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Sansui AU-9500 restoration issues

[QUOTE="zaibatsu, post: 13892325, member: 237942"

]We've all messed up before, a little kindness can inspire a good repair![/QUOTE

This^
 
Purchased caps and transistors from digikey, mouser and partsconnexion, nothing from eBay.

Relay clicks on and the bulb dims as it should as long as the fuses are not installed, as soon as either L or R fuse pairs are installed, the problem exists. I obviously have something(s) in backwards as others have stated.

I work a lot, but will get to checking the various suggested transistors this weekend and report my findings along with some photos of the current connections.
 
As a general observation on those new brown caps in your photos - you generally want to keep the leads as short as possible and insulate any length of component leg that remains. Those caps are just asking for the legs to either short together, or to the chassis. You need to follow the practice of how the original parts were originally factory-mounted. You want your work to be as safe (and durable over time) as how it was done in the factory.

The same goes for the resistor legs of what (I presume are) bleeder resistors across your new big caps.
 
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Good point, and yes those are bleed resistors, I believe I have output transistor issues... A pain to test and not soeso to find decent replacements.
 
Carl J72 said:
Good point, and yes those are bleed resistors, I believe I have output transistor issues... A pain to test and not soeso to find decent replacements.
Click to expand...
Easy to test - unscrew the screws - pull them and do a 6-way diode test.

Chances are if they are bung, some Onsemi replacements will do - easy to find and buy
 
Easy enough to test if transistors are shorted / dead.
You'll also want to check driver transistors as if outputs are gone the driver/s usually go with them.

At this stage you'll have two problems to resolve - the first is whatever you connected incorrectly to cause the blow up, and the blow up itself. It's worth getting familiar with diode-testing transistors, and the cheap mega328-based transistor testers (~$10) are useful to test small transistors quickly. It's also worth checking for other less-obvious blown resistors.

On a correctly functioning amp the bulb will dim (but still glow dimly) after power up, and the relay will click. Dimming with the fuses out means nothing, and usually the bulb will turn off completely. The dimly-lit part indicates that the amp is drawing bias current correctly.

I'd suggest trying to find your original mistake/s first if possible, as it'll make monitoring the results of repairing the blow-up easier.
Keeping track of every dead part # you find will help others help you later if it still doesn't come back to life.
 
So I removed and tested each of the output transistors and found 4 of 8 bad, 2 of each type. Reinstalled the remaining on the left side with fuses in and left side driver board in, bulb dims as it should and relay clicks on. I read voltage on the speaker outputs as well, but nothing across the emitter resistors.
 
You need to specify which transistors were bad (ideally with their case codes eg. 2SAxxx / 2SCxxx ) and we can recommend appropriate substitutes.
If they are 2SA679 and 2SC1079, you can use MJ15025G (PNP) and MJ15024G (NPN) from mouser.

It's good practice to remove and check the driver transistors in the event of output stage failure, as I already said.
You haven't mentioned what your original mistake was - have you found it?
 
Yes, those are the output transistors that I will have to replace. As for finding my mistakes, not totally sure, but I did notice a few questionable solder connections and broken trace on 1 connection, still looking to make sure, but the good news is that it is back up and functional on one channel. I will order replacement output transistors for the other side this evening based on the recommendations and continue the journey. Thanks again for all the help and guidance.
 
I found other threads suggesting the use of mj21193g and mj21194g as replacements for the output transistors.

ZAIBATSU - are you familiar with these?

Also wondering about suitable replacements for the 2sa483 and 2sc783, one of the output boards has a pair of shiny new looking ones which test a bit off making me think they are probably knock- offs.
 
mj21193g and mj21194g are pretty much higher-power versions of the ones that zaibatsu recommended. I'd go with his recommendation - you need to check that current/voltage seen by the MJ15025G (PNP) and MJ15024G (NPN) is within their specs, and their switching speed is also a good match.

Can you post the numbers that are printed on the subs you have for the 2sa483 and 2sc783? Onsemi MJ21193,MJ21194 could be subs for these, however Im not sure that they would be fast enough in terms of switching speed.
 
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Carl J72 said:
I found other threads suggesting the use of mj21193g and mj21194g as replacements for the output transistors.
ZAIBATSU - are you familiar with these?
Click to expand...
Yes - those are newer ring-emitter / multi-emitter type devices (i.e. LAPT in Sanken terminology) and I would use the ones I suggested over these in this particular amp, particularly if you are leaving one channel stock with the working output transistors. Both pairs will work fine, both are overkill compared to the original devices, but my suggestion is a slightly closer match to stock.

What exact readings are you seeing for the A483 C783 pair vs. the substituted pair which makes you suspect them? If the amp was working fine previously, the ECG pair may be genuine (Philips) parts someone used - I would confirm they are shorted/blown before replacing. TO-66 can be hard to replace in same package type, I'll leave it to someone else to suggest a replacement. As slimecity hints, speed is a concern for drivers.

I recommend investing in at least a cheap digital (mega328) transistor tester if you don't have one already.
 
Certainly a wise investment, lots of them on eBay and Amazon, don't mind spending a couple extra bucks on a preferred one, suggestions welcomed.

As for the bad outputs, ordered the replacements you suggested from digikey, should have them in a couple days.
 
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