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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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C - Audio slave amp ...
Anybody by any remote chance have a schematic copy for a C - Audio RA 1001
slave amp ? Drawn a blank from all the usual places. Looks as though it has been stored somewhere cold and damp, although dry enough now. Basically, it won't come out of 'protect' although there seems to be nothing wrong fundamentally with either channel. Both channels have good output, with no DC offset, as far as the output relays. There is another relay over at the mains input side of things that looks like it shorts a bloody great resistor, so inrush limiting I guess. All three relays remain stubbornly off, and the protect light stays on. I can't read any volts at any of the three relay coils, and none of the pins appears to be grounded, so they are not high-side switched. So may be something as simple as a missing rail, but hard to follow print around as it's double sided, and fairly crowded ... Arfa |
#2
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C - Audio slave amp ...
Arfa Daily wrote in message
news Anybody by any remote chance have a schematic copy for a C - Audio RA 1001 slave amp ? Drawn a blank from all the usual places. Looks as though it has been stored somewhere cold and damp, although dry enough now. Basically, it won't come out of 'protect' although there seems to be nothing wrong fundamentally with either channel. Both channels have good output, with no DC offset, as far as the output relays. There is another relay over at the mains input side of things that looks like it shorts a bloody great resistor, so inrush limiting I guess. All three relays remain stubbornly off, and the protect light stays on. I can't read any volts at any of the three relay coils, and none of the pins appears to be grounded, so they are not high-side switched. So may be something as simple as a missing rail, but hard to follow print around as it's double sided, and fairly crowded ... Arfa If the C is for Crest then sounds like my experience of a pile of Crest Audio Pulse 2 1100 , amps stored in a Dutch barn schema available out there repair briefs on http://www.divdev.fsnet.co.uk/repair2a.htm IIRC all the problems were condensation/corossion inside minor TO92 owner thought draping a tarpaulin over them in the barn was sufficient protection in the UK |
#3
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C - Audio slave amp ...
"Arfa Daily" wrote in message news Anybody by any remote chance have a schematic copy for a C - Audio RA 1001 slave amp ? Drawn a blank from all the usual places. Looks as though it has been stored somewhere cold and damp, although dry enough now. Basically, it won't come out of 'protect' although there seems to be nothing wrong fundamentally with either channel. Both channels have good output, with no DC offset, as far as the output relays. There is another relay over at the mains input side of things that looks like it shorts a bloody great resistor, so inrush limiting I guess. All three relays remain stubbornly off, and the protect light stays on. I can't read any volts at any of the three relay coils, and none of the pins appears to be grounded, so they are not high-side switched. So may be something as simple as a missing rail, but hard to follow print around as it's double sided, and fairly crowded ... Arfa Check for corroded tracks around the fan area of the PCB, it was a common failure, allegedly from corrosive smoke machine smoke. Folow the relay coil tracks back to the protect circuit at the front of the amp (I think) as ISTR it was often a break in this circuit that kept it in protect. That bloody great resistor is in fact inrush limiting shorted out by a relay, (47 ohms?), and these often failed. I might have a RA3000 schematic at work, will look tomorrow. It is not a Crest. Gareth. |
#4
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C - Audio slave amp ...
"Arfa Daily" wrote in message news Anybody by any remote chance have a schematic copy for a C - Audio RA 1001 slave amp ? Drawn a blank from all the usual places. Looks as though it has been stored somewhere cold and damp, although dry enough now. Basically, it won't come out of 'protect' although there seems to be nothing wrong fundamentally with either channel. Both channels have good output, with no DC offset, as far as the output relays. There is another relay over at the mains input side of things that looks like it shorts a bloody great resistor, so inrush limiting I guess. All three relays remain stubbornly off, and the protect light stays on. I can't read any volts at any of the three relay coils, and none of the pins appears to be grounded, so they are not high-side switched. So may be something as simple as a missing rail, but hard to follow print around as it's double sided, and fairly crowded ... Arfa One corroded track I found was actually underneath one of the relays! You could be right and it might just be the low voltage supply for the protect/relays. If the inrush relay doesn't click in, the output relays won't either, otherwise the inrush resistor would go bang once the amp delivered any power. Gareth. |
#5
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C - Audio slave amp ...
" Nutcase Kook" If the C is for Crest ** No way. "C-Audio" is a British maker. Weird contraptions with a mix of Hitachi power mosfets and Motorola TO3s in the output stages. The fan routinely caused amps to fail since it blew directly onto a bunch of high voltage TO92s and covered them in dust and moisture. .... Phil |
#6
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C - Audio slave amp ...
"Phil Allison" wrote in message ... " Nutcase Kook" If the C is for Crest ** No way. "C-Audio" is a British maker. Weird contraptions with a mix of Hitachi power mosfets and Motorola TO3s in the output stages. The fan routinely caused amps to fail since it blew directly onto a bunch of high voltage TO92s and covered them in dust and moisture. ... Phil Yes indeed. C-Audio were based in Cambridge, and their offerings were quite well regarded in the pro audio field. They are, however, long gone now. This one has only mosfets in the output stages, no TO3s at all. Considering how long they were around, I was very surprised to not find any schematics on the usual sites. Arfa |
#7
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C - Audio slave amp ...
"Gareth Magennis" wrote in message ... "Arfa Daily" wrote in message news Anybody by any remote chance have a schematic copy for a C - Audio RA 1001 slave amp ? Drawn a blank from all the usual places. Looks as though it has been stored somewhere cold and damp, although dry enough now. Basically, it won't come out of 'protect' although there seems to be nothing wrong fundamentally with either channel. Both channels have good output, with no DC offset, as far as the output relays. There is another relay over at the mains input side of things that looks like it shorts a bloody great resistor, so inrush limiting I guess. All three relays remain stubbornly off, and the protect light stays on. I can't read any volts at any of the three relay coils, and none of the pins appears to be grounded, so they are not high-side switched. So may be something as simple as a missing rail, but hard to follow print around as it's double sided, and fairly crowded ... Arfa One corroded track I found was actually underneath one of the relays! You could be right and it might just be the low voltage supply for the protect/relays. If the inrush relay doesn't click in, the output relays won't either, otherwise the inrush resistor would go bang once the amp delivered any power. Gareth. Pretty much as I was figuring then. I'm sure it will be a simple problem when I get to the bottom of it. Just depends how much time the owner is prepared to pay for ... If you have any schematics that are at least similar, it would be appreciated. Most of these amp manufacturers don't reinvent the wheel, and the relay circuitry is quite likely to be similar between models TIA Arfa |
#8
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C - Audio slave amp ...
"Arfa Daily" If you have any schematics that are at least similar, it would be appreciated. Most of these amp manufacturers don't reinvent the wheel, and the relay circuitry is quite likely to be similar between models ** Decades ago, I managed to extract some schems for C-Audio from the Aussie importer ( same people who now make Rode Microphones). Not like normal schems, these were large scale drawings with each part of an amp on a new page - so very had to use in servicing. Chucked them a long while ago. IIRC, the relay system was full of BF422 and BF423 transistors, all sitting right in the fan blast, with badly corroded legs. Check and replace these if needed and that may be all you have to do. .... Phil |
#9
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C - Audio slave amp ...
"Phil Allison" wrote in message ... "Arfa Daily" If you have any schematics that are at least similar, it would be appreciated. Most of these amp manufacturers don't reinvent the wheel, and the relay circuitry is quite likely to be similar between models ** Decades ago, I managed to extract some schems for C-Audio from the Aussie importer ( same people who now make Rode Microphones). Not like normal schems, these were large scale drawings with each part of an amp on a new page - so very had to use in servicing. Chucked them a long while ago. IIRC, the relay system was full of BF422 and BF423 transistors, all sitting right in the fan blast, with badly corroded legs. Check and replace these if needed and that may be all you have to do. .... Phil It was on one of these amps that I replaced BC182's with BC182L,s not realising the pinout was different. It was a week before I worked out what the f**k was going on there. Gareth. |
#10
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C - Audio slave amp ...
"Gareth Magennis" "Phil Allison" ** Decades ago, I managed to extract some schems for C-Audio from the Aussie importer ( same people who now make Rode Microphones). Not like normal schems, these were large scale drawings with each part of an amp on a new page - so very had to use in servicing. Chucked them a long while ago. IIRC, the relay system was full of BF422 and BF423 transistors, all sitting right in the fan blast, with badly corroded legs. Check and replace these if needed and that may be all you have to do. It was on one of these amps that I replaced BC182's with BC182L,s not realising the pinout was different. It was a week before I worked out what the f**k was going on there. ** The BF423 and MPSA92 differ only slightly in specs, but have different pin outs. The BF number having the collector in the middle while the MPSA has the base there. .... Phil |
#11
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C - Audio slave amp ...
"Arfa Daily" wrote in message
... "Gareth Magennis" wrote in message ... "Arfa Daily" wrote in message news Anybody by any remote chance have a schematic copy for a C - Audio RA 1001 slave amp ? Drawn a blank from all the usual places. Looks as though it has been stored somewhere cold and damp, although dry enough now. Basically, it won't come out of 'protect' although there seems to be nothing wrong fundamentally with either channel. Both channels have good output, with no DC offset, as far as the output relays. There is another relay over at the mains input side of things that looks like it shorts a bloody great resistor, so inrush limiting I guess. All three relays remain stubbornly off, and the protect light stays on. I can't read any volts at any of the three relay coils, and none of the pins appears to be grounded, so they are not high-side switched. So may be something as simple as a missing rail, but hard to follow print around as it's double sided, and fairly crowded ... Arfa One corroded track I found was actually underneath one of the relays! You could be right and it might just be the low voltage supply for the protect/relays. If the inrush relay doesn't click in, the output relays won't either, otherwise the inrush resistor would go bang once the amp delivered any power. Gareth. Pretty much as I was figuring then. I'm sure it will be a simple problem when I get to the bottom of it. Just depends how much time the owner is prepared to pay for ... If you have any schematics that are at least similar, it would be appreciated. Most of these amp manufacturers don't reinvent the wheel, and the relay circuitry is quite likely to be similar between models TIA Arfa Just a thought - I have seen on many older amps, a small value electrolytic used to provide a hold-off for the sharp cutoff at power-off. Power shut off, DC (usually 1/2 wave recified) dies very quickly, and protect relay cuts off before the amp can "pop". Usually 1uF, 2.2uF, 4.7uF etc associated with a single diode in the power supply. This is especially common if a TA7317P or similar protect IC is used. Later! Mark Z. |
#12
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C - Audio slave amp ...
Hi,
I've emailed you the 1001/2001/3001 schematics. Sorry for delay, but hours of major outage of BT Internet this morning. Maybe you could post them somewhere when you have time and post a link here, I'm sure there will be a few interested here in having them. I'm not very good at that sort of thing. Note what I said about the 'L' suffix - I got it the wrong way round, but C-Audio used BC184L and BC214L in these designs, and these are a different pinout to BC 184 and BC214. Cheers, Gareth. |
#13
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C - Audio slave amp ...
I did look at uploading the schematics to eserviceinfo, but they want far
too many personal details for registration for my liking. Gareth. |
#14
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C - Audio slave amp ...
"Gareth Magennis" wrote in message ... I did look at uploading the schematics to eserviceinfo, but they want far too many personal details for registration for my liking. Gareth. All received, thanks. I'll try and look into it again by the weekend, and post back. Phil. Did you have a good birthday ? :-) Arfa |
#15
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C - Audio slave amp ...
"Arfa Daily" wrote in message ... "Gareth Magennis" wrote in message ... I did look at uploading the schematics to eserviceinfo, but they want far too many personal details for registration for my liking. Gareth. All received, thanks. I'll try and look into it again by the weekend, and post back. Phil. Did you have a good birthday ? :-) Arfa OK. It's fixed. The three relay coils are in series and are switched by Q45. There was good volts at its emitter, but bugger all at its collector. Conditions at its base were wrong, but not because of it sensing DC offset or over-temp condition, so had to be a component around the transistor. Turned out that the base ground return resistor R148 39k was completely open. No signs of any distress or corrosion, just open. Put a new one in, and away it went, so I was a happy bunny as I reached for the pen to write the bill out ... :-) Cheers for the help with the schems Gareth. It just makes the job so much easier ! Arfa |
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