Ba2000 right channel sounds very distorted

[sansuibutch]

OK - it looks like the bias transistor isn't turning on, so it is either faulty or installed incorrectly, OR R37 (47 ohm), R39 (1K), or R41 (1K), are open or the wrong value. (also possible R29 5.6K, R31 1K). What do you have for a bias transistor? (schematic says 2SC1904) - test it, and the resistors - change anything that is out of spec (lift the resistors to be sure) - then try measuring that voltage again - you should be able to vary it a lot more.

Allright I just checked all the resistors mentioned and they are well within spec. I can't tell what bias transistors I have because the markings are on the bottom, and I know that because yesterday I pulled them and did the 6 way diode test on them. I posted the results and Overundr1 confirmed they were good. I'm at a loss. This chnnel sounded decent even with the bias problem before I shorted the left channel output. Is there any other things I should be looking at?

 

[Hyperion]

If you haven't done it already remove the left channel drivers (and pre-drivers) and test them all, I assume you have already tested the OP transistors.

Is there any chance that the bias transistor is not fitted correctly?

 

[Hyperion]

The last readings were from ground also.. hope that was what you were asking for. For these two these are the readings.

Left channel. B -1.17v
E -.507v
C -55.7v

Right channel B -1.14v
E -6.43v
C -55.7v

I thought this (bolded) should have rung alarm bells but the L channel transistor was what was changed (x2) without effect - was this a typo - did you swap the channels for these measurements by any chance?

 

[sansuibutch]

I thought this (bolded) should have rung alarm bells but the L channel transistor was what was changed (x2) without effect - was this a typo - did you swap the channels for these measurements by any chance?

Im thinking I had a decimal off on that one I just re took a few measurements and this is what I have

Tr19
E .099v
B .660v
C 55.5v
Tr20
E .647v
B 1.27v
C 55.5v
Tr21
E -.522v
B -1.136v
C -55.5v
Tr22
E -.656v
B -1.27v
C -55.5v

 

[Hyperion]

TR19 odd readings - TR23 (R55 or R59) is suspect - please take and compare readings for TR23 and TR24.

 

[sansuibutch]

TR19 odd readings - TR23 (R55 or R59) is suspect - please take and compare readings for TR23 and TR24.

Tr23
E .034v
B .089v
C 55.3v

Tr24
E .094v
B .651v
C 55.7v

 

[Hyperion]

TR23 looks dead - but check R55 and R59 first just in case.

 

[sansuibutch]

TR23 looks dead - but check R55 and R59 first just in case.

I just measured r55 and its 980 ohms. R56 is the same one in the other channel and it measures the same. I checked the colors on the resistor and they are 1kohm so there good but the schematic calls for 56ohm in them spots but I'm reluctant to believe it.
R59 and r60 are both 61 ohm resistors (both are good) but again in the schematic it calls for 220 ohms I'm there location

 

[Hyperion]

More oddities - ok, leave the resistors as they are, remove and test TR23 - let's see what we have.

 

[sansuibutch]

More oddities - ok, leave the resistors as they are, remove and test TR23 - let's see what we have.

I will pull tr23 in a few but I did notice the four resistors I circled in this pic are all 1k resistors and all read 1k in circuit except for r43 reads 63ohms. Since these are mirror circuits ,is there any significance to this? R43 is in the left channel.

 

[sansuibutch]

I will pull tr23 in a few but I did notice the four resistors I circled in this pic are all 1k resistors and all read 1k in circuit except for r43 reads 63ohms. Since these are mirror circuits ,is there any significance to this? R43 is in the left channel.

 

[Hyperion]

R43 (L) is in the protection circuit - so it may be causing some odd effect if it is 63 ohms - I presume these were not lifted to take these readings? - please lift one end of R43 to confirm, obviously replace if it is 63 ohms. Also meter probes the opposite way round when reading a component in-circuit where semiconductors are present will give different results as you are probably aware.

 

[sansuibutch]

R43 (L) is in the protection circuit - so it may be causing some odd effect if it is 63 ohms - I presume these were not lifted to take these readings? - please lift one end of R43 to confirm, obviously replace if it is 63 ohms. Also meter probes the opposite way round when reading a component in-circuit where semiconductors are present will give different results as you are probably aware.

It is definetly a 1k resistor. I did lift one end of it to confirm. Regardless of wich way I test it in circuit it reads 63 ohms. The one in the other channel in the same spot, regardless of how I measure it shows 1k ohm . I was just wondering if this shows a shorted component. Specially since the circuits are the same and the other channel don't read that way

 

[Hyperion]

Yes it might - you are exactly right to think there is something going on there.... TR15 might be shorted B-E ? D09 shorted? - do some checks - but confirm by removing/lifting one end of the component - as you have previously done.

 

[sansuibutch]

Yes it might - you are exactly right to think there is something going on there.... TR15 might be shorted B-E ? D09 shorted? - do some checks - but confirm by removing/lifting one end of the component - as you have previously done.

I think tr15 might be the issue. Across b and e it reads 60 ohms and the other 3 Read around 1k ohm between b and e. Then I removed it from the circuit and tested it and it's 60 ohms from b to e. And of course my 1k resistor that was reading 60 ohms in circuit is now reading 1 k in circuit.

 

[sansuibutch]

 

[Hyperion]

Aha ! - ok, you know what to do - replace that transistor.

What is the news of TR23 ?

 

[sansuibutch]

Aha ! - ok, you know what to do - replace that transistor.

What is the news of TR23 ?

I pulled tr23 and did the 6 way diode test and it is good. As far as the bad transistor I don't really know what any of the markings mean. What would be a good replacement? And if I'm replacing one should I replace all four on the board while I'm at it, or is that a waste of time?

 

[Hyperion]

KSC1845 - have you got any of those? - just replace the faulty one for the time being.

Not sure what to do about TR23 - if you have a replacement I would use it - I would like to say swap it with TR24 - what do you think?

 

[sansuibutch]

KSC1845 - have you got any of those? - just replace the faulty one for the time being.

Not sure what to do about TR23 - if you have a replacement I would use it - I would like to say swap it with TR24 - what do you think?

I'm going to have to order that faulty transistor anyway. The couple bucks extra for tr23 and 24 aren't gonna make a difference. If you recomend replacing them, I will. I don't want any more surprises with this amp. Even though I know setting the bias is allready gonna be a another project. I'll take it one step at a time hahah