Quick diagnosis and repair of faulty protector circuit in sansui 881 receiver

Lights up, no sound symptom.
Check amps - ok, no offset
Check power supply - ok +- 49v
Check regulators - ok +35 and +12
Protector fault, poor dc drive to relay.
camera work was crummy. not my best work today

[@polyman2]

Please can you make sure you have your camera set up so we can see what you're measuring. Thanks.

[@tullyal]

Pity camera was not positioned correctly at the start.

[@JordanPier]

Yep. Didn't notice it had slipped after record. Pissed me off....

[@RoughJustice2k18]

Goes to show that sometimes a protection circuit can develop weird faults as well as everything else in vintage and modern electronics. Easy to overlook in some cases. Nice repair JP.

[@mrmobodies4879]

Despite the noise and camera angle which didn't bother me the explanation is excellent.

[@anthonyhfe6450]

Nice troubleshooting. My 881 has an interesting issue. It won't shut off, regardless of power switch position. So could be arc quench cap, or bad switch. Also, my 881 did not need bulbs, but has cold solder joints from the bulb's fuse clips to the board. So just remove the bulbs, resolder, and your lights won't flicker.

[@barryg41]

So what, the camera was low, everyone makes mistakes sometime. I understood what you were doing. Thanks!

[@alexkay1874]

Interesting fix thanks

[@johnyoung4039]

Sure wish I could see what you're doing on the upper screen

[@yannkitson116]

Very good with a good explanation. Shows us the cable connections to the scope please.

[@billmcdonald2436]

He was probably simply connected across the dummy loads. That’s what I do to watch the outputs.

[@justsumguy2u]

That was fun to watch, nice job. I wonder if the relay chattering like that did any pitting to the contacts?

[@pauldow1648]

Seen another tuber working on a budget disassemble the relay to assess it then clean it up and reuse it in the unit. Np.

[@tomwatkins4730]

Thank you, JP. Now I can try to diagnose my 5050 Sansui that plays (clear sound) for a few seconds then goes silent. Or, could I be looking for some resistors (PS?) that heat up and 'open up' (in

[@oldbatwit5102]

I bought a 331 in 1977, I think. I had that and a pair of crap headphones, nothing else, but I could pick up John Peel 5 nights a week and that was enough.

[@zx8401ztv]

Nice old receiver, sansui was decent. If it was mine, i would check every electrolitic and replace where needed.

[@Justplast]

My fevered :) more

[@kukko83]

I have the opposite problem to this. When I first got my Sansui 771, the relay didn't click at all. I left power on, tapped the relay a few times, and was able to get it going. The issue is, that the relay clicks in too fast. DC offset doesn't have time to stabilize, and I hear a nasty pop out of the right (wonder why not both) channel. Turning on the power, the relay clicks almost instantaneously. Right now, I just turn on the speakers some time after the relay clicks, and I'm good. I would like to get it fixed anyway, as it's not working as intended. I measured, and set the DC offset and bias to factory specs. They were both just a bit off on both channels. I shot for 0mV offset on both channels, and it kinda hovers in the 0-20mV just to take some stabs at around 50mV at max. I don't know if that's an issue of it's own or not. So, any ideas on, why the relay clicks out of protection too quickly?

[@JordanPier]

Capacitor that controls turn on timing is drying up. I wanna say it's a 220uf at 10v or something like that. I increase those to 470uf. Even when they were new they needed more time.

[@kukko83]

@@JordanPier Hey, thanks for the help! Any chance you could identify the said capacitor in the schematic for me? That is, if you have the service manual for the 771. I'm a total amateur in reading schematics but I presume it resides on the power board, and could it be either C03, ot C08? Thanks again.

[@JordanPier]

@@kukko83 c08 is your timer. Increase this one to 470uf. C07 is the fast shutoff capacitor, which if it is failing can cause the machine to go into protection randomly without any DC offset present. I'd replace both for reliability reasons

[@kukko83]

@@JordanPier Thanks again, you've been a great help! I'm a mechanical guy myself but replacing capacitors, is within my abilities.

[@kukko83]

@@JordanPier So, I went ahead, and replaced C08 with a 470uF 16V capacitor. In fact, I replaced all of the electrolytic caps on the power circuit board, excluding the bipolar ones. That's because I didn't realize they were BP when I ordered the caps. I replaced all of the other caps for ones with original values. None of this solved the original problem though. The relay still kicks in as quickly as before. Still care to offer an advice, on what to look for next?

[@mjg263]

I’ve come across so many 881’s and 771’s with a chronic background hum. Cleaning all the circuit board contacts and grounds never helped any of them, wasn’t the caps, no stray DC at the outputs, not the filter caps either. Just a low level power amp hum in the background that some people don’t care about but drives me nuts!

[@JordanPier]

Check grounds and 35v regulator. You may need a scope to check for hum on the 35v line.

[@anthonyhfe6450]

Mine's as quiet as a mouse. Never had any hum. So it was either fixed before I acquired it, or just never had this hum issue.

[@richardt1792]

That was very useful, I have a couple of receivers that stopped Clickie Clickie. You don't happen to have a shop in Southern California. If not, do you or any of your viewers know anyone that can fix these?

[@JordanPier]

I work for a shop in san diego. Classic Audio Repair.

[@richardt1792]

@@JordanPier OK, Thanks so much for the rapid response. I live in LA but I do love San Diego so I could make the drive. I have a couple of receivers that stopped working about 20 years ago. I was a single parent of twins so getting them through middle school, high school, college and 2 1/2 years in Peace Corps was my priority. Now that the kids are on their own, I am thinking about having music again. I have a Pioneer sx1980 and a Sansui 8080DB. I guess the options are fix only what is wrong or get a full overhaul, correct. Can you give me a rough idea the range in costs?

[@JordanPier]

@@richardt1792 give the store a call 11-4 weekdays and we can talk.

[@richardt1792]

@@JordanPier Ok, will do. Thanks again!

[@hestheMaster]

Electrolytic caps will fail after 20 years or so. Accurately diagnosed good fix.

[@DrCassette]

More like 40 years if the capacitors are not chemically defective (as happened with SMD capacitors in the 90s, and regular electrolytics in the 2000s).

[@mrmax1467]

Can anyone see what he’s doing or it just my screen?

[@JordanPier]

Lighting isn't great despite overhead and two spot lamps. I swear the place is a black hole.

[@johannjohann6523]

how does it work to make a "video" where no one can see anything? why bother?

[@louissparks2496]

You mispointed the camera and we can not see what you are working on. Not good.

[@pjf7943]

Tediously removing screws without a power drill..?? Testing components without showing what/where/how you are testing..????? Time to move on...

[@barryg41]

🙄

[@anthonyhfe6450]

Power drill? I never use a power drill for servicing vintage equipment. So unnecessary and clumsy. I'm with Jordan on this one.