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G-9000 Driver board and Power supply board

R

redcbx78

Active Member
In the process of troubleshooting a fluctuating offset voltage (on both driver cards) I ended up smoking the left channel driver card F-2806 and a little smoke from the F-2809 Power Supply board. I can't say for sure if I was off one pin or not on the F-2806 card.

There appears to be no damage to the F-2806 card, but a nice component burn smell is coming from the R33,23,31 area.

And on the F-2806 card the R-20(maybe R-30) resistor is burnt. This is the resistor that connects the to the negative side of the C20 cap and the Emitter side of the TR10 transmitter.

Any suggestions on where to start?

I plan to lift the resistors on the 2806 card and start measuring resistance. Not for sure how to check the TR09 and TR10 transistors.

Looks like the power supply board has two individual circuits for both the right and left channels.

Any ideas on where to start on this board?

Thanks in advance.
 
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I had recapped the whole unit and the only issue I had was the offset voltage on both cards would fluctuate on either side of 0mv by a good 20mv or so. Once you started to move the volume up it would go into protection. I was suspecting an issue with the 2809 card, but never got that far.
 
Well, as I've been told, it should drift around a bit. How much a bit is, I really don't know. I fiddled with mine for quite some time then quit. Ive cranked the volume on the unit and it never went into protection. Is/was the bias on yours set at 16mV?

I was also told that it's a good idea to leave the unit on for a while to let the voltages stabalize, before making the adjustments. In this case a bit means about 15 minutes.
 
I have went through the resistors between TR09 and TR10, they all check good. Looks like resistor R33 got a little hot. So I suspect that TR09 might have been stressed. On the schematics TR09 is listeds as 2SA968?? 0,Y I have question marks as I my schematic is terrible. The component itself has the markings of T A968 y 7 k

Any body know how to check this, or the replacment part number?

Thanks again.
 
I would say you put the board in one pin out........

OR

You could have a cap like one of the 470uf caps on the driver board in backwards.....

The TR09 and TR10 are the drivers. 2SC2238 (NPN) and 2SA968 (PNP)
The substitutes for these are MJE15033 (PNP) and MJE15032 (NPN). They are common and readily available at mouser, digikey, onsemi etc etc.......

You need to check them, do a google search on AK for testing transistors to see how if you are unsure.....Remove them from circuit to test, take not where they come from, dont get them mixed up.....

I would replace all those burned resistors with metal film type. Definitely replace R17 and R20 with 1/4 watt metal film 150Ω. As it stands they are the fusible type and should be replaced regardless.....

The DC offset does drift around a bit...and especially when you make an adjustment, it will move around a bit and then settle when voltages stabilize. But there is always a small amount of movement.....
This is normal.........

Be careful plugging the driver boards in, it is very easy to get them a pin out.....
 
I know about the one pin deal, have never made that mistake before, but I guess there is a first time!

All caps on the driver board are in correctly, I have the MJE15033,and 032 in stock, so they are getting replaced. I haven't checked R17, R20 but I had replaced them during the recap, I will check them again.

So onto the power supply board!
 
R17 and R20 checked OK, I only have a multimeter but I compared TR10 to the replacement and E to B check and E to C check about the same on the old TR10 and the replacement, so I assume they are good also, but I think I will just go ahead and replace with new ones.
 
redcbx78 said:
R17 and R20 checked OK, I only have a multimeter but I compared TR10 to the replacement and E to B check and E to C check about the same on the old TR10 and the replacement, so I assume they are good also, but I think I will just go ahead and replace with new ones.
Click to expand...

You might have got away with it by the looks I would say......resistors are great at protecting things by limiting current and burning up before other components do.....

I have never put those boards in wrong either, but I have come close a couple of times.....usually spot it on the third check....it's really easy to do.

I will review the thread about the powersupply and see if I can make sense of what might have happened there....

Oh yeah, with the R17/20 they do tend to go hiZ in their old age......then suddenly they go open and presto, no bias current...
 
On the power supply board F-2809 looks like resistor R20 is burnt. An orange wire goes from there to the connector board and then into the F-2806 board. I hope that the TR10 (2SB-560) wasn't taken out. Hope R20 took the brunt.
 
R20 on F-2809 is burnt so I can't tell the resistance. Resistance is not listed on the schematic or the parts list...........uhmmmmm.
 
For some reason Sansui didnt list the values of the fusible or Non Inductance Resistors in the literature, sometimes.....other times they did.....:sigh:

I just slipped the bottom off mine and had a look.....

R20 is a 1/2watt 20Ω......just put a metal film in there....
 
redcbx78 said:
Thanks, I got my fingers crossed that is all it is!
Click to expand...

I am pretty much convinced it is, those resistors are in there also to protect the circuit....and R20 may well have done its job......
Make sure you mount it up off the circuit board so it doesnt scorch it.
 
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