Testing DMD High Voltage

I think this is a case of where the text is just a little confusing in presentation. Grounds are not all the same. Each ground connection has specific uses, and not paying attention to these requirements can cause noisy operations, system malfunctions, or even destruction of the equipment. There are essentially four types of “grounds” or “returns”: safety grounds, power returns, digital returns, and analog returns. They are making a point to use the best ground reference point for the type of circuit being measured, either the logic ground or the HV circuit ground. I'm no Gottlieb expert, but according to what I am reading in PinWiki, some measurements may be inaccurate or not show up at all if the correct ground reference is not used.

#3 9 years ago

TAK

ThatsaKicker

Inactive member

That's all very interesting! Thanks wayout.

So by your understanding, you would use the pins 4 and 5 for the black lead and pretty much ignore what it says about the grounding wires in the backbox.

Can anyone else clarify this?
I'm not going to attempt it quite yet but am nervous when I think I don't know the whole info.

#4 9 years ago

DAV

wayout440

Pinside member

Your welcome. I would use the pins 4 and 5 for the black reference lead, respective of if I was measuring for logic or HV - just when taking voltage measurements on the DMD board (Pin 4 for HV ground, Pin 5 for logic ground)

I would encourage you to take a read about some Gottlieb System 3 grounding issues here if you have not done so already: Section "1h. Getting Started: System3 Ground Issues & Fixes" http://www.beerorkid.com/pin/Gottlieb%20system%203/

1 week later

#5 9 years ago

TAK

ThatsaKicker

Inactive member

Hi guys n gals,

Thanks to wayout I successfully tested the hv as I have display issues.
I've pretty much settled that it's more than likely just at the end of life and not a hv problem but wanted to pass a few questions by yourselves.

First off my readings, under load and tested at the display itself are thus;

Pin 1 - -115.8ish (spec -112)
pin 2 - -104.4 (spec -110)
pin 6 - 4.8 (spec 5v)
pin 7 - 11.8 (spec 12v)
pin 8 - +65 (spec +62)

I believe the 5 & 12v are fine but not sure about my high, high voltage readings if someone could advise.
Google came up with peanuts.
(Haven't tested with no load yet mind)

And also my display has the symptoms described in this thread
https://pinside.com/pinball/forum/topic/outgassing-display

Where the top lines of text are missing, no matter where the text is. I've read a few threads with similar issues and while replacing the display fixes it, just got me wondering as almost always people suggest it is a driver problem
Thoughts?

Thanks for reading!.

#6 9 years ago

DAV

wayout440

Pinside member

From http://www.beerorkid.com/pin/Gottlieb%20system%203/

Are you sure you have the correct specs for the DMD? Looks to me like your -104.4 is supposed to be -100, not -110 (thus not too far off). I'm not a Gottlieb expert though.

This will allow you to connect a dot matrix display to A8P4 with a ribbon cable. Also a power cable from A8P2 (dot matrix controller) supplying +5,+12,+62,-100,-112 to the dot matrix score display is needed:

A8J2 pin 1 to DMD pin 6 (+5 volts)
A8J2 pin 2,3 to DMD pin 4,5 (ground)
A8J2 pin 4 to DMD pin 7 (+12 volts)
A8J2 pin 5 to DMD pin 8 (+62 volts)
A8J2 pin 7 to DMD pin 1 (-112 volts)
A8J2 pin 8 to DMD pin 2 (-100 volts)

I would also suggest you post a pic here of your DMD for further opinions on if it is outgassed or not.

#7 9 years ago

TAK

ThatsaKicker

Inactive member

Hey again wayout,

Bah! It is yes, sorry about that, was away from home using my phone.

Ok will take pics tonight.
In essence my high voltage section is coming up around 3-4v higher.
What's the general thoughts to how much higher/lower before it should be addressed?

Sorry if this is all obvious, cant find specific answers though.

Cheers again!

#8 9 years ago

DAV

wayout440

Pinside member

OP
Quoted from ThatsaKicker:
Hey again wayout,
Bah! It is yes, sorry about that, was away from home using my phone.
Ok will take pics tonight.
In essence my high voltage section is coming up around 3-4v higher.
What's the general thoughts to how much higher/lower before it should be addressed?
Sorry if this is all obvious, cant find specific answers though.
Cheers again!

The -100VDC is likely the "nominal" or average working cathode supply negative voltage. Most Plasma DMDs will have a maximum spec in the datasheets for the cathode supply voltage of the DMD that is more than you might think: On a nominal display requiring -100VDC for the negative voltage, the max spec is probably about -125VDC. I would assume +/- 3-4VDC off of nominal is not anything to be concerned about.

#9 9 years ago

TAK

ThatsaKicker

Inactive member