Sony XM-10020 repair

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hey there,

picked up a Sony XM-10020 on a hunch that it was possibly not working and unfortunately I was right. Had luck fixing another amp recently so giving it another go. Having fun so far looking through the service manual and BCAE and learning a little as I go. Thank for the help

Using a 12v power supply the center leg of the supply FET's is 12.0v. The Rectifier Diode (D305, D306) on the outside legs all have 5.8Vdc. The center leg on D305 has 25.9Vdc, and the D306 has 37.8Vdc. The voltages I am reading are the positive B+ and negative B- rail voltages? Which should be +-40 respectively? I am not sure where to go next, are the rectifier diodes bad?
The data for the values on the IC302 (uPC494C) is way different than the measurements I took.


Pin 1: 0.0
Pin 2: 0.5
Pin 3: 5.0
Pin 4: 5.0
Pin 5: 11.7
Pin 6: 11.7
Pin 7: 4.1
Pin 8: 4.1
Pin 9: 11.2
Pin 10: 0.0
Pin 11: 3.7
Pin 12: 1.7
Pin 13: 0.8
Pin 14: 0.1
Pin 15: 0.5
Pin 16: 0.0


Pin 1: 0
Pin 2: 0.4
Pin 3: 0.1
Pin 4: 0.8
Pin 5: 1.6
Pin 6: 3.7
Pin 7:
Pin 8: 14.4
Pin 9: 4.9
Pin 10: 4.9
Pin 11: 14.4
Pin 12: 14.4
Pin 13:
Pin 14: 5
Pin 15: 0.4
Pin 16: 0


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That's much better, went off the schematic drawing for the pin out. The IC is clearly numbered on the board but I did not catch it, thanks again for the help

OK, on the rectifier diodes center legs secondary voltage are both 30.1Vdc, the outer legs all are 0.0Vdc

Pin 1: 0.0
Pin 2: 0.5
Pin 3: 0.1
Pin 4: 0.8
Pin 5: 1.7
Pin 6: 3.7
Pin 7: 0.0
Pin 8: 11.2
Pin 9: 4.1
Pin 10: 4.1
Pin 11: 11.7
Pin 12: 11.7
Pin 13: 5.0
Pin 14: 5.0
Pin 15: 0.5
Pin 16: 0.0
thanks, this is where I ended up tonight , checking output transistors

When checking transistors (bipolar or FET) with your meter set to ohms, you should not read anything near 0 ohms when the probes are touched to the terminals of any individual transistor in any configuration. If any are shorted (~0 ohms between any 2 legs of any individual transistor), they will likely be shorted from leg 2 to leg 3 but you should check 1-2, 1-3 and 2-3.

the smaller transistors 2SA1358 and 2SC3421 all legs any combo have readings greater than 0 and no O.L which all should be good?

the larger transistors (2SA1671, 2sc4386) which part numbers have them labeled as bipolar transistors in google search don't test out the same way. Across the first two legs, the meter in ohms reads O.L, and the probe config is reversed on the different resistor models. Not sure how to say it so I drew a picture to illustrate.
I need you to find why your meter was reading positive on both rectifiers. That should not be possible and could cause problems later. If you read across the B+ and ground on your amp with the proper polarity, you should read approximately +12v but when you reverse the probes, you should read negative voltage. Do you read negative voltage or does you meter still read positive voltage?

I doubt that there is a problem with the output transistors (without looking at what you posted when checking them). When the output transistors fail, they typically short causing the amp to shut down.
Once again, sir, you are a genius and me, not so much. I stand corrected the D306 rectifier is indeed negative voltage while the other is positive.

so if rail voltage is good, and output transistors most likely ok, I should the check then check input board?

thanks for your time
Do you have either positive or negative rail voltage on the center legs of all outputs and 1v or less on all of the rest of the legs?

Have you tried adjusting the gain with a signal source connected to see if audio ever played through?

Did you use a signal source with a grounded shield or did you use something like a cellphone?
D208, D108 part 2sc3421, DO NOT have +-30Vdc, the voltages across the legs from left to right are -1.2, +1.2, -0.6 on both transistors.

All the other output transistors test out as described.

I use a JVC head unit with a cheap RCA for the source. I can make an RCA with a grounded shield if that will be beneficial, only ground one side correct?

When I turned up the gain the very little output I had disappeared. I was just messing with the input board, supposed to have +15vdc and -15vdc, I didn't write down the readings but the positive was close. The negative was about half of the positive and when I turned up the gain the negative voltage dropped to around -1.2vdc. I did notice an IC301-2 on the input board which looks pretty rough. Going after the schematic to see if I can find the voltages
yes same power supply

resistance right shield RCA head unit to right ground terminal on amp is 0.3

resistance on left fluctuate and climbed from 40 to 180 and kept going bounce to 300 then down to 180 and climb

Q113 -0.5, -30.2, 0.0(+0.1)
Q114 +0.6, +32.9, 0.0(+0.1)

check this out IC301-2
Pin 1: +13.3
Pin 2: +7.8
Pin 3: +7.8
Pin 4: +8.5
Pin 5: +7.5
Pin 6:+7.6
Pin 7:+13.3
Pin 8: +14.2

voltages on the schematic are
Pin 1: 0.0
Pin 2: 0.0
Pin 3: 0.0
Pin 4: -14.5
Pin 5: 0.0
Pin 6: 0.0
Pin 7: 0.0
Pin 8: +14.5
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