Sounds like your HV's gone on your PSB........ Get a can of air, hold it upside-down and spray it on your caps...

HV meaning high voltage transformer/s? Caps meaning capacitors? You can see a blown capacitor, it will have the cooling fluid cooked out of it normaly right on top. A swelled or domed top is a sign of over heating and failing.

What you described is normal symptoms of a failing transformer. If you have blown capacitors, it could have lead to the failure, a contributing factor. Look at the PCB board, (printed circuit board). Is there any browning or discoloration, signs of overheating? It's a good place to start.

You can google the numbers on the parts to get the data sheets/values. When testing parts you should remove them from the board to get accurate readings.

I know what MCO is talking about. It's not a fix but a troubleshooting "tool". I do the same thing at work. Holding the canned air upside down will make it come out as a cold liquid. You can buy something like "Freez-It" but canned air is more readily available.

Cooling a leaking or bad capacitor will increase it's dielectric and cause contraction of the internal plates that might be shorting. We also use the same technique for troubleshooting bad IC's.

About IC's:

It's more prevalent with surface mount IC's but there are these things that grow called "tin whiskers". They have taken down some satellites when companies went to not including lead in the soldering process because of reasons you probably know. The lead slows but does not eliminate the problem. It is still not resolved and the closer and finer things get in micron spacing it's not going to get better. Spraying on a cold liquid causes these "whiskers" to contract. Many time resoldering the IC fixes the problem and it breaks the connection the "whisker" made.

Although I never owned / worked on a DE pin ,
would swapping out the power supply board with one that is known to be good
a quick way to find fault with the HV side?

Yes it would,however, DE DMD machines have 3 different generation PSB's. Only "plug n play" I know of is the aftermarkets. Of the aftermarkets 1 brand is known for killing the DMD in random machines (DON"T risk buying the cheap Rotten dog, I killed 2 DMD's on different machines w/it). K's arcade sells rebuilt PSB's for under $100 or if you have multiple DE games,do what it did.. I bought a JOLT $130 that will fit all of them. If the HV goes out I put the jolt in until I rebuild the HV on the original.

I think the solder on the dmd driver board needs to be reflowed. It is easy, only takes 30 mins or so and fixes this problem often.

Not the whole board, just the connectors and such.

but it is also possible the high voltage section does need rebuilt, however if it is working fine and then not, a reflow can fix this a lot of times.

If you need the board repaired, usually you can ship just the board to a repair shop, not the whole machine.

You have read through this, right?:

http://www.pinrepair.com/de/index3.htm#dots

From pinrepair.com:

If the dot matrix display is not working on a DataEast game, this is a summary of the things to check:

Check the voltages at the display board: -110, -98, 68, 12 and 5 volts (or within 10% of those values).

Double check the 5 volt connection to the display board.

Check the 18 volt backbox lamp matrix fuse.

Check data ribbon cable from CPU to display board.

On small 128x16 DataEast games, check/replace resistor R95 on the display.
Replace the ROMs on Display board.

More applicable:

Dot Matrix Display works for 5 minutes than goes blank.

This is a very common problem with all DataEast dot matrix displays, and is often related to the connector bring power to the display's computer board (mounted on the back dot matrix panel), or power to the display itself. On the large sized DMDs especially, the 5 volt .156" Molex connector going to the DMD's computer often needs new Trifurcon pins crimped into place (red and black wires usually). Also the 5/12/HV power going from the power supply to the display itself often develops bad .156" connectors pins too (on the display and/or the power supply), requiring new terminal pins.