Pioneer SX-3400 distorted sound
- Thread starter ThePlague
- Start date
petehall347
the brandy coffee man
supply might be failing under load
petehall347
the brandy coffee man
its rebuild-able if found its needed .
will see if i can figure out some things to check .
in the meantime have a look at all solder connections with a magnifier .
will see if i can figure out some things to check .
in the meantime have a look at all solder connections with a magnifier .
petehall347
the brandy coffee man
just look first .. then redo any that look bad .
Run some wattage into the dummy load speakers (say 8vac) and check the power supply voltages, at C122, C123, Q29 ecb and R129/R130.
If it were just one channel I would be looking for an amplifier fault, but both channels calls for a common fault.
One thing to try FIRST, instead of connecting your dummy loads to the - speaker connections, go to a chassis ground like the phono grounding screw instead. Resistance in that line might be doing something,
It depends upon the internal factory wiring, trace the minus wires back from the terminals to the center tap's chassis ground - pin 3. and the white transformer wire connected to it. Look for bad connections there.
If it were just one channel I would be looking for an amplifier fault, but both channels calls for a common fault.
One thing to try FIRST, instead of connecting your dummy loads to the - speaker connections, go to a chassis ground like the phono grounding screw instead. Resistance in that line might be doing something,
It depends upon the internal factory wiring, trace the minus wires back from the terminals to the center tap's chassis ground - pin 3. and the white transformer wire connected to it. Look for bad connections there.
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ThePlague
Active Member
No change with a different ground. With a dummy load with a good bit of watts going through it, here are my readings.
C122: -29.5v C123: +29.5V Q29 (after R145 there is an inline 75 mA reading on the diagram. At that point of measurement, I am reading 193.6 mA)
R129/R130: +29V.
C122: -29.5v C123: +29.5V Q29 (after R145 there is an inline 75 mA reading on the diagram. At that point of measurement, I am reading 193.6 mA)
R129/R130: +29V.
petehall347
the brandy coffee man
how did you read the 193.6 ma ? just curios more than anything
ThePlague
Active Member
Black probe to chassis ground, Red probe on the top leg of R145 which is the last component connection before the reading mark. If you are looking at the schematic, I probed the right side of R145.
petehall347
the brandy coffee man
i don't understand why you would want to be shorting the supply to the pilot lamp with your meter ...:scratch2:
or why even bother checking unless you suspect lamps are pulling excess current .
now then this is the correct way to measure the current draw ...
measure voltage across 145 146 then use ohms law to work out the current ..
R129 R130 should be negative ..:same as c123 scratch2:
looks to me like your meter is reading backwards ..
or why even bother checking unless you suspect lamps are pulling excess current .
now then this is the correct way to measure the current draw ...
measure voltage across 145 146 then use ohms law to work out the current ..
R129 R130 should be negative ..:same as c123 scratch2:
looks to me like your meter is reading backwards ..
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petehall347
the brandy coffee man
when your meter is set on amps its more or less a short circuit between the leads .. well it wont be on ma setting as it will have a resistor inside and the meter measures volt drop across and shows you in ma on the screen ..
on any amps setting you connect your meter leads in series with the circuit not in parallel .
can you confirm your readings on the other parts ? its just + and - are reversed for some reason which i cant believe .. its important to get these things written down correctly for others finding the thread later when trying a repair .
on any amps setting you connect your meter leads in series with the circuit not in parallel .
can you confirm your readings on the other parts ? its just + and - are reversed for some reason which i cant believe .. its important to get these things written down correctly for others finding the thread later when trying a repair .
ThePlague
Active Member
Oh, I was no aware of that. Any parts in particular you'd like me to confirm my polarity on? Also, to be of note, I just noticed that with my dummy 20w 8ohm resistors hooked up and the volume set to max, I can hear a buzzing sound to the beat of the radio station in the chassis it self. Couldn't quite identify its origin, but not sure if that is normal operation. 
petehall347
the brandy coffee man
are the load resistors hotting up ? i hope so ..
petehall347
the brandy coffee man
no the ones wired to the speaker posts
ThePlague
Active Member
Sorry to revive such an old thread, but I just haven't been able to work on the amp. I have some time now and would like to try again.
With my laser thermometer, The load resistors are at 86.5F after about 10 minutes of running. Not sure if that is considered heating up or not.
With my laser thermometer, The load resistors are at 86.5F after about 10 minutes of running. Not sure if that is considered heating up or not.
