Sansui 210 - Strange flash bang!

[David230]

Hi,

I was using my sansui 210 this evening and when finished turned everything off. Within a few minutes of turning the amp off there was a huge pop/crack and a flash out of the back. I was expecting to see something like an electrolytic blown or atleast something charred but I could not smell or see anything.

Seems quite strange to me but hope someone can maybe shed some light.

cheers
David

 

[petehall347]

most odd ..
did you try switching it back on ?

 

[David230]

Not yet. I wanted to have a look as I was convinced I would see something.

It was like a cap exploding. I've also checked the fuses and everything there is ok.

The 3 pots on the amp board look very black.

 

[David230]

Also when playing the amp just a little louder than usual (nothing crazy) I thought I could hear distortion that seemed in unison with the bass that smothered the whole song with a gritty distorion that was so slight I thought I might have even imagined it.

 

[David230]

Couple of pics

 

[petehall347]

nothing unusual there ..odd thing is when it is switched off it should be off . ..

 

[avionic]

Check C817 and 818 for loose connections or arcing around the solder connections. 1000µf/35vdc output coupling capacitors

 

[Tom B]

Check and see if Capacitor C008 (0.02uf @ 250v) is still intact. It is usually found mounted to the 2 legs of the power switch, or sometimes it can be found mounted to the legs of the AC Jacks in the back of the receiver.

 

[slimecity]

I'd also check that the bias settings are still within ballpark of what they should be. it would be good to know if those really blackened trimpots set the bias or not.

 

[avionic]

Check and see if Capacitor C008 (0.02uf @ 250v) is still intact. It is usually found mounted to the 2 legs of the power switch, or sometimes it can be found mounted to the legs of the AC Jacks in the back of the receiver.

That's probably a more likely culprit. It would see mains AC in either the off or on position.

 

[David230]

I have visually inspected the cap across the switch. It certainly doesn't look bad but I cant measure it until I get my other meter tomorrow. Although I could have sworn from the way it went pop alone it was a electrolytic. Its just baffling how it happened when the amp was off and for it to not be something on the input side.

The 1FD caps are solid in the pcb. Although I cant do much measuring until tomorrow when hopefully I can grab my other meter.

 

[David230]

Well nothing seemed out of the ordinary with my limited knowledge of amplifiers. So today I plugged the amp in with some spare speakers (el' cheapos) attatched and everything seemed ok. I then switched to my other speakers and had them on in the living room for the last 6 hours as a tv setup. I have just powered off the sansui and left it for over 10mins. Nothing out of the ordinary has happened, yet!

The only thing I have found is some heavy oxidation off one side of the on/off switch and surpression cap so stripped back to new clean wire and re soldered.

I would love to 100% know the cause but at the moment I am just putting it down to my sansui being like a temperamental classic sports car that likes to spit the dummy every now and then.

 

[petehall347]

do you get bad static electricity where you are ?

 

[sax6]

St Elmos ?

 

[David230]

No St Elmos

Little bit more info about the amp that is edging me towards my first refurb. (210 seems like a good intro)

I noticed it would create static charge even after it had been off the mains for a considerable amount of time. I would get a faintcrackle through the speakers when plugging them into the amp.

I also get a thud through the speakers when powering on the unit.

 

[KingBubba]

Power after switch off is due to the filter caps not having bled off all their charge. Turnoff thumps are common and usually suggests that there is no relay in this receiver. If it has one then it may be stuck in the on position. I ruined my Pioneer SA 9500II many years back by starting to poke around inside it before discharging the filter caps. My positive probe accidentally touched something wrong and I got one dead amp. It turned out that the caps needed 8-10 seconds to discharge, which I did not give them.

As far as loud noises coming from equipment, I created a noise back in the 80s that I can still hear the echo of today. In 1981 I bought a new Pioneer SX-1250. Around 1986 I brought it into work to blow out the dust on down time. Dust was a big issue back then as I lived on a dirt road and had a golden retriever. As I was cleaning it at work, the audio tech there said that while I was at it I should re-grease the outputs. He had some silicone and off I went on my first re-greasing.

A week or so later I took my receiver home, plugged it up, set up the speakers and fired it up. At the moment of ignition, foot long flames flew out of the receiver and the percussion of the blast was similar to a ten gauge shotgun shooting 3" magnum shells. I was deaf for a few seconds and then the shock took me over. I was stunned for good long while. Although not completely sure of what I did wrong, even after inspection. I came to this conclusion. When I was installing one of the outputs, one of the pins on one side did not go in the receptacle, but instead slid by and was making full contact with the aluminum of the heat shield. Where the pin had been, there was now a clean but burnt 1/2" hole in the heatsink. Back then there was no Audiokarma to help me. I had saved long and hard to buy this dream receiver and for five years, it sat on my shelf because I could not afford to have it repaired at $100/hr that the repair place charged. After staring at the damned thing for that long I could not take it anymore and I put it out with the trash and watched the trashman toss it into the truck. To this day I still get sick to my stomach thinking about that explosion. It probably led to my tinnitus.

I'm glad your receiver is still functioning and hope it stays that way

 

[David230]

Grabbed my multi with capacitance today to measure the surpessor cap and it is indeed kaput. I couldnt see it inside the insulation but there is a pin hole in the side. I was expecting to see it completely blown apart from the noise.

Where do you think I should go with this amp. I will check the elec's and resistors. I have no tuner aswell so something else to try and sort.

Any pointers as I'm new to this but have enough knowledge to perform some repairs. I would like to learn more, though.

 

[slimecity]

maybe the cap had arced from the site of the pinhole to the chassis.

Replace that cap & you should be all good?

 

[David230]

That would be my guess. I've ordered a replacement.

I would still like to get the tuner section working, but its not a massive deal just nice to have everything working.

 

[smurfer77]

Forgive me if this is known to you... that cap is a safety cap. Probably x2 class if its across the line. Note this is a legal and safety issue. It must be replaced by a safety cap.

Safety caps, when they fail are designed to fail in a certain way, electrically, and do go up with a spectacular explosion sometimes. What they don't do, is catch on fire.