RCA portable insuffient B+ Boost

[DaveWM]

check the HOT grid voltage and a scope if you have one. shold be around -50v and PP around 170vdc

[old_coot88]

300 ma? Holy makrel! Are you using a digital or analog meter?

[hobgoblins]

I am using a digital meter. The grip voltage is -46v and PP 145v

[DaveWM]

just to be safe, bypass the meter with a .47 cap. 300ma is way out of whack.

[DaveWM]

horz eff coil has no effect, something not right there. I prefer analog meters for looking for the dip, its a tuned circuit, so it will have a narrow range.

[ctc17]

That would be a good ring test candidate flyback. Could this be an issue with those damper diodes? or a bad effency coil? Something is WAY off for it to be that high.

[hobgoblins]

I just used an analog meter and it is also 300 ma. The current (238-250 ma) is controllable when the tv is just starting to warm up but after the HO tube gets good and hot it jumps up to 300ma and I can't turn it down.

[DaveWM]

hmmm gassey HOT. do you have another you can sub?

[DaveWM]

I can't see why it would "jump" 50+ma. I would monitor the grid voltage. Also did you check the voltages of the regulator tube?

what I like to do is get the HV prob, the scope, the vtvm, the cathode current meter and hook it all up. then start up and see whats going on.

[DaveWM]

Originally Posted by hobgoblins

I just used an analog meter and it is also 300 ma. The current (238-250 ma) is controllable when the tv is just starting to warm up but after the HO tube gets good and hot it jumps up to 300ma and I can't turn it down.

does that jump come after the HV and CRT brightness are already up?

[ctc17]

The tube will pretty much max out and red plate at 300. I bet its just thermal runaway. Its starting off to high. If C76 is leaky it can cause this.

[old_coot88]

Although the dual damper diode may check good, how hot is it running? Is it sizzling hot? (Asked previously).
oc

[hobgoblins]

Sorry about the dual damper diode. It does not get hot.

[hobgoblins]

I looked at the dual damper diode again and they do hot and they look like they are causing the high HO cathode current and the B+ boost problem also. What is the data on them. I have 1 with the code IOR D818 and 2 other ones with the code 010 7142 SCI.

[old_coot88]

Originally Posted by hobgoblins

I looked at the dual damper diode again and they do hot and..

Um.. are you saying they do run hot? If so, they are probably shot and will cause the very problem you are describing. Sorry i can't give further specs as it's been a lotta years and memory's a bit faded. I do remember that the dual diode was introduced because of the extremely high failure rate of the single. Testing the thing with an ohmeter did not reveal much, and the only real test was to sub in a new one.
oc