Data East (TftC) DMD went black

[Schyzophrenic]

I was playing a game on my Tales from the Crypt and the DMD suddenly went completly black. There was no sign this would occur and nothing wrong with it beforehand. The machine is running fine otherwise (I can start games, play normally etc.)
I stopped playing and noticed that the fuse F7 was blown. I replaced it, turn the game on again, fuse F7 blowing immediately.
I then disconnected the DMD, replaced the fuse and restarted -> F7 Immediately blown

I checked the board (disconnected) and found some weird measurements. I then replaced the following components on the powerboard:
- C10, C11 (220uf/200V as these were the ones installed previously)
- D10 (1N4743)
- D7 and D1 by (1N4004)

The game is now starting without blowing the F7 fuse but the DMD stays black. Any idea?
I think the power board was just failing. I replaced the capacitors of the 5V circuit just a month ago as the game refused to boot!

Thank you so much for your help.

PS: I have little experience in fixing pinballs, and I got scared testing more stuff with higher voltage. I was looking for some tutorial on how to test these safely but couldn't find anything...

 

[drhex]

Resistors or Zeners die and take the transistors with them.
Good writeup here: https://www.pinwiki.com/wiki/index.php/Data_East/Sega#Testing_DMD_HV_Power

 

[Schyzophrenic]

Resistors or Zeners die and take the transistors with them.
Good writeup here: https://www.pinwiki.com/wiki/index.php/Data_East/Sega#Testing_DMD_HV_Power

Thank you. That's actually what I was reading and the line in bold made me stop
In order to test the pins, I need to remove the metal board on top (but I assume I need to keep everything plugged in?)

Also I understand I put the red probe on the pin I want to test, but where do I "clip" the black probe if my hand is on my pocket?
What kind of safety measure do I need to take so that I don't end up shocked to death?

 

[drhex]

Any ground point, e.g. the braid in the backbox. You can measure on the board, the pinoutis different on both ends iirc.

 

[Schyzophrenic]

So I finally measured the power voltage at the DMD and got the following measures:
-12
-7
No pin
0 (ground)
0 (ground)
4.9
11.7
68.7

The top two seem to be the issue according to https://www.pinwiki.com/wiki/index.php/Data_East/Sega#Testing_DMD_HV_Power

I am not sure I understand the next step though. It seems to be linked to the power board where I already replaced a bunch of parts. Not sure how to investigate this further... Any idea?
Thanks!

 

[drhex]

Yes, that is your issue. Test with DMD disconnected as well. What is unclear on the next steps? Test resistors in the negative circuit, then replace Zeners. Transistor last.