Help me with a blown diode please, SX-1500TD

[ranukic]

Hi, I am trying to revive an oldie but goodie. It had been sitting in storage for about 30 years so I blew out the dust and bugs, followed the DeOxit sticky and let it stand about 6 hours. I plugged it in and noticed some scratchy distortion in the audio output, also very weak. I did some more searching and found this diode (pictured) disconnected on the W16-026 Power Supply Unit. I have a board coming that I found on Ebay but I am concerned that something further down the line may be the issue. I have the schematic downloaded but it doesn't have reference signals for me to use my meter on. Has anyone ever run into this or does anyone have a suggestion on where I should look? Also, would this diode cause the audio issue I described? I assume that the power isn't being distributed properly through the amp.

Thanks,
James

 

[petehall347]

those 4 diodes are the main bridge rectifier . they all need changing for suitable subs .
you could be lucky and find its the only fault .
there are fuses on the main amp board which should have blown if there is a short there . be worth checking if they are the correct values .

 

[petehall347]

are the diodes marked 1s1073 ?

 

[ranukic]

Yes that is the number on them.

 

[ranukic]

those 4 diodes are the main bridge rectifier . they all need changing for suitable subs .
you could be lucky and find its the only fault .
there are fuses on the main amp board which should have blown if there is a short there . be worth checking if they are the correct values .

Good thinking. I just assumed they were.

 

[petehall347]

something like 1N5404 should be a replacement .
look up the data sheets to be sure .

 

[ranukic]

I received the power supply board and soldered it in. Fired it up and it was garbled and waved in and out for a couple of minutes then it smoothed out and sounded really awesome. I hooked up a bluetooth device in through the aux channel, switched through from A to B to A+B, and the pots and buttons were smooth without distortion. The only button that does not seem to work is the mute.

During the first couple of minutes I noticed the FM tuner seemed to be slightly overlapping stations and would not display the stereo light. After it cleared up the stereo tuned nicely with zero overlap.

 

[ranukic]

It happened again tonight. I started playing around with the loudness button and noticed that the it seems to be the cause of the sound fluctuation. So I ordered a replacement board from the same guy who sent me the power supply board. The mute button wasn't working either and since it was on the same circuit board I hopefully am taking care of two problems in one. I ordered new LED fuse lamps for the tuner display so once I have those and as long as the board fixes my sound issue I can button this back up.

The case is in good structure shape so I plan to get some new maple veneer and do my best to match the finish. Does anyone have experience staining fresh veneer so that it matches existing?

Thanks,
James

 

[rcs16]

I thought that Pioneer usually used walnut as it cases veneer species, not maple. if you use maple then use a walnut stain, try on a sample piece to match it up.

 

[ranukic]

I will double check. I thought I had read maple but that may have been my speaker box that I was reading about.

 

[ranukic]

Hey,

Still tinkering but yesterday I noticed that the issue I mentioned earlier regarding the garble/static sound happens bad on Phono 1, phono 2 and just ok on FM. Aux and tape sound perfect.

Any ideas?
Thanks,

James

 

[petehall347]

might be function switch or tape monitor switch if it has one

 

[ranukic]

I forgot to mention that the stereo light has stopped lighting when FM channels are tuned in. The bulb is still good just no signal.

 

[ranukic]

might be function switch or tape monitor switch if it has one

I was using the tape monitor switch with my bluetooth device and it was clear. The rotary selector switch has been cleaned with deoxit d5 and lubed with g5. The whole amp has been cleaned with deoxit.

 

[petehall347]

check if phono board is getting the correct power from supply

 

[ranukic]

Thanks. I was looking through the schematics this morning to try and find the path that Tape and Aux travel through the amp versus FM/Phono 1&2. The problem either lies there or as you suggested above maybe the power supplied to the boards is weak. I will check the power supply output tonight, I was looking for the voltage outputs on the power supply and just found them this morning in the schematics.

Again thank you for the suggestions.

James

 

[ranukic]

Hey,

I am slowly recapping this but I just noticed that the manual for this amp shows a W13-024 p/n for the MPX unit and my amp had a W13-026 MPX unit. The best I can come up with is the manual from the SX-6000 for a schematic. The layout appears the same but I am not sure if the cap sizes are correct. Unfortunatley I had pulled all of the caps so I can't compare what was on the unit to the manual. Any suggestions?
Thanks,
James

 

[petehall347]

sx-1500td-s.pdf .is what mine is labelled as and has the 026 board in it .. i dont know where i got it from .but it would have been a free download .

 

[petehall347]

 

[petehall347]