Sansui 3000A with factory suggested mod has channel out....HELP PLEASE!

[oconnorweb]

Hey all. Picked up a Sansui 3000A in good cosmetic shape to add to the collection. Had read mixed reviews on this unit and how it has issues. Still brought it home. Have a hard time saying no to vintage Sansui.

Anyway when I tested it pre-purchase with headphones (my first mistake) I got sound out of both channels but it was as expected dirty. I thought some deoxit on the balance and volume pots would do the trick.

Got it home and did the necessary cleaning. Headphones ...again...and still the dirty sound out of the left. Realized then then the left was also tinny and much weaker. Right was fine.

Got some speakers hooked up and no sound out of left. Right fine.

Open up the bottom to find that the 2 fuses for the left were blown. Great!!! Maybe I can replace the fuses and get this receiver up and running.

Replaced all the fuses and started it up and blew the 2 left fuses again. Ouch.

I'm hoping I can get this unit working. I have limited experience in recapping.

I do see that's it's been modified as recommended by Sansui so that it doesn't blow woofers and burn down the house.

This thread shows a pic with the original configuration:

http://www.audiokarma.org/forums/showthread.php?t=373457

Below is a pic or two of my unit with the necessary mod. Correct?

OK. What is my next step? I do not see anything burned out. I can take another pic of a certain area if that may help.

I know this is not some prized purchase. I'm running a 9090db right now that I will never part with it. I just have a weird feeling that I have to get this thing running. Maybe a Christmas gift for my brother in law that needs to get back into vintage/vinyl.

Any detailed help is much appreciated.

Cheers

 

[tom3]

Three things come to mind right off, although it could be lots of things. Shorted/bad output transistor, same with the drivers in the heat sinks, or a bad diode in the driver amp. Got some work ahead of you, pretty easy amp to work on anyway.

 

[Sam Cogley]

Check what Tom said first.

If those are the capacitors for the output mod, they're certainly not the factory recommended parts or installation method...so they might not have changed out the diodes on the driver board that need to go. The factory kit used radial caps in a pair of clamps on a shield under there. My 3000A didn't have it so I hot glued the caps in place. Where are those caps connected? They almost look more like some sort of weird modification to the power supply.

 

[dr*audio]

Most likely blown output transistors on the left channel. The bias pots can open up, causing the output transistors to blow. You are so lucky to have found one with a wood cabinet! IMO, the 3000A is a far better receiver than the 9090dB. When you get it repaired you will see. Better tuner, better sound, separate power supplies for each channel. There is a guy here who is designing a replacement board for the 3000A, to make it more stable and retain the original sound. It is almost done.
Contact member tgarson for info about the upgrade kit.

 

[oconnorweb]

Thanks for the replies. I took some close up pics of the mod done on this unit. It does have a sticker on the bottom of a service shop.

The brown cap is 1000 mfd 50. Looks like same specs as service bulletin suggested? Also looks to be bad as stuff oozed out of top, right? Do you think this is the root of my left channel being out?

Should I start by replacing these two caps, the brown and black?

I know the service bulletin included changing out some resistors and diodes. Cant't tell yet if that's been done.

Thanks for your thoughts......

 

[dr*audio]

It looks to me like the cap with the black electrical tape around it is a replacement for a brown cap. It is possible the remaining brown cap is shorted but it is more likely a bias pot opened up.

 

[Sam Cogley]

If you're handy with a soldering iron, order the right diodes and change them out. Diodes are cheap, and then you'll know the right parts are in there. Change out those caps, too - they're old. Not saying that either one will fix your problem, but they're good preventative maintenance.

 

[oconnorweb]

Thanks again.

I did some general cleaning of the 3000A and it really is in good/great shape. The wood cabinet is sweet.

I spent some time looking at the service manual and the service bulletin (attached).

Here's what I figured out. Who ever did the mod stopped at the caps. Look at the pics of the resistor. It's got the original specs of 3w. Guessing the diodes are original as well.

The SB calls for 2 1000 uf 35 wv non polar electrolytic caps. My mod has 2 different caps. One is 1000uf; the other I'm not sure as no markings. Probably what ever the shop owner had laying around?

I'm gonna order the parts listed in the SB and see if that cures my lost channel.

I'm not that familiar with the specs of these parts so pls bear with me and give me a hand if you would. I only want to order these once if I can:

Two 1000uf 35 wv caps


http://www.digikey.com.au/product-detail/en/RFS-35V102MK8#5/604-1069-ND/970230

or

http://www.mouser.com/ProductDetail...GAEpiMZZMtZ1n0r9vR22YT02h/38WmxEOhpZ4Us6%2bA=

Four 1 ohm 3w resistors

http://www.digikey.com.au/product-detail/en/ERX-3SJ1R0/P1.0W-3BK-ND/36521

Eight diodes S 1.5 - 02

I'm lost here. I see no corresponding specs on Digikey or Mouser

I really appreciate any help on this. I'd like to get my order in and hopefully bring this unit back to life.

Oh and the SB calls for new fuses 2A but no mention of voltage. Thoughts?

Cheers

 

[Sam Cogley]

1N4002 will work just fine for the diodes.

 

[dr*audio]

Thanks again.

I did some general cleaning of the 3000A and it really is in good/great shape. The wood cabinet is sweet.

I spent some time looking at the service manual and the service bulletin (attached).

Here's what I figured out. Who ever did the mod stopped at the caps. Look at the pics of the resistor. It's got the original specs of 3w. Guessing the diodes are original as well.

The SB calls for 2 1000 uf 35 wv non polar electrolytic caps. My mod has 2 different caps. One is 1000uf; the other I'm not sure as no markings. Probably what ever the shop owner had laying around?

I'm gonna order the parts listed in the SB and see if that cures my lost channel.

I'm not that familiar with the specs of these parts so pls bear with me and give me a hand if you would. I only want to order these once if I can:

Two 1000uf 35 wv caps


http://www.digikey.com.au/product-detail/en/RFS-35V102MK8#5/604-1069-ND/970230

or

http://www.mouser.com/ProductDetail...GAEpiMZZMtZ1n0r9vR22YT02h/38WmxEOhpZ4Us6%2bA=

Four 1 ohm 3w resistors

http://www.digikey.com.au/product-detail/en/ERX-3SJ1R0/P1.0W-3BK-ND/36521

Eight diodes S 1.5 - 02

I'm lost here. I see no corresponding specs on Digikey or Mouser

I really appreciate any help on this. I'd like to get my order in and hopefully bring this unit back to life.

Oh and the SB calls for new fuses 2A but no mention of voltage. Thoughts?

Cheers

You need to check the output transistors. The mod will not fix this problem. There is a short that is blowing the fuse. Even if those caps were shorted it would not blow the fuse with no speaker connected. Search on AK for "How to test transistors."

 

[oconnorweb]

That raises a point dr audio.

I'm pretty sure the speakers were hooked up and the selector on for the speakers when I installed the new fuses and the 2 left ones blew again.

What if I unhook the speakers, turn the speaker selector to none, replace the fuses and see what happens when I turn on the unit and play a source.

If the fuses do not blow does that suggest its likely the blown mod cap rather than an output transistor? :scratch2:

thanks gents

 

[kevzep]

That raises a point dr audio.

I'm pretty sure the speakers were hooked up and the selector on for the speakers when I installed the new fuses and the 2 left ones blew again.

What if I unhook the speakers, turn the speaker selector to none, replace the fuses and see what happens when I turn on the unit and play a source.

If the fuses do not blow does that suggest its likely the blown mod cap rather than an output transistor? :scratch2:

thanks gents

Can I just say, every time you power it up and blow a fuse, you could actually be doing more damage to the amplifier....Yes the fuses blow to protect the circuit, but fuses are no match for how quickly things can go bad in semi-conductors.......

You need to pull the output transistors and test them.
Pretty much the only thing that will take the fuses out like that is a shorted transistor....

I would also pull the driver transistors and test them too......

I can almost guarantee you will find the transistors have shorted.....

So put the shoddy work right, test transistors, and asses where you are after that....

 

[dr*audio]

Can I just say, every time you power it up and blow a fuse, you could actually be doing more damage to the amplifier....Yes the fuses blow to protect the circuit, but fuses are no match for how quickly things can go bad in semi-conductors.......

You need to pull the output transistors and test them.
Pretty much the only thing that will take the fuses out like that is a shorted transistor....

I would also pull the driver transistors and test them too......

I can almost guarantee you will find the transistors have shorted.....

So put the shoddy work right, test transistors, and asses where you are after that....

Thank you, Kev.

 

[DCinDC]

Dim Bulb Tester... It costs less to make than a box of 5 fuses.

yeah that old Mallory brown cap spooged.

I would recommend up-sizing those output caps to 2000uf at least. And I don't think it has to be non polarized cap either. Lots of cap coupled amps had polarized output caps. Including Sansui's.

 

[skippy124]

I would recommend up-sizing those output caps to 2000uf at least. And I don't think it has to be non polarized cap either. Lots of cap coupled amps had polarized output caps. Including Sansui's.

Re the polarized vs non-polarized, IIRC most, if not all, cap coupled amps have a single voltage rail, so the output of the amp before the cap is always positive (or negative depending on the particular design) with respect to ground, hence a polarized cap can be used. In this particular case, the amp topology is +/-voltage rails, and hence the output can swing from positive to negative with respect to ground, and a non polarized cap is required.


Cheers

John

 

[oconnorweb]

I'll order the shorted resistors while I'm at it.

Alright I'm not that experienced with this so bear with me pls....

Output transistors are located on pre-power board TRD-2C parts # TR801 - TR804?

Driver transistors are located on the driver amp board TRD-6B parts # TR805 - TR808?

Testing the transistors.... Is there an inexpensive tool I can purchase to do this task?

I realize I'm a nubie and probably earning some well deserved chuckles and even a groan or two but I do share the love for analog vintage stereo equipment.

Thanks for your patience.... :thmbsp:

 

[DCinDC]

Re the polarized vs non-polarized, IIRC most, if not all, cap coupled amps have a single voltage rail, so the output of the amp before the cap is always positive (or negative depending on the particular design) with respect to ground, hence a polarized cap can be used. In this particular case, the amp topology is +/-voltage rails, and hence the output can swing from positive to negative with respect to ground, and a non polarized cap is required.

ahhhh! Thank you Sir

 

[tom3]

Outputs (4) are on the back panel under the formed screen panel with the Sansui logo on it. Two screws in each. Watch for the thin glass looking mica insulators under the transistors, important items there. Make note which socket each comes out of. Drivers on amp board TRD-6B are not powered by the fused circuit, I wouldn't suspect them at this point. This amp has the predrivers (6B), transformers, drivers (2D), outputs.

 

[oconnorweb]

tom3 I do not see where the outputs are; first are they transistors? Are they on a board?

I see do transistors...4 ... on the pre-power board TRD-2C...pics below.

 

[oconnorweb]

forgot the pic.....