Data East Power supply - 520-5047-02

Tyrone Powers

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Question for the Experts.

Picked up a data east Rocky and Bullwinkle with a non-working display. Initial Power up had working GI, sound and flippers but no display. After replacing fuses in the power supply and checking connections, upon power up R17 (which feeds to the -98V on the DMD board) burned up....literally. Other than it possibly having been a 1/4W versus the required 1/2 W - any ideas as to why? Once R17 blew I discovered that the 0.5A Fuse connector for F7 was fractured. Other than taking 90V to ground I can't see what this connection does from the schematic.

I can do board repair, but I have a feeling that this might be chasing down a rabbit hole that might be better served just getting a new PS board.

Curious what the community thinks. Thanks!
 
OK, digging deeper I found what appears to be a faulty Zener diode in the same circuit (-98V circuit.) The diode, unpowered is reading as a short across the leads.

Anyone else seen this on this power supply? As I dig I'll keep posting so other might learn from my trial and error. Pinwiki does touch on this diode as well so I feel like I might be on the right track.
 
So, the power supply saga continues. The back of the circuit board presented with the "bubbles" you see in the picture. Additionally the board mask if starting to bubble and peel as well. Has anyone seen this before? Symptom of too much load for too long?
 

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A shorted diode can certainly cause very bad (and dramatic) failures in my experience; sounds like you're on the right track.

As for the masking on the back - looks pretty normal to me; big traces, lots of solder - masking looks normal in my opinion...
 
So, the power supply saga continues. The back of the circuit board presented with the "bubbles" you see in the picture. Additionally the board mask if starting to bubble and peel as well. Has anyone seen this before? Symptom of too much load for too long?

These bubbles and peeling solder mask won't hurt anything. This is common with older boads and is due to how the board was fabricated. After etching - the bare boards are tin-lead plated and then the green mask is applied. When these boards are ran through the wave solder machine, the plating melts underneath the solder mask creating what you see.
This fabrication process is seldom used anymore. Most people (including me) prefer to have the boards fabricated as SMOBC or solder mask over bare copper (no plating underneath the soldermask).

Ed
 
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