Hello Everybody!
I recently got a Gottlieb Dragon project and it's taken me into some board work which I'm new at (and that I was hoping for actually, for a learning experience with a cheaper pin). I've fixed a couple problems such as random game resets (I replaced the main caps) but I'm completely perplexed on 2 power readings that don't seem to be affecting the game but that I'm worried may damage something. I followed along Clay's recommendations for testing the the power and the +60v and +42v values were high by +20v each (+80 and +60) but the trim pot would not reduce the power. I figured the trim pot was dead and replaced it with a 1k ohm (this is when I replaced the 2 main caps too). Unfortunately this did not change the outcome. I triple checked that I got the right trim pot and tested (an extra one I got) separately to make sure it's actually working, which it was. I though too that maybe something is bypassing the trip pot but can't see anything that would be obvious (to my amateur eyes) that would do that. I also tried testing some of the diodes (directly on the board) to see if one is obviously faulty and could not find anything obvious again (again though, very new at this and not confident in my skills yet).
So the game actually works well, but I'm worried it might damage the displays or something else with the extra power. Also, I know the logical quick solution is to buy a new board. At this time, I'm just using this as a learning experience and I like the challenge. I've had success to far with this dog of a board (replacing parts, re-assembling the damn thing, and having it work better) so I'm not ready to give up. I'd love to hear your opinion, thanks for the help. I've attached a pic after I replaced the caps and one of the (top right) Trim Pots, and also a pic of the back.
First time asking for help here. Thanks for reading!
J

sys1-power-front-new_caps (resized).jpg

system1-power-back (resized).jpg

Oh wow, schematics! That's awesome, thanks ForceFlow !
Ya, I agree with you both, I should replace with a aftermarket board, I just get a bit determined when I try to fix something. Even if I replace it, it'll bug me if I don't figure out what the issue is here. Just crazy, ...or just sane enough to trick myself into not thinking about real life.
I've already replaced a ton of those damn molex pins. Even wrecked a pin remover already. And I've just realized I have another 10 to 20 to replace.
I still think the trim pot is being bypassed somehow. The schematics will definitely help to try to diagnose this. ...I think.
...
So Startek2 , you like Pascal boards over the rottendog and others? Have you had a bad experience with non-pascal? Or is it just something you've gone with and stuck with after?
Great info guys, thanks again.

Man, the advice keeps coming. This forum is awesome.
@ frunch :ya, someone was pretty messy with the solder. I partly learned why after finding out you need to heat this board up more than most to make it flow. I cleaned everything up between the sloppy soldering that I saw and cleaned up and flux. I can't remember if I checked the continuity on that set of pins. I'll check that next time I take it out.
KenLayton : I tested them using the negative on the c6 cap. I just check the voltages using the ground on that set of pins and I'm getting the same reading. +20v too high on both and the trim pot will not change the value either way.

...I forgot to mention, I've also done the 3 main ground mods (one on each board) just as Clay recommends. But I also tested this board before I did them and got the same readings.

foramusementonly
Hmm, the transistor, interesting. Do you have any tips or suggestions on how to test this guy?
I'm guessing just put clips on the little b-c-e tabs sticking up and use the main ground. Am I on the right track?

IMG_20190826_083105 (resized).jpg

So I tested all the Q2, Q3, and q4 first using the frame ground then realizing maybe they should be tested with the a2p3 ground.
On the
The Q2 readings on frame ground:
B 82
C 92
E 81

Q2 with a2p2 ground:
B 23
C 95
E 23

Q3:
77-82-79 (frame)
23-24-23 (a2p2)
(I'm not sure of the letters --this is from the top of the board working down)

Q4:
80 to 104 - 173 - 47 (frame)
(Keeps climbing) - 0 - 0 (a2p2)

All of these measurements don't line up with the schematics that I can tell. The Q4 seemed to have the strangest readings, but I'm not sure if what they mean. Any insights?

Now that I'm wrapping my head around the schematics and realizing this is essentially 2 boards in one, I'll go through testing everything on the lower half of the drawing and see if I can make any other assumptions. I'm getting ahead of myself too, I still need to go back through all the info @fourceflow sent me.

... Edit:
After reading Steve Corley's guide closer I went back and re-measured with the a2p3 connector unplugged. I got these measurements:
Q2:
48-98-48 (b-c-e)

Q3:
48-98-48

Q4:
(Jumps around)-40-14

I then checked the 60-42 voltages again and they are both now coming up almost 20v under now (!!-wtf). Again, the trim pot does nothing.

Thanks again everyone for your replies. I didn't really fully expect to fix this board but with your help (esp. force flow's schematics links) I actually got this repaired and surprisingly stable.
So, I couldn't diagnose what the problem was from taking dmm measurements (with the power on or off). I knew that I'd have to replace the components, so I essentially bought all the components for the 42/60 volt side. Steve Corley's schematics really helped with this (although he did make a couple mistakes, so always good to double check with originals). Just buying the components was an electronics course in itself. Before this I didn't know what a zenor diode was, that there was capacitor options, or even that resistors came in different watts. Now I understand what you can replace with what and (relatively) why. The components started to add up. I probably spent $60cdn on them all, but I also have enough extra to rebuild a few more of these if I wanted to--because many of the components came in packs of 5, that is.
I also found out that you can test the high voltage side without completely re-installing it through that damn plate (with a friend's help that has no experience with system 1s actually--although he's a natural at problem solving electronics). Saved me a ton of time. The plate is mostly a big heat sink and if you're testing only for a minute, it wouldn't (shouldn't) damage anything. But as a note, the -12 did not show up using this method (even with the Q1 soldered on--but once I properly re-installed the board, the -12 showed up again.)
So I removed most of the components, testing as I went (mostly as a learning experience, and to see who might've been right ). I still don't know for sure (I kept all the components labeled for future sleuthing) but the r12 was showing inconsistencies but I also suspect the c7, c9, c10, Q3 and q4. And it seemed like there was multiple problems, so it wouldn't surprise me if more than one of these were pooched. But it wasn't the Q2 for sure as I didn't replace this. I actually bought one, but it looked like such a challenge to replace that I opted not to after the problem was solved.
After the high voltage section was testing properly I just went ahead and did all the recommended updates to this board (except the r13, which I didn't realize until after I re-installed). Anyways, working super smooth now.
If I had this problem again though I'd just get an after market. It seams stable but there is some lifted traces and just general age that makes me feel I was a bit lucky with getting this going again. But as a learning tool, I couldn't have asked for a better teacher.
I'm mainly posting this for any future me's who found this page hoping for a solution. I hope this forum is as much help as it has been for me.
Thanks again everyone who took the time to read and reply to me. I really appreciate it.

PS: now on to the frikin' driver board. But that's another post I may open when I get stuck on it too.
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