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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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#1
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Update on the Fender ...
So, the nonsense bias board arrived. It was in a properly printed Fender
cardboard-topped 'accessory' bag, as you might find hanging on pegboard in any music shop. "Genuine Fender Parts" it proudly announces. "PCB ASSY AUTOMATIC BIAS 4 TUBES S - S" I'm not sure what that tells us exactly, but if Fender have them all bagged up ready to hang up in dealers ... ?? Anyways, put it in and fired it up. It does a lot of LED flashing and bias trimming between the 4 tubes, but seems to eventually settle on a 'solution'. Out of the four (brand-new looking) Sovtek output tubes, three ended up with almost -ve 51 volts on their grids, and the other with just under -ve 52 volts. For all of this effort though, I'm not sure that there would have been any practical difference if all four tubes were to have had the same bias on them. I don't know if these Sovteks were bought as a matched quad - we didn't fit them - but clearly they aren't, quite. I don't know how much 'slack' this board is able to take up, but I would imagine quite a bit. But the thing that's vexing me a bit now, is whether to recommend that the owner replaces all four tubes now for a properly matched quad. There's no signs of any flashovers or other nasties going on, but I still have that niggling doubt that something might have ****ted that board, and that one of the outputs clearly doesn't quite match the other three. Thing is, it's already going to have cost them a bit in bench time, even if we let the board go in for no cost, and to then add a set of output valves that it looks like have already been replaced not long ago ... :-\ Arfa |
#2
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Update on the Fender ...
Anyways, put it in and fired it up. It does a lot of LED flashing and bias trimming between the 4 tubes, but seems to eventually settle on a 'solution'. Out of the four (brand-new looking) Sovtek output tubes, three ended up with almost -ve 51 volts on their grids, and the other with just under -ve 52 volts. For all of this effort though, I'm not sure that there would have been any practical difference if all four tubes were to have had the same bias on them. I don't know if these Sovteks were bought as a matched quad - we didn't fit them - but clearly they aren't, quite. I don't know how much 'slack' this board is able to take up, but I would imagine quite a bit. But the thing that's vexing me a bit now, is whether to recommend that the owner replaces all four tubes now for a properly matched quad. There's no signs of any flashovers or other nasties going on, but I still have that niggling doubt that something might have ****ted that board, and that one of the outputs clearly doesn't quite match the other three. Thing is, it's already going to have cost them a bit in bench time, even if we let the board go in for no cost, and to then add a set of output valves that it looks like have already been replaced not long ago ... :-\ Arfa Why would you need a properly matched quad in an amp that measures each tube's bias point and matches it to the rest? Surely that's just like having 4 separate bias pots onboard, something very few amps have. If one tube is down, swap its position and see if the amp compensates accordingly. So either tube or amp problem. Plus the bias current is actually measured and set per tube in the amp, at the voltages that the tubes are actually running at. Not some arbitrary set of parameters remotely measured in a tube tester that the tube supplier claims to have carried out to "match" them. Gareth. |
#3
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Update on the Fender ...
"Gareth Magennis" wrote in message ... Anyways, put it in and fired it up. It does a lot of LED flashing and bias trimming between the 4 tubes, but seems to eventually settle on a 'solution'. Out of the four (brand-new looking) Sovtek output tubes, three ended up with almost -ve 51 volts on their grids, and the other with just under -ve 52 volts. For all of this effort though, I'm not sure that there would have been any practical difference if all four tubes were to have had the same bias on them. I don't know if these Sovteks were bought as a matched quad - we didn't fit them - but clearly they aren't, quite. I don't know how much 'slack' this board is able to take up, but I would imagine quite a bit. But the thing that's vexing me a bit now, is whether to recommend that the owner replaces all four tubes now for a properly matched quad. There's no signs of any flashovers or other nasties going on, but I still have that niggling doubt that something might have ****ted that board, and that one of the outputs clearly doesn't quite match the other three. Thing is, it's already going to have cost them a bit in bench time, even if we let the board go in for no cost, and to then add a set of output valves that it looks like have already been replaced not long ago ... :-\ Arfa Why would you need a properly matched quad in an amp that measures each tube's bias point and matches it to the rest? Surely that's just like having 4 separate bias pots onboard, something very few amps have. If one tube is down, swap its position and see if the amp compensates accordingly. So either tube or amp problem. Plus the bias current is actually measured and set per tube in the amp, at the voltages that the tubes are actually running at. Not some arbitrary set of parameters remotely measured in a tube tester that the tube supplier claims to have carried out to "match" them. Gareth. I hear what you are saying Gareth, and I take your point, but you are missing the point that I am making. What is concerning me is that the original board has failed. I cannot know whether this is a 'chance' failure, or whether it's been knocked out by - for instance - an intermittent internal short on one of the valves, bearing in mind that it is connected directly to all four grids and all four cathodes. The fact that one of the valves clearly has rather different characteristics from the other three, just rang slight alarm bells in this regard, particularly as the valves all look almost new, so were *probably* fitted as a matched quad, although again, I cannot actually know this, as we didn't fit them. You of course make a valid point that the whole purpose of this automatic bias / balance board is so that it can match anything from 2 x 6L6 + 2 x EL34, to a set of four 19 set PA valves, and it is of course doing its job here in correcting for the odd man out - if that is in fact *all* that it is .... Arfa |
#4
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Update on the Fender ...
In article ,
Arfa Daily wrote: I hear what you are saying Gareth, and I take your point, but you are missing the point that I am making. What is concerning me is that the original board has failed. I cannot know whether this is a 'chance' failure, or whether it's been knocked out by - for instance - an intermittent internal short on one of the valves, bearing in mind that it is connected directly to all four grids and all four cathodes. The fact that one of the valves clearly has rather different characteristics from the other three, just rang slight alarm bells in this regard, particularly as the valves all look almost new, so were *probably* fitted as a matched quad, although again, I cannot actually know this, as we didn't fit them. You of course make a valid point that the whole purpose of this automatic bias / balance board is so that it can match anything from 2 x 6L6 + 2 x EL34, to a set of four 19 set PA valves, and it is of course doing its job here in correcting for the odd man out - if that is in fact *all* that it is ... As far as checking the Fender itself for hidden damage - I think the "swap the tubes around and track the bias changes" idea is a good one. With three rotations, you could test each tube in each socket position. See if the bias for each individual tube "follows" the tube pretty exactly, or if one or more sockets have a (forgive me) biased bias. This would give you some idea as to whether anything in one of the board sections was "cooked" by a tube failure (maybe a resistor overheated and has drifted?) As to the tubes themselves... best you can do is report your findings to the owner, make your best recommendation, and ask whether the owner wants you to install a fresh set that you've personally matched. What does a good transconductance tester tell you about the tubes? |
#5
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Update on the Fender ...
On 17/11/2014 11:16, Arfa Daily wrote:
So, the nonsense bias board arrived. It was in a properly printed Fender cardboard-topped 'accessory' bag, as you might find hanging on pegboard in any music shop. "Genuine Fender Parts" it proudly announces. "PCB ASSY AUTOMATIC BIAS 4 TUBES S - S" I'm not sure what that tells us exactly, but if Fender have them all bagged up ready to hang up in dealers ... ?? Anyways, put it in and fired it up. It does a lot of LED flashing and bias trimming between the 4 tubes, but seems to eventually settle on a 'solution'. Out of the four (brand-new looking) Sovtek output tubes, three ended up with almost -ve 51 volts on their grids, and the other with just under -ve 52 volts. For all of this effort though, I'm not sure that there would have been any practical difference if all four tubes were to have had the same bias on them. I don't know if these Sovteks were bought as a matched quad - we didn't fit them - but clearly they aren't, quite. I don't know how much 'slack' this board is able to take up, but I would imagine quite a bit. But the thing that's vexing me a bit now, is whether to recommend that the owner replaces all four tubes now for a properly matched quad. There's no signs of any flashovers or other nasties going on, but I still have that niggling doubt that something might have ****ted that board, and that one of the outputs clearly doesn't quite match the other three. Thing is, it's already going to have cost them a bit in bench time, even if we let the board go in for no cost, and to then add a set of output valves that it looks like have already been replaced not long ago ... :-\ Arfa Useless bloody thunderbird, I remember reading the original of this story but cannot now find it or could you at least repeat the model number. What was the failure in the board, could you tell whether over-current or over-voltage, any deliberate track thinnings for tell-tales. |
#6
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Update on the Fender ...
"Arfa Daily" wrote in message ... "Gareth Magennis" wrote in message ... Anyways, put it in and fired it up. It does a lot of LED flashing and bias trimming between the 4 tubes, but seems to eventually settle on a 'solution'. Out of the four (brand-new looking) Sovtek output tubes, three ended up with almost -ve 51 volts on their grids, and the other with just under -ve 52 volts. For all of this effort though, I'm not sure that there would have been any practical difference if all four tubes were to have had the same bias on them. I don't know if these Sovteks were bought as a matched quad - we didn't fit them - but clearly they aren't, quite. I don't know how much 'slack' this board is able to take up, but I would imagine quite a bit. But the thing that's vexing me a bit now, is whether to recommend that the owner replaces all four tubes now for a properly matched quad. There's no signs of any flashovers or other nasties going on, but I still have that niggling doubt that something might have ****ted that board, and that one of the outputs clearly doesn't quite match the other three. Thing is, it's already going to have cost them a bit in bench time, even if we let the board go in for no cost, and to then add a set of output valves that it looks like have already been replaced not long ago ... :-\ Arfa Why would you need a properly matched quad in an amp that measures each tube's bias point and matches it to the rest? Surely that's just like having 4 separate bias pots onboard, something very few amps have. If one tube is down, swap its position and see if the amp compensates accordingly. So either tube or amp problem. Plus the bias current is actually measured and set per tube in the amp, at the voltages that the tubes are actually running at. Not some arbitrary set of parameters remotely measured in a tube tester that the tube supplier claims to have carried out to "match" them. Gareth. I hear what you are saying Gareth, and I take your point, but you are missing the point that I am making. What is concerning me is that the original board has failed. I cannot know whether this is a 'chance' failure, or whether it's been knocked out by - for instance - an intermittent internal short on one of the valves, bearing in mind that it is connected directly to all four grids and all four cathodes. The fact that one of the valves clearly has rather different characteristics from the other three, just rang slight alarm bells in this regard, particularly as the valves all look almost new, so were *probably* fitted as a matched quad, although again, I cannot actually know this, as we didn't fit them. You of course make a valid point that the whole purpose of this automatic bias / balance board is so that it can match anything from 2 x 6L6 + 2 x EL34, to a set of four 19 set PA valves, and it is of course doing its job here in correcting for the odd man out - if that is in fact *all* that it is ... Arfa Ah, sorry I did miss the point. I would tend to assume that these were not a matched quad, as people who match and sell valves generally like to make this known by marking the valves with either a sticker or sharpie on the glass. Although its more difficult with EL84's because they don't have a nice base for the sticker and the glass is small to mark well in this manner. I buy my valves 50 at a time direct from JJ Tesla in Slovakia. I've built a tester with variable regulated HT and constant current sources to match the valves at a known voltage and current point. A quick check of the EL84 box shows about a 10% variation between lowest and highest. It looks like the readings are probably within a Gaussian distribution, or whatever the correct Statistical term is involved here, i.e. the majority are clumped in the middle with increasingly fewer being lower or higher than the mid point. Your readings seem to indicate around a 2% difference between the "bad one" and the others. I'd say this might be pretty typical of a non matched set? But who really knows, as you are saying! Cheers, Gareth. |
#7
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Update on the Fender ...
Arfa Daily wrote:
So, the nonsense bias board arrived. ** The "nonsense" is all coming from you - ****head. Anyways, put it in and fired it up It does a lot of LED flashing and bias trimming between the 4 tubes, but seems to eventually settle on a 'solution'. Out of the four (brand-new looking) Sovtek output tubes, three ended up with almost -ve 51 volts on their grids, and the other with just under -ve 52 volts. For all of this effort though, I'm not sure that there would have been any practical difference if all four tubes were to have had the same bias on them. I don't know if these Sovteks were bought as a matched quad - we didn't fit them - but clearly they aren't, quite. ** One valve, 1 volt out is about as near to matched as any 4 output valves I have ever seen or ever need to be. Jesus Christ you are a neurotic ****. I don't know how much 'slack' this board is able to take up, but I would imagine quite a bit. ** The 4 bias currents are IDENTICAL !! You stupid ****. owner replaces all four tubes now for a properly matched quad. ** FFS - there is nothing improper about the set you have. There's no signs of any flashovers or other nasties going on, but I still have that niggling doubt that something might have ****ted that board, ** Fender have already told you the boards fail all on their own. and that one of the outputs clearly doesn't quite match the other three. ** Twaddle. Thing is, it's already going to have cost them a bit in bench time, even if we let the board go in for no cost, and to then add a set of output valves that it looks like have already been replaced not long ago ... :-\ ** If it ain't broke, don't fix it. Only crooks do that. .... Phil |
#8
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Update on the Fender ...
Ah, sorry I did miss the point. I would tend to assume that these were not a matched quad, as people who match and sell valves generally like to make this known by marking the valves with either a sticker or sharpie on the glass. Although its more difficult with EL84's because they don't have a nice base for the sticker and the glass is small to mark well in this manner. I buy my valves 50 at a time direct from JJ Tesla in Slovakia. I've built a tester with variable regulated HT and constant current sources to match the valves at a known voltage and current point. A quick check of the EL84 box shows about a 10% variation between lowest and highest. It looks like the readings are probably within a Gaussian distribution, or whatever the correct Statistical term is involved here, i.e. the majority are clumped in the middle with increasingly fewer being lower or higher than the mid point. Your readings seem to indicate around a 2% difference between the "bad one" and the others. I'd say this might be pretty typical of a non matched set? But who really knows, as you are saying! Cheers, Gareth. In reply to everyone, the bias did move with the valve - it was one of the first things that I checked, so the board was 'doing its thing' and balancing this valve into the other three. Information that I have since found out today, indicates that one valve was changed on its own a few months back, so I guess that's probably the one that is different, so I think I'm going to add this new knowledge to what the man at Fender said about them having had board problems, and that the new board was a pre-packaged spare, and declare it "good to go" ! Arfa |
#9
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Update on the Fender ...
"Phil Allison" wrote in message ... Arfa Daily wrote: So, the nonsense bias board arrived. ** The "nonsense" is all coming from you - ****head. The board is a nonsense piece of design. It's not needed, and only adds another layer of complexity into an item that is needed to be robust and reliable. For most purposes in this type of equipment, fixed bias at the simplest or single level-pot and sometimes a balance pot is all that is required. Owners should not be arsing about changing valves in the first place, and particularly should not be mixing types. Anyways, put it in and fired it up It does a lot of LED flashing and bias trimming between the 4 tubes, but seems to eventually settle on a 'solution'. Out of the four (brand-new looking) Sovtek output tubes, three ended up with almost -ve 51 volts on their grids, and the other with just under -ve 52 volts. For all of this effort though, I'm not sure that there would have been any practical difference if all four tubes were to have had the same bias on them. I don't know if these Sovteks were bought as a matched quad - we didn't fit them - but clearly they aren't, quite. ** One valve, 1 volt out is about as near to matched as any 4 output valves I have ever seen or ever need to be. You miss the point as always by running your stupid mouth before engaging that pathetic walnut of a brain. ****ing dope Jesus Christ you are a neurotic ****. Bwaaaahhhaaahhhaaaa !!!!! That from YOU ??!!! Neurotic ? ****head ? That would be YOU with bells on ... I don't know how much 'slack' this board is able to take up, but I would imagine quite a bit. ** The 4 bias currents are IDENTICAL !! You stupid ****. Philip. Mirror ... owner replaces all four tubes now for a properly matched quad. ** FFS - there is nothing improper about the set you have. I didn't say that there WAS. I was just examining the possibility that there MIGHT be. But then you don't actually read and understand anything before you run that dopey gob of yours, do you ? There's no signs of any flashovers or other nasties going on, but I still have that niggling doubt that something might have ****ted that board, ** Fender have already told you the boards fail all on their own. So they did. But that doesn't mean that they don't also fail as a result of something else as well. There was no serial number identification offered by Fender in regards of this bad batch. Just a statement that they had had a bad batch "around that time" when told its age. Therefore, this one may or may not have come from that batch. I can't say for sure, and YOU most certainly can't ... and that one of the outputs clearly doesn't quite match the other three. ** Twaddle. ********. If the board arrives at a solution that sets the bias near as a gnats cock identical on three of the valves, and sets the fourth a volt or so different, then that 'odd one' clearly doesn't QUITE (look the word up if you're not sure) match the other three Thing is, it's already going to have cost them a bit in bench time, even if we let the board go in for no cost, and to then add a set of output valves that it looks like have already been replaced not long ago ... :-\ ** If it ain't broke, don't fix it. Only crooks do that. And you would know, of course ... Now go take your meds, and shut the **** up. ****. Arfa ... Phil |
#10
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Update on the Fender ...
Arfa Useless bloody thunderbird, I remember reading the original of this story but cannot now find it or could you at least repeat the model number. What was the failure in the board, could you tell whether over-current or over-voltage, any deliberate track thinnings for tell-tales. It's a Supersonic 100 head. The board failed to produce any 'controlled' bias to the valves, and all four grids were at -89 volts. It looks as though it works by measuring the voltage across four low value Rs in the cathodes by using A-D inputs on the microcontroller on the board. The bias is then produced by feeding PWM signals from four port pins to driver transistors followed by filter caps. In the case of this board, the supply volts, reset pin etc were all at correct levels, but the micro did not produce any output. You could not even measure any clock at the xtal pins. No evidence of any cause was visible. Board was pristine. Double sided surface mount, and all examined under strong magnification, but no signs of any damaged components. Arfa |
#11
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Update on the Fender ...
"Arfa Daily" wrote in message ... Arfa Useless bloody thunderbird, I remember reading the original of this story but cannot now find it or could you at least repeat the model number. What was the failure in the board, could you tell whether over-current or over-voltage, any deliberate track thinnings for tell-tales. It's a Supersonic 100 head. The board failed to produce any 'controlled' bias to the valves, and all four grids were at -89 volts. It looks as though it works by measuring the voltage across four low value Rs in the cathodes by using A-D inputs on the microcontroller on the board. The bias is then produced by feeding PWM signals from four port pins to driver transistors followed by filter caps. In the case of this board, the supply volts, reset pin etc were all at correct levels, but the micro did not produce any output. You could not even measure any clock at the xtal pins. No evidence of any cause was visible. Board was pristine. Double sided surface mount, and all examined under strong magnification, but no signs of any damaged components. Arfa Any numbers on the cpu? |
#12
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Update on the Fender ...
"Tom Miller" wrote in message ... "Arfa Daily" wrote in message ... Arfa Useless bloody thunderbird, I remember reading the original of this story but cannot now find it or could you at least repeat the model number. What was the failure in the board, could you tell whether over-current or over-voltage, any deliberate track thinnings for tell-tales. It's a Supersonic 100 head. The board failed to produce any 'controlled' bias to the valves, and all four grids were at -89 volts. It looks as though it works by measuring the voltage across four low value Rs in the cathodes by using A-D inputs on the microcontroller on the board. The bias is then produced by feeding PWM signals from four port pins to driver transistors followed by filter caps. In the case of this board, the supply volts, reset pin etc were all at correct levels, but the micro did not produce any output. You could not even measure any clock at the xtal pins. No evidence of any cause was visible. Board was pristine. Double sided surface mount, and all examined under strong magnification, but no signs of any damaged components. Arfa Any numbers on the cpu? STM32F 101C6 This appears to agree with what it says on the schematic Arfa |
#13
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Update on the Fender ...
Arfa Daily wrote:
"Phil Allison" : So, the nonsense bias board arrived. ** The "nonsense" is all coming from you - ****head. The board is a nonsense piece of design. ** No it is not. ** One valve, 1 volt out is about as near to matched as any 4 output valves I have ever seen or ever need to be. You miss the point ** There was no point get - you lunatic. Jesus Christ you are a neurotic ****. ** The 4 bias currents are IDENTICAL !! You stupid ****. Philip. ** You completely missed the point, as usual. ** FFS - there is nothing improper about the set you have. I didn't say that there WAS. ** You did, three or four times. ** Fender have already told you the boards fail all on their own. So they did. ** Believe them. But that doesn't mean that they don't also fail as a result of something else as well. ** Sheer, paranoid fear of the new. If the design was that fragile, there would be constant PCB failure. You will find there is a very high resistance between the output valve grids and the bias PCB circuitry and the cathode resistors are protected from over-current too. What a dickhead. .... Phil |
#14
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Update on the Fender ...
"Arfa Daily" wrote in message news "Tom Miller" wrote in message ... "Arfa Daily" wrote in message ... Arfa Useless bloody thunderbird, I remember reading the original of this story but cannot now find it or could you at least repeat the model number. What was the failure in the board, could you tell whether over-current or over-voltage, any deliberate track thinnings for tell-tales. It's a Supersonic 100 head. The board failed to produce any 'controlled' bias to the valves, and all four grids were at -89 volts. It looks as though it works by measuring the voltage across four low value Rs in the cathodes by using A-D inputs on the microcontroller on the board. The bias is then produced by feeding PWM signals from four port pins to driver transistors followed by filter caps. In the case of this board, the supply volts, reset pin etc were all at correct levels, but the micro did not produce any output. You could not even measure any clock at the xtal pins. No evidence of any cause was visible. Board was pristine. Double sided surface mount, and all examined under strong magnification, but no signs of any damaged components. Arfa Any numbers on the cpu? STM32F 101C6 This appears to agree with what it says on the schematic Arfa Put this whole number in a search to get the datasheet. STM32F101C6 It is an ARM Cortex 32 bit CPU with 32k bytes of flash. I don't know how successful you would be copying the firmware over to a new chip.. |
#15
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Update on the Fender ...
"Phil Allison" wrote in message ... Arfa Daily wrote: "Phil Allison" : So, the nonsense bias board arrived. ** The "nonsense" is all coming from you - ****head. The board is a nonsense piece of design. ** No it is not. So, would that be more or less so than your opinion of the HK board ? And I quote from your post - "That H&K model even allows the user to change from EL34s to 6L6s. However, the system cannot cope with faulty valves and may even be damaged by them OR fail totally like you found. Also, it is sometimes possible to put an octal valve in the socket out of key or having broken the spigot install it any position you like. Results are often dramatic. IME having guitar players fool around putting valves in their amps is full of traps & hazards - owners are bound to fall into one sooner or later. " ** One valve, 1 volt out is about as near to matched as any 4 output valves I have ever seen or ever need to be. You miss the point ** There was no point get - you lunatic. Not in your wobble-eyed head ... Jesus Christ you are a neurotic ****. ** The 4 bias currents are IDENTICAL !! You stupid ****. Philip. ** You completely missed the point, as usual. ** FFS - there is nothing improper about the set you have. I didn't say that there WAS. ** You did, three or four times. Err, no, I didn't ... ** Fender have already told you the boards fail all on their own. So they did. ** Believe them. But that doesn't mean that they don't also fail as a result of something else as well. As I said ... ** Sheer, paranoid fear of the new. Oh **** off back under your stone you obnoxious arsehole. I've been in this game for 45 years. Nothing has come along in that time to make me paranoid, and this isn't going to be the first If the design was that fragile, there would be constant PCB failure. You will find there is a very high resistance between the output valve grids and the bias PCB circuitry and the cathode resistors are protected from over-current too. There is a couple of hundred k. Hardly a "very high resistance". What a dickhead. You know, you really are a sad fool, Philip. Just about any thread that anyone starts that runs for longer than a couple of days, sooner or later, there you are running your dumb - and usually foul - gob off. The trouble with you is that you have this pathetic need to try to sound superior to everyone, when in truth, you are often at least misguided, if not downright wrong. Just because something is your opinion, it doesn't necessarily make you right and everyone else wrong. Your main failing is that you do not read things properly, and then go off on one of your ill-conceived rants, based on what you *thought* you read. When your error is pointed out, you then start madly snipping in an attempt to cover up what *you* said in reply to what the poster *actually* said, and then start leveling a tirade of abuse , peppered with expletives, capital letters, exclamation marks and asterisks, at anyone who dares to challenge you. Some of the more 'delicate' posters cave in at this, but I don't know why you keep trying it with me. You've tried this crap with me on many occasions, and I would have thought that you would have worked out by now that I am not intimidated by you. But then again, maybe your brain is either so faulty, so drug-rotted, or so alcohol-soaked that you can't remember from one day to the next who you have already unsuccessfully had a go at. Go get some help. Seriously. And, unless anyone else has got any sensible comments or questions, I'm done with this now. The amp is fixed. I'm reasonably happy that there are no further issues, and it will be returned to its owner today. Arfa ... Phil |
#16
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Update on the Fender ...
Arfa Daily wrote:
So, the nonsense bias board arrived. ** The "nonsense" is all coming from you - ****head. The board is a nonsense piece of design. ** No it is not. So, would that be more or less so than your opinion of the HK board ** The HK auto bias works fine and is very useful - as I explained in the earlier thread. All water off a ****wit's back to you, I see. ** FFS - there is nothing improper about the set you have. I didn't say that there WAS. ** You did, three or four times. Err, no, I didn't ... ** A damn liar and a ****wit. Typical pommy troll. ** Sheer, paranoid fear of the new. Oh **** off back under your stone you obnoxious arsehole. I've been in this game for 45 years. Nothing has come along in that time to make me paranoid, and this isn't going to be the first ** Stupidity and ASD are all you need to become paranoid. If the design was that fragile, there would be constant PCB failure. You will find there is a very high resistance between the output valve grids and the bias PCB circuitry and the cathode resistors are protected from over-current too. There is a couple of hundred k. Hardly a "very high resistance". ** How many mA does that limit the worst case current to ? What a ****wit, pommy dickhead. Not even honest enough to use his real name. ..... Phil |
#17
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Update on the Fender ...
"Phil Allison" wrote in message ... Arfa Daily wrote: So, the nonsense bias board arrived. ** The "nonsense" is all coming from you - ****head. The board is a nonsense piece of design. ** No it is not. So, would that be more or less so than your opinion of the HK board ** The HK auto bias works fine and is very useful - as I explained in the earlier thread. All water off a ****wit's back to you, I see. ** FFS - there is nothing improper about the set you have. I didn't say that there WAS. ** You did, three or four times. Err, no, I didn't ... ** A damn liar and a ****wit. Typical pommy troll. ** Sheer, paranoid fear of the new. Oh **** off back under your stone you obnoxious arsehole. I've been in this game for 45 years. Nothing has come along in that time to make me paranoid, and this isn't going to be the first ** Stupidity and ASD are all you need to become paranoid. If the design was that fragile, there would be constant PCB failure. You will find there is a very high resistance between the output valve grids and the bias PCB circuitry and the cathode resistors are protected from over-current too. There is a couple of hundred k. Hardly a "very high resistance". ** How many mA does that limit the worst case current to ? What a ****wit, pommy dickhead. Not even honest enough to use his real name. .... Phil snip snip rant rant. Ever the predictable sheep-shagging loony-toon ... Arfa |
#18
Posted to sci.electronics.repair
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Update on the Fender ...
On Tue, 18 Nov 2014 23:22:09 -0500, "Tom Miller"
wrote: "Arfa Daily" wrote in message news "Tom Miller" wrote in message ... "Arfa Daily" wrote in message ... Arfa Useless bloody thunderbird, I remember reading the original of this story but cannot now find it or could you at least repeat the model number. What was the failure in the board, could you tell whether over-current or over-voltage, any deliberate track thinnings for tell-tales. It's a Supersonic 100 head. The board failed to produce any 'controlled' bias to the valves, and all four grids were at -89 volts. It looks as though it works by measuring the voltage across four low value Rs in the cathodes by using A-D inputs on the microcontroller on the board. The bias is then produced by feeding PWM signals from four port pins to driver transistors followed by filter caps. In the case of this board, the supply volts, reset pin etc were all at correct levels, but the micro did not produce any output. You could not even measure any clock at the xtal pins. No evidence of any cause was visible. Board was pristine. Double sided surface mount, and all examined under strong magnification, but no signs of any damaged components. Arfa Any numbers on the cpu? STM32F 101C6 This appears to agree with what it says on the schematic Arfa Put this whole number in a search to get the datasheet. STM32F101C6 It is an ARM Cortex 32 bit CPU with 32k bytes of flash. I don't know how successful you would be copying the firmware over to a new chip.. Believable. I wonder if the crystal itself died. Might check that failure mode out if you are interested. ?-) |
#19
Posted to sci.electronics.repair
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Update on the Fender ...
"josephkk" wrote in message ... On Tue, 18 Nov 2014 23:22:09 -0500, "Tom Miller" wrote: "Arfa Daily" wrote in message news "Tom Miller" wrote in message ... "Arfa Daily" wrote in message ... Arfa Useless bloody thunderbird, I remember reading the original of this story but cannot now find it or could you at least repeat the model number. What was the failure in the board, could you tell whether over-current or over-voltage, any deliberate track thinnings for tell-tales. It's a Supersonic 100 head. The board failed to produce any 'controlled' bias to the valves, and all four grids were at -89 volts. It looks as though it works by measuring the voltage across four low value Rs in the cathodes by using A-D inputs on the microcontroller on the board. The bias is then produced by feeding PWM signals from four port pins to driver transistors followed by filter caps. In the case of this board, the supply volts, reset pin etc were all at correct levels, but the micro did not produce any output. You could not even measure any clock at the xtal pins. No evidence of any cause was visible. Board was pristine. Double sided surface mount, and all examined under strong magnification, but no signs of any damaged components. Arfa Any numbers on the cpu? STM32F 101C6 This appears to agree with what it says on the schematic Arfa Put this whole number in a search to get the datasheet. STM32F101C6 It is an ARM Cortex 32 bit CPU with 32k bytes of flash. I don't know how successful you would be copying the firmware over to a new chip.. Believable. I wonder if the crystal itself died. Might check that failure mode out if you are interested. ?-) I did consider the xtal itself being at fault, but as Fender were sending a new board out to us, I couldn't be bothered at the time to check. I still have the board, so might stick some power on it and see if I can prove anything. Arfa |
#20
Posted to sci.electronics.repair
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Update on the Fender ...
I also bet the crystal or its associated caps (if any). Another bet would be some residual resine or PCB protector turning conductive with age.
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