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SX-1980 Power Supply Board

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BSPAudio

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I've been reading previous threads about the new power supply boards that are being made for the 1980. I've only been able to find 1 person selling them on Ebay. SX-1980 AWR-154

Is this pretty much the way to go or should I be looking at other methods?

My current board is having issues and I'm noticing there is some trace lifting from heat.

Thanks!
 
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I had a 1980 which had burnt traces and burn marks on the power supply board. I redid the dead traces using point to point wires, installed all new transistors and caps and moved the hot transistors to the main heatsinks using mods that are well documented on this site Doing so should result in a board that is reliable for many years after and maintain the original look (if that is important to you). But going the new board method is certainly an attractive solution although I'd keep the old board in case a collector ever wants to make it all-original.
 
I ordered the new board but my plan is to get the existing board up and running. I will definitely keep the old board in case I ever decide to sell it.

Little back story.... While listening to some music I lost all power to the receiver. Did some inspection and found the issues with the board. I haven't dug in too deep, but I did check all the fuses and they are fine. Seems the transformer isn't getting power. Just need to review the schematics to see where the issue lies.
 
I don't have any vintage amplifier or receiver in my collection that gets near an SX-1980 in size and power, but I think it is a good investment to upgrade its power supply from that reputable and reliable source mentioned here. Also, I have seen a recent clip on adding external fans to a large vintage amp. Here it is for those interested.

The Silent Killer of Vintage Stereo Equipment
 
Seems the transformer isn't getting power. Just need to review the schematics to see where the issue lies.
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Depends on the model.
Soft-start thermal fuse open? The unregulated 109VDC drives the relay
 

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This might be TF1? I have 120v on one side and 0 on the other. I can’t zoom in enough on my schematic to confirm if that is TF1 but I believe it is.

IMG_6368.jpeg
 
Yes the thermal fuse sits under and in contact with the soft-start resistor, they are in series.
Test the thermal fuse with the ohmmeter, either they are open (failed,bad) or short(good). Test the soft-start resistor, KC/KU 120V only models are 3R3. Use a small ice pack in contact with body and lead when soldering the thermal fuse, since they are very sensitive to heat from the iron.
 
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The thermal fuse is open. I get 7.2 ohms on the white resistor while still on the board. I can pull it off an see what I get. I think its supposed to be 3.3 ohms.

The overheated part of the board is where there is 2 small resistors coupled together. I can't identify that location on my schematic because it gets too blurry when I zoom in. I'll have to look for another copy.
 
I’ve bought and installed five of the new board and it’s a no brainer, incredible piece of engineering. The old board is horrible.
 
ivandezande said:
I’ve bought and installed five of the new board and it’s a no brainer, incredible piece of engineering. The old board is horrible.
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I have the new one ordered but its probably a month out. Just having a little fun troubleshooting this one. I'd like to get it back up and running before I get the new board just so I know that everything else is working.
 
Installed the new thermal fuse. Everything powered up and worked correctly for about 2 hours then it blew again when I had the volume on the louder side. But the good news is that all functions of the receiver seemed to work perfect in the 2 hours. I'm more confident that once I install the new board I won't have to go troubleshooting too many other issues.

My thinking is that the power is still routed through the soft start resistor (that sits on top of the thermal fuse) instead of switching over causing the resistor to heat up when there is a larger load. This is probably do to the lifted trace and overheating in the area of the coupled resistors that sit just below the 2 relays. I probably need to run some wiring to replace those trace areas.

Looks like my new board has been shipped. I guess we will see how long it takes in transit with all these tariff things going on.
 
You can track the shipment, should not be any delays due to tariffs. If it was sent FedEx then yes they have sat on deliveries. That's why we do not use FedEx anymore. You'll notice how many hands it goes through using the eBay global shipping program. Could be a couple of weeks from past history.
 
rcs16 said:
You can track the shipment, should not be any delays due to tariffs. If it was sent FedEx then yes they have sat on deliveries. That's why we do not use FedEx anymore. You'll notice how many hands it goes through using the eBay global shipping program. Could be a couple of weeks from past history.
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Thank you! Looking forward to getting it. Ebay shows it's still a couple weeks out.
 
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