Recently acquired sx-1080 is a mess inside/ need a lot of help on this one

Jefferylu98

Active Member
hello again all, I recently picked up a 1080 on the cheep that is at least a 9 on the outside and clean as a whistle inside, but it has many issues inside. I believe this has went across somebody's bench at some time. Owner said it don't work and he don't know anything about it. Lol. Here are the issues I found after a good visual inspection.(I have not plugged this unit in either) both amp boards unplugged-rear jumpers missing- right amp board has burnt r15-looks like a newer q5 in same board-missing pa1001a chip on tuner board(ouch) and the protection board has been pulled away from the plastic holders but looks intact. I need to know where to start on this basket case. I may have a downer board from a smaller model for the chip. This one may never sing again. Fingers crossed. Thanks guys for any input
 
I would start by checking the output transistors. If they are bad, it may determine if you want to go further since they are unobtainable and requires a major work around to replace them.

It has been awhile since I checked them but they are unique with four terminals including two collectors (one is the case). I don't remember the layout of the pins but you can perform simple diode tests. Maybe someone will chime in or you can search the web for the layout.

Fingers crossed, good luck!
 
The Output Transistor work around isn't that bad. Get the service manual.
They are NOT the 4 pin transistor cases found on the sx-1980 and sx-1280, but rather clamped down batwing cases with a BCE layout.
The replacement's cases need different clamp bars. I have documented them somewhere in the forum. I'm looking for it, but a LOT of
pictures have not survived over the years.


That PA1001a is the stereo decoder chip and isn't hard to obtain from a plethora of donor models.
It's the PA1002 that is found only on TOTL models and harder to source.
 
I have a dim bulb tester already, should I start at the power supply first and work my way thru this thing??
 
if it works yes, but its generally considered to be best practice to repair whats wrong with it first. i would check the power supply voltages. but does it pass the dim bulb test? and if it does does come out of protection?
 
Ok, I plugged this baby in to a dbt and I have zero anything, DOA. I checked the fuse in the back of the multi voltage switch and that is good and I checked all the fuses on the psb and thy are good. NOW WHAT??
 
Ok I finally got off the overtime at work and have some time to look at this mess. I have ac power to the main power switch and to pin 13 on the protection board when switched to on, but no power to pin 14 after the relay also pin 12 has 0 power. This thing is dead. Lol. Thanks for any input at this point. I am using a dbt.
 
Study the schematic, follow the flow, this model has a soft start ckt, current passes through the big 20W R to the transformer primary windings. This is for a very short period of time until the DC reg supplies come up and close the relay which shorts out the big 20W R. if the PS does not come up to proper V to close the relay, this is a fault condition, the big 20W R heats up, there is a safety feature, a thermal fuse attached to the big R that is wired in series, it will open if this fault condition occurs. It could be a fuse for the DC supplies. It could be afaulty PS, if so you have to check these things to fix if this is the issue, the thermal fuse has to be checked/replaced and you have to re-build the PS if that is it, so that the +60VDC ckt works and can power the S/S relay.
 
Ok, I think I found an issue, the 20 w cement resistor on the protection board has flew the coop I believe. I pulled it out of circuit and it reads .624m ohms. Should be 3.3k ohms?? I checked the thermal fuse (out of circuit) and it passes current just fine, so I think that is ok. Any ideas for a replacement for cement block resistor? I guess this a start at least. Thanks for any and all help.
 
Btw = this model has the multi voltage dial and I can’t find the correct schematics for the psb and protection board. It’s a little different from the standard schematics
 
Ok, I have a little update. I installed the 3.3k ohm cement resistor and nothing. I jumpered the thermal fuse under the cement resistor and the relay activated. Yeeha, but then the above mentioned Burt resistors on the right amp board started the the white smoking. They are r-14 and 15 on the right amp board. Btw, q5 looks like a newer one as well as the resistors are not original. Done for the night. I’ll have to look at the schematic tomorrow. Any input would be great as to the next move.. thanks in advance
 
That 20 Watt resistor in the soft start circuit is 3.3 ohms not 3.3K ohms. Also don't leave the thermal fuse bypassed after your trouble-shooting is done, replace it if it is bad. It s a fire hazard if the soft start relay does not close with that thermal fuse bypassed.
 
The thermal fuse (105C) must be in contact with the 3R3/20W for the circuit to be safe. the new pcb's, have the R sitting on top of the TF, older ones have it touching with high temp/non-combustible material
 
Yikes. I am picking up a 1080 tomorrow, but reading this is making me scratch my head. The one I'm buying is working as it should, but it hasn't had a major service/shop. Reading this thread reminds me of that Tom Hanks movie, The Money Pit.
 
Merry Xmas everybody. Ok I replaced the the thermal fuse and the cement resistor with the correct one 3.3 ohm. I have the same results as before. R 14/15 start smoking (right amp board). Pulled them out and they tested right at 150 ohms but are burnt also pulled q5 as it was obviously been replaced . Left amp board looks just fine. Somebody has defiantly been on this right amp board playing around. Not sure which way to go with this now. Please help with direction forward. Thanks and have a great holidays.
 
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