If you give me voltages, perhaps I can. Whatever, I will give you a clue, I played around all circuit in NAP. Some like your problem, I can say that, there were NO transistors fault. One problem was dead zener and dead resistor and I don't remember but there is a problem in main power supply.
Main power supply, disconnect CZ48 and measure voltage +46 and -46 volt. Is it?
IF CZ46 is a socket. disconnect and measure if it's +37&-37V and there is 5.5 volt.
IF voltages are ok then start to look circuit for zeners, diodes or resistors.
For example R130&R230&R131&R231 must be really hot? R45&R46 must be hot also.
Protection circuit IC44 has some voltages on it (in service manuel), did you measured them?
One addition; In voltages, when amp. is getting hot, voltages changes and increase. If there is less voltage somewhere, after 5 minutes amp. can start to run.
Main power supply, disconnect CZ48 and measure voltage +46 and -46 volt. Is it?
IF CZ46 is a socket. disconnect and measure if it's +37&-37V and there is 5.5 volt.
IF voltages are ok then start to look circuit for zeners, diodes or resistors.
For example R130&R230&R131&R231 must be really hot? R45&R46 must be hot also.
Protection circuit IC44 has some voltages on it (in service manuel), did you measured them?
One addition; In voltages, when amp. is getting hot, voltages changes and increase. If there is less voltage somewhere, after 5 minutes amp. can start to run.
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Thanks.
The fact that the amp will eventually power up leads me to think that the fusible's are okay, but I'm more than happy to be proved wrong on that.
I'm going to replace the 220uF/63v rail cap's as a matter of course as they are close to the heat, and probably not in good shape as a result, and I'll also check the zenner's and fusible's while I'm at it, and hopefully I'll get some idea of where the problem lies.🙂
Thanks.
I'm going to check do some further checks (post above) and if that still doesn't reveal the fault then I'm going to start from scratch, and write everything down this time.
So...
Last night I replaced all 8 of the 220uF/63v caps and powered up; the fault is still present.
When I get home from work I'm going to start from scratch and see if I can work this out.
Last night I replaced all 8 of the 220uF/63v caps and powered up; the fault is still present.
When I get home from work I'm going to start from scratch and see if I can work this out.
Yes Zebra100 , this isn't some multi stage power amplifier that I have seen in EW if a designer wants to show what he can do with a circuit stretching a full page or two .
Take your time --a step at a time --eliminate then carry on from one end to the other.
Take your time --a step at a time --eliminate then carry on from one end to the other.
Electronics World - Wikipedia
I have yearly bound volumes from 1915 up until 1947 including Arthur C.Clarke,s postulation the geocentric satellites could be used for communications .
Its a "serious " electronics magazine and I am surprised somebody living in the UK connected to electronics doesn't know about it .
All D.Self articles and JLH ones are in it as if they wanted to be taken seriously they contributed articles ,I still have many monthly editions but the USA has an excellent website that holds most editions .
WIRELESS WORLD: UK technical magazine 1913-2008
I have yearly bound volumes from 1915 up until 1947 including Arthur C.Clarke,s postulation the geocentric satellites could be used for communications .
Its a "serious " electronics magazine and I am surprised somebody living in the UK connected to electronics doesn't know about it .
All D.Self articles and JLH ones are in it as if they wanted to be taken seriously they contributed articles ,I still have many monthly editions but the USA has an excellent website that holds most editions .
WIRELESS WORLD: UK technical magazine 1913-2008
Ah, EW means something else to me. 😉
Sounds like an interesting publication. I'm more familiar with Hughes Electrical and Electronic theory (Hughes Electrical and Electronic Technology: Amazon.co.uk: Hughes, Edward, Hiley, John, McKenzie-Smith, Ian, Brown, Keith: 9781292093048: Books) although the version I learned from was about thirty years older than the current one.
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So...
Update:
PSU voltages all okay.
Voltages at D11/12 are 4.8 & 4.38v respectively. In comparison D21/22 are rock solid at 4.7v.
R127, marked as 2k7 are actually banded as 3k3. I can't get a good reading across them so my intention was to take them out to confirm resistance, but I did some further checks in the mean time and upon on scoping the base of Q111 I must have disturbed something because when I switched on the amp sprang into life and is now stable.
Next job is to resolder Q111/113/116 which are mounted on the same heatsink, and see where we go from there. Hopefully something simple as a dry joint which Mooly mentioned a few pages back. 😱
Update:
PSU voltages all okay.
Voltages at D11/12 are 4.8 & 4.38v respectively. In comparison D21/22 are rock solid at 4.7v.
R127, marked as 2k7 are actually banded as 3k3. I can't get a good reading across them so my intention was to take them out to confirm resistance, but I did some further checks in the mean time and upon on scoping the base of Q111 I must have disturbed something because when I switched on the amp sprang into life and is now stable.
Next job is to resolder Q111/113/116 which are mounted on the same heatsink, and see where we go from there. Hopefully something simple as a dry joint which Mooly mentioned a few pages back. 😱
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4.38v is not normal. But, the problem may be dry joint. You can control/test hot resistors connection 
Still not fixed...
I haven't got a lot of time to devote to this amp at the moment so I'm having to work on it when I get the chance. High ambient temperature not helping.
I haven't got a lot of time to devote to this amp at the moment so I'm having to work on it when I get the chance. High ambient temperature not helping.
Hi, I recently acquired a "for parts" C325BEE which is now repaired and operates nicely (but no remote control yet in my possession 🙄).
There was a lot wrong with my C325.
Anyway, stumbled onto your thread reading where your riser PCB CB11 is warm? The PCBs in mine each had failed electrolytic caps. These used SMD form factor capacitors. Not certain if the C320 uses SMD.
In addition the power supply circuit for the +18V/-18V was messed up as well. Cap failure here plus broken solder connections, (physically loose) resistors.
I had other major failures that yours evidently does not (I did not [dare not] power up until after complete disassembly, repair of power board, repair of power PCB wire harness, removal and repair of the riser PCBs then reassembly).
Lastly I would concentrate on the ISC circuit as well (caps, resistors and solder connections).
Good luck,
--Joe
There was a lot wrong with my C325.
Anyway, stumbled onto your thread reading where your riser PCB CB11 is warm? The PCBs in mine each had failed electrolytic caps. These used SMD form factor capacitors. Not certain if the C320 uses SMD.
In addition the power supply circuit for the +18V/-18V was messed up as well. Cap failure here plus broken solder connections, (physically loose) resistors.
I had other major failures that yours evidently does not (I did not [dare not] power up until after complete disassembly, repair of power board, repair of power PCB wire harness, removal and repair of the riser PCBs then reassembly).
Lastly I would concentrate on the ISC circuit as well (caps, resistors and solder connections).
Good luck,
--Joe
One more thing, service manuel there are ADJUSTMENT POINT DIAGRAM, if you don't make this adjustments, if the voltage values are out of range, protection circuit, may close the system; red light.
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Thanks.
I'm going to have another crack at this if I get chance this week. I can get the amp to operate 'normally' if I switch on and power up, then leave the red light on for a couple of minutes then reset.
The only adjustments I have in the service manual are DC offset and bias current. There are no projection circuit adjustments. If you have them it would be really useful.🙂
Did you adjust DC offset and bias current? After 5-10 min. values changing , be carefull. And at startup values may be too big. if it's greater than 200mA. it's not good.
In c_320bee.pdf service manuel, it's written voltages on protection circuit. you can check them.
What is your 18 volt voltage value? 18.5v? plus and minus values?
In c_320bee.pdf service manuel, it's written voltages on protection circuit. you can check them.
What is your 18 volt voltage value? 18.5v? plus and minus values?