When I put a 110v65w incandescent bulb in place of removed D15, all opamp pins and rca shields see 2vdc referencing common speaker terminals.
U5-lm317 gets warm after a minute or so
R176 not smoking/hot
What is S11 switch? It’s not described on the back cover.
U5-lm317 gets warm after a minute or so
R176 not smoking/hot
What is S11 switch? It’s not described on the back cover.
Di the negative terminals of the op-amps have -15v?
Is the DC voltage on the op-amps enough to produce low level audio (to possibly find one op-amp that's defective)?
S11 is for the optional bass module. The service manual provides more information.
Is the DC voltage on the op-amps enough to produce low level audio (to possibly find one op-amp that's defective)?
S11 is for the optional bass module. The service manual provides more information.
No but when I do, I get -15.5vdc on pins 11, but only 0.960vdc on pins 4.
U3 opamp outputs -14vdc on pin 12,13,& 14. The rest are all at about 0.2-0.9vdc.
U3 opamp outputs -14vdc on pin 12,13,& 14. The rest are all at about 0.2-0.9vdc.
Yes so I clipped a few legs.
First I clipped leg 14.
Pad measures 0vdc. Output leg of the ic measuring -14vdc.
Pin 13 went to zero
Then I clipped leg 12. The pad is measuring -14vdc and the leg is measuring 0v.
Pin 13 stayed at zero.
First I clipped leg 14.
Pad measures 0vdc. Output leg of the ic measuring -14vdc.
Pin 13 went to zero
Then I clipped leg 12. The pad is measuring -14vdc and the leg is measuring 0v.
Pin 13 stayed at zero.
You mean if D15 is back in circuit? Yes there is still a problem with rail drop, that resistor gets hot, and seems the regs struggle
Cut the power supply pins on that IC.
Look at the diagram attached. Notice that there are two U3B sections. Is it possible that one of these are actually the U3D section with DC on it?
Look at the diagram attached. Notice that there are two U3B sections. Is it possible that one of these are actually the U3D section with DC on it?
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That didn’t help cutting U3 power pins. R176 still hot.
U1 has most pins at +8vdc. Pin 11 at -7.8vdc
U2 same as U1. Mostly +8vdc on pins. Only pin 4 is at -7.8vdc.
U1 has most pins at +8vdc. Pin 11 at -7.8vdc
U2 same as U1. Mostly +8vdc on pins. Only pin 4 is at -7.8vdc.
Yea that diagram is showing U3B with pins 5,6,7. Pin 7 is connected to R78 & R79. I cannot find R74 though.
U3D on the top of the page, for instance pin 12 is connected to R8 which matches the PCB.
I'll put the bulb back in and remove the diode again.
U3D on the top of the page, for instance pin 12 is connected to R8 which matches the PCB.
I'll put the bulb back in and remove the diode again.
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What's the DC voltage on all terminals of U2?
Does the crossover line out switch make a difference in pin 12 being at -14v?
Does the crossover line out switch make a difference in pin 12 being at -14v?
U2 is a 5532
1: -15.4
2: 0.245
3: 1.004
4: -15.4
5: -3.48
6: -3.6
7: 0.35
8: 1.004
The line out crossover switch goes up through the heat sink. It’s a three position switch that doesn’t change the output on U3D pin 12; which stays at -14.9vdc.
1: -15.4
2: 0.245
3: 1.004
4: -15.4
5: -3.48
6: -3.6
7: 0.35
8: 1.004
The line out crossover switch goes up through the heat sink. It’s a three position switch that doesn’t change the output on U3D pin 12; which stays at -14.9vdc.
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If the power supply had normal voltage, that op-amp would definitely be defective unless something was driving voltage back into pin 1.
That said, some op-amps will invert their expected output if one output is driven to one of the supply rails.
One more thing... I've had problems with bad solder connections on the SMD resistors on the preamp input boards in these amps. You may want to check those before you pull U2 to check the voltage on its pads. Don't cut the legs unless you have a replacement.
That said, some op-amps will invert their expected output if one output is driven to one of the supply rails.
One more thing... I've had problems with bad solder connections on the SMD resistors on the preamp input boards in these amps. You may want to check those before you pull U2 to check the voltage on its pads. Don't cut the legs unless you have a replacement.
Maybe I should throw D15 back in and re-test the voltages on U2?
I'll comb through the pre-amp boards.
This amp is frustrating for not having fixed an amp in almost 10 years. I want to use this amp in my personal system. I may toss it as seems the costs to repair are already about $80 in parts. Thank you for helping
I'll comb through the pre-amp boards.
This amp is frustrating for not having fixed an amp in almost 10 years. I want to use this amp in my personal system. I may toss it as seems the costs to repair are already about $80 in parts. Thank you for helping
Finish it out. What's $80 compared to the cost of an equivalent quality amplifier? Not much. It's worth the perseverance.
Thanks. It got kind of late last night and my brain was fading.
I'll see what I can get done later today. I'm thinking of just careful snipping Pin1 leg at the base so that I can test. If its bad its bad. If its OK I should be able to re-solder back on. That might be the quickest way to test this. Other option would be to trace through the schematic and find any faults like a shorted cap or transistor.
I'll see what I can get done later today. I'm thinking of just careful snipping Pin1 leg at the base so that I can test. If its bad its bad. If its OK I should be able to re-solder back on. That might be the quickest way to test this. Other option would be to trace through the schematic and find any faults like a shorted cap or transistor.