Testing GO-7 B+ (and what did i blow up?)

mc300baud

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ok, since it's impossible to use "B+" as a search term and skimming GO-7 threads yielded no obvious answers...

to test the B+ on a GO-7 i know the positive lead on the meter goes on the "tubewards" leg of the large, white resistor. but where do you connect the negative lead? putting it on the a/c neutral shows a half value, but where do i check to find the actual value?

i thought i remembered someone saying you put the negative lead on the chassis (ground) so i tried that. somehow that doesn't seem to work though, as it sparked and lost the picture. both fuses are still good and i'm still getting neck glow, so what component(s) did i likely toast doing this?
 
yes, negative to the chassis frame.

go7-1.jpg
 
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Where did it spark? What part of the frame did you put the black lead on?

I personally like to use one of the little holes close to the resistor. The leads slip right in and stay there.
 
i did negative to the frame chassis on the unpainted part near the VHOLD.

and upon further inspection, it looks like it popped the larger fuse; i thought i'd checked that right after it happened (a few weeks ago) but apparently i did not. i had a pile of 3 GO-7 chassis i was working on and i guess i missed it.

so why would testing the B+ pop the fuse?
 
Did you connect the ground wire from the tube to the neckboard? Is the chassis bolted into place? All capacitor leads clipped so they don't touch the frame?
 
yes, yes, and yes. the ground wire to the cab ground was also clipped to the monitor frame.

i've got one of those Bob Roberts test circuit-breaker fuse replacements... i'll clip that in when i get a chance this week or next and see if that pops too.
 
ok, since i'm revisiting old GO-7 chassis problems...

F902 keeps blowing after i tried testing the B+ with positive to the leg of R1 and negative to the chassis frame.

what could i have shorted? Randy's flowchart mentions the diodes D901-D904; anything else i should be checking?
 
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