Hi Guys & Gals,
I have an Onkyo M-508 that I'm trying to fix. Symptoms are it will come up in Protection mode, then switch to Play mode, and then about a minute later, go back into Protection and stay there. I've pulled all 8 of the power supply caps, and on average, they are about 12% below their 10,000uf value. From repairing many 1000's of pieces of equipment in my 60+ years of audio repair, I know this 12% isn't causing the problem.
1. Cannot adjust bias on either channel, and neither channel heats up.
2. Rails measure funny, which is why I spent 4 hours removing the caps. It has separate transformers, bridge rectifiers, and 4 caps for each channel. Rails supposed to be +75 and -75. One channel, rails are +73 & -83. Other channel not as bad, something like 73 & 78.
3. Dissembled enough to check the two bridge rectifiers in circuit, and all diodes are there.
This unit has "LED voltage regulators", LTZ-15R, that look like fat 1N4148's. They are being used, along with dropping resistors, to get a lower value DC for the input & driver transistors. Some of those, in the same circuit position of both channels, do NOT glow, because there isn't enough voltage to light them up. I've checking dropping resistors.
Next thing I will do is make the decision about re-capping the PS caps, IF I can find a suitable substitute for the Nichicon 10000uf/90v caps in the unit.
The fact that both channels are affected led me to PS problems, but thats not it.
Thanks for reading !!
ANY IDEAS ??
I have an Onkyo M-508 that I'm trying to fix. Symptoms are it will come up in Protection mode, then switch to Play mode, and then about a minute later, go back into Protection and stay there. I've pulled all 8 of the power supply caps, and on average, they are about 12% below their 10,000uf value. From repairing many 1000's of pieces of equipment in my 60+ years of audio repair, I know this 12% isn't causing the problem.
1. Cannot adjust bias on either channel, and neither channel heats up.
2. Rails measure funny, which is why I spent 4 hours removing the caps. It has separate transformers, bridge rectifiers, and 4 caps for each channel. Rails supposed to be +75 and -75. One channel, rails are +73 & -83. Other channel not as bad, something like 73 & 78.
3. Dissembled enough to check the two bridge rectifiers in circuit, and all diodes are there.
This unit has "LED voltage regulators", LTZ-15R, that look like fat 1N4148's. They are being used, along with dropping resistors, to get a lower value DC for the input & driver transistors. Some of those, in the same circuit position of both channels, do NOT glow, because there isn't enough voltage to light them up. I've checking dropping resistors.
Next thing I will do is make the decision about re-capping the PS caps, IF I can find a suitable substitute for the Nichicon 10000uf/90v caps in the unit.
The fact that both channels are affected led me to PS problems, but thats not it.
Thanks for reading !!
ANY IDEAS ??