BK 2040 technical help?

[KennyD]

I got the cover off it again. Testing the caps with a VTVM....

c371+ = 11.5v

c361+= 14.5v

also noticed that it looks like someone has been in here before, the brown wire that is connected to the insulated pin coming thru the box at the far right end looks like it has been broken an re-soldered. The insulators thru both boxes look broken too. Should I re-test Q312 and Q313 using an RF probe and my DMM?

I also notice that the 18v post is at just about 20v

 

[Radio Tech]

The voltages look good. The 20 volts is a bit high but I have seen this before. Since the voltage is there and not on the output transistors you should check those resistors around that location.

 

[KennyD]

the resistors around Q312 & Q313 test as follows

R400 & 401 = 10v in and 1.044v out
R397 & R398 = 11.24v in and 137.3mv out
R399 = 11.24v in and 9.9v out

397 & 398 are supposed to be 1.5k ohms but they meter out at 43-47 ohms

 

[KennyD]

Just out of curiosity, should I only be seeing 7.5 volts at the meter lights? They seem pretty dim. As far as I can tell that circuit started out from a 15v source.

Scratch that, it's the voltage drop across the light bulbs in series, it's 15 volts into the first lamp but 7.5 out.

 

[Radio Tech]

You will not be able to check those resistors in circuit. Do to other components there. That is why you are showing low ohm readings. You will have to left a leg to check them.

LED's would be nice to use. But first make sure it will not unballance another circuit. Sometimes designers use a circuit to complete another. In the case of 2 bulbs on a 15 volt circuit. 2 6 volt bulbs may have been cheaper than 2 12 volt bulbs at the time this was designed.