Sansui 5000A

[cableguy2]

So I have a chance to buy a Sansui 5000A, and the owner tells me it goes into protection at about two notches up the volume scale. So I was wondering if you folks had some quick ideas at what the problem would be so I can figure on what the cost would be to do it, if you can get parts, etc. You will all very helpful when my 6060 started cracking giving me the transistors to replace in that. Very informative and helpful, saved me a lot of troubleshooting.

Thanks in advance

 

[Vehto]

I would use a Variac transformer in case something gets hot and causes further damage. see if the power transistors get warm or hot (The big ones on the heat sink)

Check the bias settings, if someone tweak those settings that would cause a problem. Download the manual.

 

[Guido57]

When I read 5000a the first thing that comes to my mind is which amplifier boards does it have. I have not seen one of these while they were failing but I have seen ones that had failed to the point where fuses blew on power up.
Leaning over the front of the unit towards the back there are two boards with two large capacitors on both sides of the pair of boards. On the top back right corner and using a flash light one can read the model of the board. If it is F-1040 or F1040-1
they may already be failing if the protection light comes on. If that is the case it may be possible to rebuild and modify them or they might need replacement with a pair of F-6013 boards. A pair of reproduction F-6013 boards is about $120, $150 if one replaces the output transistors also.
If it already has the 6013 boards then all I know how to do is check the bias and output adjustment. Note: use the 5000x service bulletin if working with 6013 boards. And DO NOT have speakers hooked up when checking the bias, recommended for the F-1040 board but not the 6013. Service manuals available via hifi engine.
there are other basics, like pulling the right/left side fuses to see if it goes into protection then.
Oh, if you haven't built a dim bulb tester when you did the 6060 it couldn't hurt to build one now.

 

[Guido57]

For the record, if you go in that deep you might just as well do a full recap.

 

[LBPete]

So I have a chance to buy a Sansui 5000A, and the owner tells me it goes into protection at about two notches up the volume scale. So I was wondering if you folks had some quick ideas at what the problem would be so I can figure on what the cost would be to do it, if you can get parts, etc. You will all very helpful when my 6060 started cracking giving me the transistors to replace in that. Very informative and helpful, saved me a lot of troubleshooting.

Thanks in advance

Better ask what he means by "goes into protection." This is a cap coupled amp, it doesn't have a protection board. As others have said verify which driver boards it has. The original boards were recalled and Sansui would replace them at no cost with updated boards well into the 1980s. If it doesn't have the newer boards, don't pay too much for it.

- Pete

 

[Guido57]

Board # F-1041 <protector> pg 28 of the service manual.
As far as my observations go I'm not sure this board (F-1041) protects very much; but there is a red light next to the tuning knob and right under the SANSUI on the front panel with a circle in the center and the word 'PROTECTOR' in an arch over the circle. It certainly doesn't protect from fried/frying F-1040 boards.
Well, technically the light isn't red. It's a plain clear bulb behind a red window on the front panel.

 

[bubhardy]

The protector board in the 5000/5000A does not disconnect the output from the speakers, because these receivers are cap coupled. It greatly reduces the output of the tone/volume control board, reducing the drive to the output stages.
In the service bulletin that details replacing the F-1040s with the F-6013s, the negative feedback circuits and the protector board disconnected and are not used. So, a properly modified 5000/5000A/5000X does not have an operating protector circuit.
There will never be any appreciable DC at the speaker outputs, unless the output caps become leaky. In a thorough rebuild/restoration, these would be replaced with modern caps, and this would take care of it.
I have successfully restored a 5000 and a 5000A, using F-6013 boards with my own layout, using leestereo’s recommendations for increasing the value/voltage of the power supply and output caps.

 

[Guido57]

It greatly reduces the output of the tone/volume control board, reducing the drive to the output stages.

Do you know what this is supposed to protect? Could this possibly save the 1040 boards if one immediately turns off the power as is recommended in the owner's manual?
There is also the possibility of modifying the F-1040 boards so they don't burn up as in their original configuration, provided one can find a unit with a working pair.

 

[bubhardy]

Do you know what this is supposed to protect? Could this possibly save the 1040 boards if one immediately turns off the power as is recommended in the owner's manual?

This is supposed to protect your driver and output transistors, by essentially cutting the signal level going to the driver boards. If I remember correctly, the problem with the F-1040 boards was the bias current going up, in an uncontrolled way, due to failure of the bias diode.
Turning off the power allows the protector SCRs to reset. If the fault still exists, when you power back up, the unit will go back into protection.
The protector circuitry in the 5000/5000A is practically useless, from everything that I've read.

There is also the possibility of modifying the F-1040 boards so they don't burn up as in their original configuration, provided one can find a unit with a working pair.

I have 2 pairs of F-1040 boards-one pair unmodified, one pair with the skippy124 mods. I couldn't get sufficient bias current with the suggested mods. That is why I did my own PCB layout of the F-6013 circuit.

 

[LBPete]

Board # F-1041 <protector> pg 28 of the service manual.
As far as my observations go I'm not sure this board (F-1041) protects very much; but there is a red light next to the tuning knob and right under the SANSUI on the front panel with a circle in the center and the word 'PROTECTOR' in an arch over the circle. It certainly doesn't protect from fried/frying F-1040 boards.
Well, technically the light isn't red. It's a plain clear bulb behind a red window on the front panel.

Sorry, I was looking at a 5000X service manual. Most X models have the F-6013 boards an do not have the protection board.

As a side note, I dug out my old well worn copy of the 5000A service manual. In it was a photocopy of a January 11, 1982 Sansui warranty bulletin #20111. This bulletin announces the end of the "Free Modification" of 3000, 3000A, 5000, 5000A and 5000X models on February 10th 1982. This end of warranty coverage is about 10 years after these units were manufactured. It also provides the parts cost, the CE-007A Kit for the 3000, 3000A is listed at $3.50 and the F-6013 Driver boards are $10 each! (That's about $31.50 in today's money)

- Pete

 

[Guido57]

The protector circuitry in the 5000/5000A is practically useless, from everything that I've read.

Agreed, unless one wants to go further and say completely useless.
Honestly, I gave up on the idea of repair/modification of the F-1040 boards as soon as I found a source for reproduction 6013s. Just know it's out there.

 

[bubhardy]

Agreed, unless one wants to go further and say completely useless.
Honestly, I gave up on the idea of repair/modification of the F-1040 boards as soon as I found a source for reproduction 6013s. Just know it's out there.

If you’re interested, you can PM me regarding my F-6013 boards.