Hi, I have a Fisher BA-6000 which cosmetically looks very good. When it turns on the relay does not seem to click after the usual initial 2 seconds. A resistor, the R72, burned and carbonized part of the PCB below (tension of aprox 119v in between it). The power supply seems to be working ok (59-0-59v power stage; 64-0-64v preamp; 0-7v meter lamps), and the VU meters move a little when the system starts, so it is a pity this beast does not work.
The upper channel seems to have the right voltages, plus minus some 5% I would say. The bottom channel has problems for sure. The initial voltages seem ok for the first transistors but the farther away from input the more they vary from specs to the point we get 119v in between legs 3-8 of ICO2 when they should be zero (as if legs 2-3 and 8-9 were shorted, or the IC fully turned on). Q18 gets very warm. Does it makes any sense to try to repair this? If so any way to figure out which components are for sure wrong without a lenghty trial and error?
Can I check if the upper channel is ok by connecting a speaker before the relay or will I put at risk a speaker?
I would appreciate any help. thxs, Gus
The upper channel seems to have the right voltages, plus minus some 5% I would say. The bottom channel has problems for sure. The initial voltages seem ok for the first transistors but the farther away from input the more they vary from specs to the point we get 119v in between legs 3-8 of ICO2 when they should be zero (as if legs 2-3 and 8-9 were shorted, or the IC fully turned on). Q18 gets very warm. Does it makes any sense to try to repair this? If so any way to figure out which components are for sure wrong without a lenghty trial and error?
Can I check if the upper channel is ok by connecting a speaker before the relay or will I put at risk a speaker?
I would appreciate any help. thxs, Gus
Attachments
R72 being burnt means the VI limiter on that channel clamped hard on. IC02 will have failed. The relay not coming on means the DC detector is doing its job.
If you want to test the working channel, it should be OK to remove IC02 from the circuit, and the relay should then activate. Unless you are confident you can get genuine STK0010's though (or engineer a replacement!) you wont be able to do much to effect a repair.
If you want to test the working channel, it should be OK to remove IC02 from the circuit, and the relay should then activate. Unless you are confident you can get genuine STK0010's though (or engineer a replacement!) you wont be able to do much to effect a repair.
Today, 05:32 AM
Ian Finch Australia
diyAudio Member
Join Date: Apr 2010
Location: Coffs Harbour
There is no need to connect speakers to measure the fault voltage at the output. The relay does not click because it must not connect the speakers to the amplifier when there is DC present at the output, just as designed, to protect them from the likely voltage when the module or any other conventional AB class amplifier fails. The rail voltages are nominal +/-58VDC, so you are reading the voltage across both power rails. However, the voltage of concern is from the the output terminal to speaker ground voltage, which the speakers otherwise have to cope with.
Now that hybrid audio modules are long obsolete, the replacement parts you buy will most likely be refurbs of unknown, widely varying, hand assembled quality. Were it not for the serious quality problem of using these unknown sources, you might try to resurrect the amplifier.
As it is though, removing the power amplifiers completely and retrofitting discrete amplifier modules, complete or kit form, would be a better and more dependable long-term solution.
__________________
Ian
Ian Finch Australia
diyAudio Member
Join Date: Apr 2010
Location: Coffs Harbour
There is no need to connect speakers to measure the fault voltage at the output. The relay does not click because it must not connect the speakers to the amplifier when there is DC present at the output, just as designed, to protect them from the likely voltage when the module or any other conventional AB class amplifier fails. The rail voltages are nominal +/-58VDC, so you are reading the voltage across both power rails. However, the voltage of concern is from the the output terminal to speaker ground voltage, which the speakers otherwise have to cope with.
Now that hybrid audio modules are long obsolete, the replacement parts you buy will most likely be refurbs of unknown, widely varying, hand assembled quality. Were it not for the serious quality problem of using these unknown sources, you might try to resurrect the amplifier.
As it is though, removing the power amplifiers completely and retrofitting discrete amplifier modules, complete or kit form, would be a better and more dependable long-term solution.
__________________
Ian
That is a copy and paste from,
http://www.diyaudio.com/forums/solid-state/234415-how-did-i-blow-fisher-ba6000-2.html#post4564661
http://www.diyaudio.com/forums/solid-state/234415-how-did-i-blow-fisher-ba6000-2.html#post4564661
Thxs both Ian and Jaycee. I will discard the shorted ICO2 and consider one of the solutions proposed:
i) get a quick $20 replacement from internet
ii) or try to figure out values of resistors and type of diodes and transistors for a discrete longer-term replacement of the STK0100II.
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Gus
i) get a quick $20 replacement from internet
ii) or try to figure out values of resistors and type of diodes and transistors for a discrete longer-term replacement of the STK0100II.
------
Gus
The hybrid module circuit you posted is only representative of the real amplifier and shows no semiconductor die details or resistor values anyway. Don't try to duplicate this in discrete form because you won't have the same thermal or electrical operating conditions as the hybrid.
Replace both amplifiers completely with suitable kits, as suggested earlier, if you want a decent stereo pair of amplifiers.
Replace both amplifiers completely with suitable kits, as suggested earlier, if you want a decent stereo pair of amplifiers.
I had the same problem: R72 (1k) vaporized, D10 as well as D12 shorted and both current limiter transistors completely shorted out throughout.
I replaced them all, the diodes replaced by 1N4148 and the pair of transistors replaced by 2SA965Y / 2SC2235Y and ordered two new STK modules from the German eBay:
Hybrid-IC STK0100II ; Power Audio Amp | eBay
I hope this will work out. I'll of course triple check all surrouding parts and switch the amp on the first time with an incandescent bulb of 100 Watts in series as well as use a variac. I don't want to blow those modules the first 0.1 second after switching the amp on!
The conditions under which this amp blew are mysterious: half an hour ago, it was switched off, then back on again an KABOOM both channels gave way, fuses of 6.3 Amps blew. BOTH STK modules dead shorted on both of their output transistors...
I replaced them all, the diodes replaced by 1N4148 and the pair of transistors replaced by 2SA965Y / 2SC2235Y and ordered two new STK modules from the German eBay:
Hybrid-IC STK0100II ; Power Audio Amp | eBay
I hope this will work out. I'll of course triple check all surrouding parts and switch the amp on the first time with an incandescent bulb of 100 Watts in series as well as use a variac. I don't want to blow those modules the first 0.1 second after switching the amp on!
The conditions under which this amp blew are mysterious: half an hour ago, it was switched off, then back on again an KABOOM both channels gave way, fuses of 6.3 Amps blew. BOTH STK modules dead shorted on both of their output transistors...
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