Ba2000 right channel sounds very distorted

[sansuibutch]

I have used a b&k 3020 sweep/function generator for years now. The one you listed would be ok as well. I like the one I use since it allows sine/square/sawtooth waveform, multi step amplitude and since the frequency set knob is continuous rotary I can do rapid sweeps checking for oscillation.
For more critical work I hook up a ST-1701a but that is another cup of tea entirely

I found one of these for a decent price. It is tested and functions as it should. I'm just not sure if it covers the frequencies I need?. GW Instek GFG-8020H.

 

[Overundr1]

That will do very nicely.

 

[sansuibutch]

That will do very nicely.

I appreciate it

 

[sansuibutch]

OK I finally received the drivers I have been waiting on for a while. I replaced the predrivers and am about to replace the four transistors that are on the heatsink on the driver board. Between the transistors and the heatsink thers a peice of plastic and it looks like it's wet with some kind of oil or somthing. I'm guessing I should just clean everything off and replace with just the plastic in between. I'm just not sure if it's some kind of compound I'm not familiar with. Does this look familiar to anybody? Thanx

 

[mroboto]

Thermal compound used by Sansui that last forever, don't know exactly what it is.

I think the best is to replace with thermal silicone pads.

Silicone is not as heat conductive as a mica with thermal thermal grease, but these transistors don't heat a lot, silicone will outlast thermal most kinds of grease.

 

[sansuibutch]

Thermal compound used by Sansui that last forever, don't know exactly what it is.

I think the best is to replace with thermal silicone pads.

Silicone is not as heat conductive as a mica with thermal thermal grease, but these transistors don't heat a lot, silicone will outlast thermal most kinds of grease.

I would agree, they don't get very warm. Thank you Mroboto

 

[sansuibutch]

Thermal compound used by Sansui that last forever, don't know exactly what it is.

I think the best is to replace with thermal silicone pads.

Silicone is not as heat conductive as a mica with thermal thermal grease, but these transistors don't heat a lot, silicone will outlast thermal most kinds of grease.

I cut some pads and punched holes in them for the drivers.. When I replaced the predrivers I noticed there was no thermal paste on them. They are mounted to independent heat sinks that stand on the board. I didn't apply any thermal paste (even though this didn't make sense) because there was definetly none on the old ones. I'm guessing the predrivers simply don't need any?

 

[sansuibutch]

Like this

 

[Overundr1]

When I did mine a while back I used a light application of thermal grease on those components.

 

[sansuibutch]

I finally put this amp back together and to no surprise the right channel is still distorted. I haven't set the bias yet and would like to try the alternative way you guys mentioned previously. Does anybody know where the test points are on the output stage to set it via MV? This pic is of all the parts replaced so far.

 

[Overundr1]

The ma measurement method post #106 works fine for this amp. Be sure to be on a dbt with at least a 100w bulb initially. Bring the right channel up to 80ma, verify the left channel at 80ma, check offset then go to mains power. Verify you are still under 100ma and wait with unit on for a minimum of ten minutes watching for bias rise (and it will if working properly).

 

[Overundr1]

If you get that far we can continue on to more specific measurements, I forget, do you have a scope?

 

[Overundr1]

You did change out the 8.2ohm resistors on the output mounting cards attached to the heatsinks yes?

 

[sansuibutch]

If you get that far we can continue on to more specific measurements, I forget, do you have a scope?

I do have a scope now. I acquired it recently and am still learning how to use it. I will set the bias the way you mentioned like I tried in the past. Fingers crossed hahahah

 

[sansuibutch]

You did change out the 8.2ohm resistors on the output mounting cards attached to the heatsinks yes?

Yes I did replace these

 

[sansuibutch]

If you get that far we can continue on to more specific measurements, I forget, do you have a scope?

OK with spinning the trimmers these are the reading I'm getting

Left channel 2.28ma - 4.21ma

Right channel 2.08ma - 3.74ma

This is obviously from counterclockwise to clockwise. I think I'm doing somthing wrong as these numbers make no sense. I have no speakers hooked up and the volume pots all the way down. That's with 100 watt bulb in the dbt Thanks

 

[sansuibutch]

Thought I messed somthing up when the negative lead of the right channel on my ddm touched the chassis but it must of popped the fuse in my ddm. Pulled out another meter and the ma readings are still the same. Wheew

 

[Overundr1]

Do you have mini grabber ends for your meter leads? If so lets take a look at bias voltages on the amplifier blocks themselves. Replace the wires and fuses.. See the two large emitter resistors on each block? Set your meter to milli-volts dc and connect one lead to the far right leg of one emitter and the other to the far left leg of the other. Write down what voltages you get and report back Also, with meter set to dc volts and one tip protected except the very tip to prevent shorts and the negative end clipped to ground measure from the outer case of each output transistor to ground. Careful here as well, much higher voltages present and a probe slip will not be a good thing.

 

[sansuibutch]

I tested those points and had absolutely no MV. I also probed the points where the blue and red wires hook to the center of those blockes. They were all 55.8 volts. Except one. It was like 46volts. But somehow while I was doing that I heard a small arc and the 100 watt bulb lit up. I don't know how because there was nothing else there to touch. I'm guessing the meter causes a little continuity and messed somthing up. Didn't smell any smoke and nothing felt hot but I have a bad feeling I smoked somthing. Now when I power on the bulb just lights up. This thing is killing me. I've tested them points in the past and this didn't happen. Damn

 

[sansuibutch]

I'm guessing I blew a output transistor. I unhooked the read wire to the left channel output and the amp turns on but the meter lights are real dim. I guess I'll try to source some output transistors and replace ..I mine as well replace them all while I'm at it.. what are good replacements for sanken 2sc1403a and 2sa745a? I've replaced over 80 components in this amp allready. What's a few more haahahaaa