New forum member with a new to me G6000 that needs some help

capcapsaicin

New Member
New member to this Sansui forum and I just picked up a Sansui G6000 that needs some serious help. No sound from either the driver outputs or the headphone output. All the lights work however so that gave me some encouragement to try to get this thing working again.

Thank you to @kevzep for suggesting that start a thread on this rather than piggybacking on to this older thread http://audiokarma.org/forums/index.php?threads/new-to-forum-need-help-with-g6000.843619

I was using that thread as a guide to start my efforts in identifying the source of the problem with this receiver. I tested the output transistors according to this link https://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07 and found that both right channel transistors were bad. So I ordered 4 new ones thinking I would start fresh.

Next I went to test the driver transistors by removing the driver board from the receiver. When I took the board out I immediately heard rattling coming from the board. I am pretty sure it is coming from the caps so I assume that they are all dried out and need to be replaced. You know what happens when you assume so I thought I would check here to see if there is something I can do to verify my assumptions. Thank you for any assistance you may provide and thank you @kevzep for the assistance up to this point.

Edit: It was not the caps it was the ceramic sleeves on the C01 and C02 positions.
 
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The G-6000 is a great receiver. I have one that I used at work for 15+ years before it finally died. It has plenty of power and was a great performer for all those years. I will be getting it rehabbed, but it is third on my list behind my Sansui Eight and my Kenwood KR-8010.
 
Ok I checked the driver transistors like @kevzep suggested here http://audiokarma.org/forums/index.php?threads/new-to-forum-need-help-with-g6000.843619 and the are ok. However when I was examining the board I noticed that this resistor looked bad.


Can I test this on the board?

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Usually you can test resistors on board without removing them. If they read rated value or a little less, they are usually good. If they rate much higher than value they are bad.
 
Even though that resistor was scorched the resistance was good. 219.6Ω for a 220Ω resistor. So now I just wait on my new output transistors to arrive and all will work again!
 
I dont know whats happened there with that resistor, but thats something caused by something else, a resistor would not heat up in one spot like that and cause damage to the insulator.
What output transistors did you purchase?
 
I received my transistors and have new thermal paste to apply to the film when installing the new parts. Do I apply the thermal paste to both sides of the film?

Also, in reading about other issues with the G-6000 I read a thread about checking to make sure the relay clicks when you power the unit up. So I plugged it in and flipped the power on but the relay does not click like it should. Does this mean that the relay should be replaced or is there something before that I should check.

When inspecting the board (F-2858 Power Supply) I noticed what looks like snipped off leads at position 75 and 76. I have the service manual but I cannot find a parts list for the F-2858.

Anyone know what was supposed to be there?

F2858.jpg
 

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Yes those are wire terminals mounted and soldered from the other side of the board....
 
Since the relay does not click when I turn the power on I need to make sure it is getting power. With power on I should be getting 49v at pins 79 and 80 if I am reading the schematic correctly. Those are on the output side of the relay I believe. However I cannot tell from the schematic where to measure the input side. do I have to do that from the back side of the board?

2856-RL601.png
 
What you have ringed in red is two of the connections to the relay contacts, these carry the audio signal to the speakers if the protection circuit has not activated and the relay contacts have closed indicating normal operation. At all times these contacts should see very little DC voltage, certainly less than 0.5V and usually a lot less than 50mV (or 0.050V) if the amplifier is operating normally.

Just above your red ring you can see the circuit diagram symbol for a coil - this is where the voltage is applied to activate the relay. Normally this relay will have a transistor associated with it as it's controlling device. This transistor will act upon signals from the protection circuit to control the relay, turning the relay ON and thus closing the relay contacts and connecting the audio signal to the speakers IF there are no problems detected. But, leaving the relay in the OFF state if the protection circuit detects a problem - usually this will be 'excessive DC offset' output from one or other channel (or both).

Normally voltage is always applied to one end of the relay coil, and the switching action is accomplished by it's associated control transistor (TR609) effectively shorting the other end of the coil to ground, thus activating the relay and closing it's contacts. Note the zener diode ZD605 placed across the relay coil (to suppress transients), you should see around 28V DC (less the voltage drop across R605, 680Ω) at the cathode of this diode (right hand lead as shown in your screen shot), with respect to chassis ground. If you can see a very low voltage at the other end of this diode (w.r.t chassis) - then the relay control transistor is probably turned on - and the relay should be activated.
 
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Thank you John. I had it backwards! I'm trying to learn and I really appreciate the information! I will check this tonight.
 
I actually have 54.5v on the cathode side.
Yes, that is correct actually - I misread the schematic and thought the source was half (20Vac) of what it actually is (40Vac) - hence the correct voltage is around double. ;)

So what's happening now? - what is the power light doing? and what have you done about the 'rattling noise' you heard that you thought was ceramic capacitors?
 
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Thank you John @Hyperion

I purposefully did not replace the bad output transistors yet because I assumed that the relay was bad because it is not clicking when I turn the stereo on but the that does not seem to be the case now. I'll replace the output transistors now and see where that gets me.
 
Do you have a Dim Bulb Tester ? (DBT) - you should use one when powering up after each major component change event, or stage of restoration - especially when the components in question are the OP transistors. ;)

If the OP transistors are damaged - this will be why the relay isn't closing - because there is far too much DC voltage on the output of the amplifier.
 
Well before I read your comment I replaced all four OTs. I also deoxed all buttons and knobs. Now I have sound! Although only out of the left side. The right side is really hot. If I turn the balance all the way left it sounds great. With balance in the center the right channel is scratchy. With the balance all the way to the right that channel's volts are high and it sounds terrible. If I turn the volume up too much while the balance is on the right side the power protection kicks in and shuts down. Tone knobs, etc. do not change this sound.

I pulled the right channel OTs to make sure I didn't get thermal paste on the leads and they were clean. Not sure where to go from here. Adjust the bias?

I did find a 1974 penny and a smurfs sticker inside the case though!

I also noticed that the power supply board had a lot of the brown goo. I tried cleaning it with isopropyl alcohol but not much of it is coming off.

@Hyperion that 'rattling noise' turned out to be the ceramic sleeves on the leads of the resistors on the driver board.

20190216_202335.jpg 20190216_203322.jpg 20190216_203557.jpg
 
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OK I was able to set the output voltage at the speaker terminals to 0v for both the right and left channels by adjusting VR1, VR3, and VR2, VR4. Why does the Service Manual say to adjust both trimpots for each channel?

I was able to adjust the bias for the left channel to 4.5mv by adjusting VR5 but I am getting 23v for the right channel and adjusting VR6 has no effect at all.

I should also note that the trimpot VR5 is a replacement as it is different that all of the others on that board. I wonder if the trimpot VR6 is bad?
 

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