Amp Deflection PCB R30 fried!

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Hi;
I guess this is one of those, "did this ever happen to you" situations.
I finished up a rebuild and dialed everything in and all was good, THEN, I decided to adjust the HV shutdown on the HV PCB. I slowly dialed the HV up and then around 23kV, R30 on the deflection PCB (10ohm0.25w) resistor released it's Magic Smoke!
I quickly tested a couple close transistors and replaced it. Dialed the HV back down to where is would be about 18.5kV and fired it up, (literately) and R30 went up instantly.
Two questions remain, one is why did this happen in the first place and two, what died to cause this to happen at such a low voltage the second time I fired it up?
I'll be studying the schems tonight but was wondering,
"Did this ever happen to you?"
Thanks
Jeff
 
An observation that I had forgotten to mention was immediatly before the first fry, the spot killer LED flickered several times then POOF!
 
An observation that I had forgotten to mention was immediatly before the first fry, the spot killer LED flickered several times then POOF!
 
Good morning!
I'm pretty sure it's a green HV and green Deflection PCB set, I will verify in a bit.
Jeff
 
Good morning!
I'm pretty sure it's a green HV and green Deflection PCB set, I will verify in a bit.
Jeff

Already the problem is narrowed to the X Circuit (Because R7 did not burn too)

I think you need to start with why the Spot Killer Flickered.

Did you do the diode mods on the Deflection? If one of the diodes across Q16 and Q17 is shorted or partially shorted, this problem will occur

The shorted diode will lower the amplitude of the signal (Setting off the spot killer), and then draw a lot of current to fry the resistor
 
Dez;
Yes I did the mod, I will check it again, thanks for the suggestion and I hope you are right.
One thing, the game was working perfectly before I turned up the HV, do you think it was a coincidnece?
Jeff
 
Dez;
Yes I did the mod, I will check it again, thanks for the suggestion and I hope you are right.
One thing, the game was working perfectly before I turned up the HV, do you think it was a coincidnece?
Jeff

No, the monitor is under higher stress at 23K, so any small problem will be accentuated at higher voltage

Also, on the HV, measure R19. Should be 68K ohm. Looks like yours is misbehaving. If R19 goes higher, the HV cutoff will be lower, or unreachable
 
Dez;
I had just enough time to do a quick inspection and yes, both boards are in fact the "green" revisions.
I checked the mod on the "X" and the diode was in fact close to the trace, I must have jarred the PCB somewhere along the way to the cab...... but I did not see any arcing on the trace or the bottom of the lead of the diode but I am going to pull them anyway and insulate the leads just to be sure.
I will pull the HV PCB when I get back as well and give that a once over.
I'll update this once I get the diodes replaced and test it again.
Thanks for the moral and mental support, it is appreciated.
Jeff
 
Dez;
I had just enough time to do a quick inspection and yes, both boards are in fact the "green" revisions.
I checked the mod on the "X" and the diode was in fact close to the trace, I must have jarred the PCB somewhere along the way to the cab...... but I did not see any arcing on the trace or the bottom of the lead of the diode but I am going to pull them anyway and insulate the leads just to be sure.
I will pull the HV PCB when I get back as well and give that a once over.
I'll update this once I get the diodes replaced and test it again.
Thanks for the moral and mental support, it is appreciated.
Jeff

All the best
We will see how well "theory" holds up
 
Quick update:
I pulled the deflection and replaced the diode mod and insured total isolation of the diodes from anything else on the board.
I probed the circuit which contained R30 and found Q11 bad, replaced both Q11 and R30.
I will pull the HV PCB after I get some rest and once that has been verified, I will be firing it up, hopefully only in a figure of speech kinda way.......
Jeff
 
Quick update:
I pulled the deflection and replaced the diode mod and insured total isolation of the diodes from anything else on the board.
I probed the circuit which contained R30 and found Q11 bad, replaced both Q11 and R30.
I will pull the HV PCB after I get some rest and once that has been verified, I will be firing it up, hopefully only in a figure of speech kinda way.......
Jeff

Big relief to find something hey

All the best, them 2N3904's are dirt cheap at least
 
No, the monitor is under higher stress at 23K, so any small problem will be accentuated at higher voltage

Also, on the HV, measure R19. Should be 68K ohm. Looks like yours is misbehaving. If R19 goes higher, the HV cutoff will be lower, or unreachable

Dez;
I pulled the HV PCB and I have a question. I checked R19, (which I had replaced already) and it is a 1K ohm 0.25w resistor. I checked both revisions of the manual (1 and 2) and both list R19 as 1Kohm, am I missing something?
Thanks
Jeff
 
Last edited:
I checked the schems in both manuals I have, rev1 and rev2 and both list R19 as 1Kohm0.25w. The only difference I noticed is C3 and 4, listed in rev1 as 100uF35v and rev2 as 220uF35v.
 
OK, now I am ready to apply power to this again, (did not want to say "fire it up" anymore) and we'll see how it goes.
Jeff
 
Right- good news and bad news......

Good: No magic smoke!
Bad: Spot killer is on and a partial vertical line on the display.

I was worried that I damaged something else so I hooked up a known good deflection PCB and I got game so the problem is local to the PCB.

I will pull the schems and get busy tonight so see what I missed.

More to come...................................
 
OK, for some reason, F2 was blown. I had checked it before and it was good but of course, now it was not good......... I pulled D10 as it seemed funny but when one leg was pulled, it checked out alright.
Anyway, I replaced F2 and now got a pic, but it is shrunk in down from the top and in from the right.
I know that the game is good, (game PCB, HV PCB and CRT) as I had swapped a KGW (known good working) deflection PCB and it played great.
Now I will have to figure out what is causing this, back to the schems!

Pics attached.....

Jeff
 

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