WG 19K6100 question Q103 shorting

[komodo]

What would cause Q103 to fail with a known good game board and a rebuilt Deflection board with an LV2000 installed? I've killed three trying to figure this out with no luck. I have -32v on pin 7, -24 volts on pin 6 and 0 volts on pin 5. The positive voltages are all good. Swapped out another LV2000 with same results.

While I take a step back and look at this again, I thought I would ask here in case somebody sharp or not so sharp for that matter has some insight.

Pat

 

[komodo]

Follow up testing indicates incoming voltages from game are good and power brick as well. Pulling Q103 and testing it after it fails gives the following readings. Transistor tested good before installing it on the monitor frame. All readings are taken with a digital multimeter after it fails, Red lead is listed first.

E - C 0 volts
E - B 0 volts
B - C 1.862 volts
B - E 0 volts
C - B .476 volts
C - E 0 volts

I guess it isn't a short per se but definitely a failure of the transistor.

 

[dezbaz]

Have a read of this Pat

http://forums.arcade-museum.com/showthread.php?p=3083677

 

[komodo]

Yeah, thanks Dez. Already ruled out micas and incorrect installation. Brand new micas are put on every transistor on every monitor I rebuild. I've replaced 3 suspect sockets and triple checked my soldering and wiring. I've set this one aside for now. Started on another monitor and will come back to this in a week or so with a fresh look at it. Will post my findings once I determine what is going wrong. Who knows, it could be something very simple that I am just not seeing.

 

[Mark H]

New parts does not mean good parts...

 

[advans13]

i had an issue similar. i also went with silpad's instead of shitty micas. i prefer just to replace all of them as a group. so, 103, 606 and 706.

 

[mcandrewsoun]

If you run the deflection board with only the power supply TO-3s connected, how do the signals to the base of the output TO-3s look? I think if you have dc on the base of the transistor, it will fry it. Check for shorts in the output section (after the TO-3).

 

[dezbaz]

This is what I use to isolate a bad bank of bad transistors

 

[komodo]

New parts does not mean good parts...

I don't know. Easier to see cracks and splits in clean micas than dirty ones. I set that monitor aside for now and will take another look at it next week with fresh eyes. I will report back. I worked on another 6100 instead and got it repaired for the project I needed.

One interesting thing to note on the second monitor, I had a fully and complete working monitor but the spot killer was lit. I had never seen that before. I pored over the schematics and could not for the life of me figure out how that was possible. I then took another look at the deflection board and noticed that I had inserted Q803 backwards with no ill effects other than the spot killer being lit. Perhaps I made some silly mistake on the other monitor. It certainly wouldn't be the first time.

Thanks for the input guys. Again, will investigate and see what I find hopefully next week.