Yamaha R 2000 DC offset - 79V

srinath

Super Member
This yamaha r 2000 Reads 79 v between tp1 and ground, and 79 v between tp2 and ground, and 0 between 1 and 2 in the front power amp section.

The heat sink attached to the voltage amp chip also got very very warm in a few mins.

Would someone be able to tell me what could be the problem.

The manual - I am going to look @ it, but I get more practical knowlwdge from you guys here.
Thanks millions in advance.

Cool.
Srinath.
 
It sounds like shorted output transistor(s). Power off, measure for shorts on the output transistors.
 
BCE's

OK, let me refresh my electronics here. They are B,C and E
Base, collector and emitter.

The base is ground, collector and emitter will not have continuity to ground if its good right. The one that is shorting to ground = toast ? what else is it going to tell me.

BTW manual totally skips this.

Cool.
Srinath.
 
OK I will yank that section out tommorow with the heat sink and test em. The correct resistance value is ? or what would be low ? 0 = short I know that.
Thanks.
Cool.
Srinath.
 
Check with www.bdent.com, they sold me subs for an R-2000 that I restored, and that voltage amplifier STK runs hot you need to add extrra heatsink to the one it already has. There is ample room above the chip to screw on more heatsink.
 
Pull out the power transistors on the bad channel, and check for shorted driver transistors (2SA968 and 2SC2238).
 
Yes sir.

Check with www.bdent.com, they sold me subs for an R-2000 that I restored, and that voltage amplifier STK runs hot you need to add extrra heatsink to the one it already has. There is ample room above the chip to screw on more heatsink.

I have read your posts on that topic. It will be heat sunked.
Thanks for the bdent link. I'll get on it and check it.

BrocLuno: I hope I get it working too.
ecluser: oh OK you say its not the 2 power transistors 2sa1170 and the 2sa2774 ? See the collector seems to flash short to ground. Like it says open, and 3-4 sec later it says 12 ohm (just a random number) then back to open. That is with it not powered up. Does that still mean the problem is elsewhere ? I'll definetly look though, learning is what I spend the big $ on this amp for ... all 10 bucks of it are all for learning.

Cool.
Srinath.
 
I didn't mean the 2sa1170 and the 2sC2774 are good. I meant that if the power transistors are bad, there is chance that the driver transistors are bad too. You must check all the components in this area.

TP2 (ref to post #4) is not the ground, it is the output. How did you test the power transistors exactly?
 
This 1 sec.

Check for low resistance between the collector (C) and TP2, for each power transistor.


OK on both sets being dead. MCM electronics has the driver transistors for 1.39 and the 1 2sa1170 I believe also for 1.39. I may just buy and replace em.

Collector is the center pin on the power transistors 2sa1170 and the 2sC2774.

I will check those to TP2 but what do I test it for - resistance/short ? voltage with it plugged in ?

I checked the collector pins to ground on both power transistors and got the intermittent resistance flashy thing.

Thanks ecluser.
Cool.
Srinath.
 
I checked the collector pins to ground on both power transistors and got the intermittent resistance flashy thing.

When you do this, you actually measure the resistance of the main filter caps because one side of the cap is connected to the collector of the power transistor, and the other side of the cap is connected to ground.

It is not easy (and automatic) to test a power transistor in the circuit because the junctions are more or less shunted by the other components in the circuit.

But we are looking here for a short between the collector and emitter, for this test you can measure the resistance (low Ohm scale) directly between the collector and emitter, in the circuit, with power OFF. Anything less than 100 Ohms is suspicious.
 
Collector to emitter on that side's power transistors stay open and flashes to a lowish value every few seconds.

I'll print this thread out and refer to it as checking.

Cool.
Srinath.
 
Its alive ... sorta.

I pulled the bad board out and its working on the other channel.

I'd put the good board in the location of the bad board and make sure the thing still works.

Then I'll yank the components off the bad board and test em 1 by 1.
Thanks guys.
Cool.
Srinath.
 
Did you remove the power drive sub assembly only?

If only the "power drive" section is removed, you can test the rest of your circuit (the STK voltage amp) if you connect a resistor from the cathode of D411 to the output point TP2, and another resistor from the anode of D413 to TP2. Both resistor must have the same value but this value is not critical, something like 200 Ohms will be perfect. If this side of the STK is good, you should have a very low offset at TP2. But if you have a large offset at TP2 with the "power drive" section removed, the "power drive" section is probably good.
 
I removed the board ... the one that has the 2 power transistors, the 2 drive transistors and a bunch of caps and resistors and diodes. but its a small board connected to the heat sink.
Oh OK that I will read again and see if I can do that.
However I was going to do this - swap the 2 wire plug - I am guessing from the preamp board ... so the right output gets its input from the left side preamp.
Then I was going to move the whole power amp section board to the front part of the heat sink ... so the thing will now be connected to the left side of the ouput side of the spatial expander. If I test that way, I'd then know its got everything else working fine.
Your method will let me run the amp aithout blowing up something if something else is wrong.
Cool.
Srinath.
 
OK I did a few unscientific things.
The bad circuit was the left one and the power/driver board for it was the one closer to the front of the amp.
I pulled that out yesterday.
Today I put it in but in the rear location and connected it to the right circuit.
I also put the board form the rear in the front. So basically I swapped the power amp section left to right.
That resulted in no sound and no safety relay clicking.
I knew that ... a high DC board should not trip the relay whether its left or right. Then I unplugged the bad board, which now is the rear board. Safety relay clicks. Sadly though, no sound. Then I pulled the front board off and put it in the rear. Sound out the right only.
So the left circuit has a bad power amp board where all the power and drive transistors live. It also has a bad something or other before getting to that point.

Time to run your experiment now I guess Ecluser.

Any one have some more ideas ? I am grateful for all the great tips I have been getting. Excellent guys and gals, thanks.

Oh, the spatial expander in the thing just produces static. It has to be off. Its dead.

Cool.
Srinath.
 
I thought that too. Could I pull it and flip it around to make sure that that problem now flips to the other channel ?
Can somethign else be the issue as well, no sense frying a chip and other stuff ?

Which is the input in that board, there is the 2 pin wire pigtail that is not related to the output. Swapping it made no diff
The 6 pin plug has input and output ? I want to tap into that in the bad channel once I find out what it is, so I know its got the signal.
Thanks a million.
Cool.
Srinath.
 
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