sx-1080 Pioneer questions

steamwhistle

steamwhistle

AK Subscriber
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My 1080 overheated recently and stopped playing. I checked everything out and found that one of my Cerwin Vega big guys was 8 ohm and the smaller Cerwin Vega was 4. Thought sure it was an 8. So I recapped and put new transistors in. I turned it on and it played beautifully--for ten minutes. With a little pop, it stopped. It will try to come on again every3 seconds or so, then it will pop off, and try again and again. Of course I have it on the usual lightbulb safety system. The bulb stays dim, and nothing is overheating, but the unit is not playing. I would appreciate it if someone would let me know what other components down the line might need changine out.
Tim
 
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i use a 90W lamp, but up to a 150W is fine. remember it's a quick go, no-go test, that's why I have a switch across the lamp to short it out, once the lamp dims down.
far to many run continuously on the DBT which can cause the unit to malfunction because the supply voltages are straved ( low AC line = low AC secondaries) and run too low to operate properly.
 
Thanks for the helpful information. Something might be damaged on the downstream board that is keeping it from playing.
 
Sounds like you have a DC offset going and the protection is catching it. Could be a heat related drift or possibly the pots have been bumped but first pull the little preamp out to main amp in jumpers from the back to confirm the issue isn't coming from the preamp itself. I also have a 1080, been there done that and owned it for 40 years now.
 
Thanks, Arc Tech=109, for the information. I tested the speaker outputs and on the left "A" speaker got -1020 mv, on the right "A" got -1590. Then on the "B" left speaker got
-1019 mv and on the "b" right got -1592 mv. This is with the dbt on and the A and B buttons pressed appropriately. My schematic is hard to read, so could you tell me where the preamp is and how to make the connections you suggest. I haven't done work on my Pioneers in a number of years.
 
This unit worked well for me for ten years before the recent overheating from playing 4 ohm and 8 ohm speakers together. I realized that to check the preamp 20 I had to turn the receiver upside down. Who knew?
Now, on the upper board, 152, there are 3 screwed in transistors. When I took them out for replacement they had been replaced long ago by someone else who installed them with no mica insulators. Should I now put in some insulators?
 
I pulled out all the zeners and replaced them with a set I bought off ebay. The dc dropped a good bit and the 1080 has been playing well all day. I didn't add any mica shields to the transistors since no one recommended it and it seems to never have had any.

I would like for one of you knowledgable persons to let me know of a substitute for the MZ130 zener on board 152 (forward edge right behind the a1013 transistor on this 1080).
Man, I sure miss Marc.
 
steamwhistle said:
I pulled out all the zeners and replaced them with a set I bought off ebay. The dc dropped a good bit and the 1080 has been playing well all day. I didn't add any mica shields to the transistors since no one recommended it and it seems to never have had any.

I would like for one of you knowledgable persons to let me know of a substitute for the MZ130 zener on board 152 (forward edge right behind the a1013 transistor on this 1080).
Man, I sure miss Marc.
Click to expand...
 
Right. I misread the page information. The long wait time was for really large orders. Meanwhile one of the lightbulbs got smashed when I was moving the unit around on a table and the left-most glass fuse in board 152 popped. Do you know if it can be replaced by any 1.5 amp fuse? Thanks. The silence was deafening on this request so I went down to Ace hardware and bought a fuse off the rack. Put it in the 1080 and played it all day. sounds like a new 1080. Checked the dc and it was zero on both sides. The idle was 29.9. Listened to Mozart and Ernest Stoneman all day.
 
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