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Sansui 4000 smoke got out

D

D Z

New Member
I think I discovered some old skooler's method for finding where a problem is. Unfortunately it clashed with my method and I let the smoke out of R829 on the one good amp circuit card and made it match the busted one that the 1980 shop in DC busted.

I'll rephrase. The left channel was working fine as I tested the unit I found in goodwill. I swapped the left channel card into the right channel slot and started a small fire, beginning with the destruction of R829. R815 started to brown afterward I see. Same damage on the originally broken card. I found a rigup using a NAIL in the fuse holder for the right channel. Trouble is, yeah I could replace the 100 quarter watt and the 37k quarter but they'll ignite again. I'm not adept enough with electronics to find the root cause but I've got the repair manual and a fluke 77 I've owned for 28 years.. And I'll be sad tossing the unit so if someone can help me that'd be great. One of you has gotta have a sansui 4000. Soon as I saw that honkin heatsink I knew it was worth rescuing!
 
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9 times out of 10 is that an output transistor is shorted. This was pretty much evident as the original smoked card was swapped for the other good card and it got smoked.

Sure does sound like a shorted transistor! :naughty:

Can you post any pics?
 
century tek said:
9 times out of 10 is that an output transistor is shorted. This was pretty much evident as the original smoked card was swapped for the other good card and it got smoked.

Sure does sound like a shorted transistor! :naughty:

Can you post any pics?
Click to expand...

I thought maybe the message board didn't allow pictures until I did 50 posts of "yeah that's cool" so I never even checked haha. Pictures uploaded. This 4000 still has the protective blue tape over the chrome face bezel!

You see the big heat sink at the rear of the unit.. Just wow. Underneath the pic shows most of the 0.3w resistors (in alumina? I've got fire brick made outta that from the closed steel mill) have brown heat indication i dont know thats abnormal though.
1475850519112-1953543897.jpg IMG_20161007_102716.jpg 14758511395832010655186.jpg
 
Are you near DC (since you mention it in your first post)?

I would hate to see you toss that unit; if you get to that point please let me know first as I'd be happy to set it on a shelf until I fix everything else in the queue.

But I really hope that you can repair it instead; I already have a 2000A and really enjoy it, and hope that you will similarly enjoy your 4000
 
14758549298751975812907.jpg
N8Nagel said:
Are you near DC (since you mention it in your first post)?

I would hate to see you toss that unit; if you get to that point please let me know first as I'd be happy to set it on a shelf until I fix everything else in the queue.

But I really hope that you can repair it instead; I already have a 2000A and really enjoy it, and hope that you will similarly enjoy your 4000
Click to expand...

Near sort of, yes. And passing through some. When im bored I go browse goodwill. There's a trend I'm seeing more of the 80s and some 70s era stuff showing up. I mentioned it because the DC repair shop's service sticker is on the back. Looks old. The fingernail polish covered their sticker and the same splotch covered the rim of one of the bottom panel screws. Experienced work for sure. I can't decode the repair comments on the sticker.

My fallback plan was going to be .. Well I'll consider your suggestion .. I can always buy the parts as I need. I'm endeavoring to modify existing speaker enclosures adding an internal fancooled amp to one, and shipping out boosted channel(s) to others. This transformer and sink is to drool over. There are sooo many modular circuits inside that its too tempting to just transfer the good stuff including the a b c ab ac capability and the switched filters and protector to the huge pioneer box for the ultimate computer speaker set.. Rather than use a 50w 36v diy card and have to buy everything for a expensive noisy unfeatured lower power result.

What I'm lacking is the technical skills to complete something desirable using purchased parts that may contain overkill capability and underengineered design aspects. Burning up money with essentially trial and error.. But gaining that valuable but costly "experience" I guess.

I know folks have asked 500 bucks for one of these in perfect order but I keep everything(that's fixed or not given up on) despite being broke... But yeah if you can advise me as to a path toward first-try success with my integrated speakers project so that we don't waste money(its OK to spend but not to waste) then yeah I can drop this whale off intact... Maybe swap ya for something you don't need that'll get me part way.. 14758549298751975812907.jpg
 
Oops I think I clicked reply when I was already replying.. It quoted my reply I think.. So I'll send this one too just in case its not posted..
 
I'm not your guy for a repair like that; I'm more of a mechanical guy although I did manage to successfully replace the noisy transistors in my 2000A and also replace a bad treble control in my Pilot 654 (now that's a challenging repair for space reasons) troubleshooting electronics is not my forte though.

Good news is there ARE guys here that can walk you through if you have a good multimeter and scope and can inject a signal...
 
Resistance readings on

red/yellow
1k,8k,9k,2k.

Yellow/blue
1.7k 19k 8k 2k

Red/blue
0.3 0.2 0.2 0.2(ohms)

Here's where you ask if I checked with the entire circuit intact, or with wires desoldered. They were all connected. The only ones I would have to recheck are those red/blue sets..if that's the true testing method.

Before the second card smoked, one channel actually worked. I'm gonna feel real stupid if I killed the 2 on other half of things.
 
N8Nagel said:
I'm not your guy for a repair like that; I'm more of a mechanical guy although I did manage to successfully replace the noisy transistors in my 2000A and also replace a bad treble control in my Pilot 654 (now that's a challenging repair for space reasons) troubleshooting electronics is not my forte though.

Good news is there ARE guys here that can walk you through if you have a good multimeter and scope and can inject a signal...
Click to expand...


That's cool. I'm not here for stepbystep I'm trying to use my head a bit before bothering anyone.. And I hope to simply have intelligent questions not a plea to fix my stuff.

I'll keep you in mind. I'm mechanical too.. And electronic like any parts changer can say they're electronic ;p. Back in the day however.. I did reverse code on car controllers before it was cool.
 
Not sure the sticker says anything about the nature of repairs. It looks like it may say who or when it was sealed to show any subsequent evidence of tampering.
 
D Z said:
Resistance readings on

red/yellow
1k,8k,9k,2k.

Yellow/blue
1.7k 19k 8k 2k

Red/blue
0.3 0.2 0.2 0.2(ohms)

Here's where you ask if I checked with the entire circuit intact, or with wires desoldered. They were all connected. The only ones I would have to recheck are those red/blue sets..if that's the true testing method.

Before the second card smoked, one channel actually worked. I'm gonna feel real stupid if I killed the 2 on other half of things.
Click to expand...


Oh also, I noted that only two of the four big caps charged. They ticked down from 78vdc toward zero by about a couple tenths per second(edit- after power was turned off).
 
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