Electronics > Repair
BK Precision 2120 trace issues
<< < (13/36) > >>
bdunham7:
OK, very good.  Now we have a way to trace the signal through the amplifier.  We might actually be close, I've been suspecting that Q808 may be bad, but haven't had a way to prove it.  So now repeat the test on CH2/X but hook the measuring DMM to the other side of R834 (the base of Q808) and write down the voltages each way, then at the emitter of Q808 (the side with the outward pointing arrow on the schematic.

EDIT:  If you have any difficulty getting at the base or emitter of Q808, you can use the something else connected to it like R835 or R837.
vexatag:
At the base, voltage when the test load was connected was -4.37 V, voltage when the test load disconnected was 0.92 V. At the emitter, voltage when the test load was connected was -5.01 V, voltage when the test load disconnected was 0.28 V.
bdunham7:
That actually looks good--the emitter follows the base with about a 0.6 volt consistent difference.  Can you do the same tests on the base and emitter of Q807 and Q809?

EDIT:  And while we're at it, can you run the same tests measuring at the TO D1 and TO D2 terminals of the plug?

EDIT2:  Also at the junction of 835 and 836, which is the collector of Q807.
vexatag:
Here's the result of my testing

Load appliedNo loadQ807 base-8.63 V-8.63 VQ807 emitter-9.36 V-9.36 VQ809 base1.04 V1.65 VQ809 emitter0.24 V0.88 VLeft tan pin0.28 V0.91 VRight tan pin0.20 V0.65 V835/836 junction-5.37 V-2.40 V
bdunham7:
OK, we're missing something here.  Where's the power?  You had some voltage on TO D1 and TO D2 before.

Can you check the voltage at the junction of L801 and L802 (this is the+260V supply we fixed before) and then power down and measure the resistance from that junction to TO D1 and TO D2. 
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod