problem if I took it to a tech : :Any idea where I could find a service/repair manual? : :Please help!!! : :Thanks :Rick If you subscribe to this forum http://www.audiokarma.org/forums/showthread.php?t=51608 you might be able to contact Brian. He seems to have a manual. |
Repairing vintage Philips 7871 receiver
"sickrick" wrote in message
... In article m, David Nebenzahl wrote: On 4/3/2009 12:58 PM sickrick spake thus: In article , "N_Cook" wrote: A crystal earpiece is about the only piece of test equipment you need for this sort or repair, in all probability. To check the central pins of the treble control pot to start with. Ok, I'll pick one up...but I have never used one before, can you point me to some info on how to use one? I am assuming that i would not use the jack plug, but would instead cut it off and ground the wire while probing the treble control pins with the other wire? Ugh I hope I don't have to replace the treble control pot, that would be a pain with the way its layed out... Forget the "crystal earpiece". It's an obsolete piece of hardware you'll find very difficult to find, and not what's needed here anyhow. You'll have to excuse "N_Cook", who is an inveterate bodger and tinker. You need a multimeter (aka VOM); any kind will do, digital or analog. (The digital ones sell for as little as $3 in the US.) Put it on one of the resistance measuring scales and measure the resistance between the wiper (center terminal) and one of the outer terminals as you turn the control; the resistance should change smoothly between (X ohms) and 0 ohms. If it doesn't, the control is shot and needs to be replaced. Surprised nobody has suggested the first thing to do, which is to squirt some electronic cleaner into the pot and try to clean it. Often this is all that's needed to fix a scratchy or non-working control. Be sure to use something made for cleaning electronic components, not something like WD-40. i think the pot itself is fine: the same pot controls the right channel which sounds fine...are you guys saying the pot itself is stereo? there are 6 pins on the pot Let's not ignore the possibility of a simple bad solder connection at the control itself... Mark Z. |
Repairing vintage Philips 7871 receiver
I agree with David, spray some tuner cleaner, or even Old Spice
aftershave or WD-40 into the two sections of the pot and see what happens, you don't have anything to lose, and it has fixed many an old pot for me over the last 40+ years. Bob Hofmann Yuck! why not just swish it around in gasoline, spit in the back and give it big WHUMP! Seriously, tuner wash was good stuff but tuners don't have switches anymore so it's gone! Isopropyl 90% is a cheap and safe wash (70% has too much water) followed by a drop of very light mineral oil (baby oil). I suspect there is a lot of Isopropyl in Old Spice. WD-40 leaves a crusty residue as a corrosion inhibitor. Around here a spray can of Isopropyl costs $15 a can at the electronic emporium vs. $2 a bottle at the drug store. I can make the can last 5-10 years. |
Repairing vintage Philips 7871 receiver
sickrick wrote:
I tried dialing the treble pot back and forth, but it does nothing...this problem is consistent and there is no scratchy sound or cutting in and out Probably a simple dry joint on one of the center pins of the treble pot. Should be very easy to fix by cleaning & resoldering. -- W . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^--------------------------------------------------------------- |
Repairing vintage Philips 7871 receiver
sickrick wrote:
Hey all, I have a small (but major) problem with my Philips 7871 receiver. The treble pot only controls the right channel. The left channel is stuck on 0 dB: when i turn the pot, there is no change in the sound. The pot works fine with the right channel and the bass pot works fine with both channels. I have a feeling I need to buy a multimeter, but its been many years since I used one and I've completely forgotten how to use it. I also am looking for a service/repair manual for this, but I can't find one. I took off the casing and looked around for any visual clues, but everything looks fine inside. A few questions: Is there anything else I should look for? Anyone here have experience repairing this particular piece of equipment? If I bought a multimeter, how would I go about troubleshooting this problem? How much would it cost to repair this problem if I took it to a tech Any idea where I could find a service/repair manual? Please help!!! Thanks Rick I found the schematic for this set. There is a high cut filter switch which if failing, could be affecting the high end. Also, there is a small 1uF capacitor, C233, that may be affecting the frequency response. It should be fairly simple for an experienced technician to compare the left channel to the right and figure out where the problem is. Good luck. -- David Farber David Farber's Service Center L.A., CA |
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