Why are these here

[paddythegreek]

My dmd stopped working. Swapped it with a spare display and it’s fine. So why are these caps here.

 

[Paul]

Looks like they are smoothing the AC input.... However as to why they are there?? Beats me!

 

[paddythegreek]

But the values really low so like you said “why are they there”. Thanks anyway

 

[Vimtoman]

I guess they were trying to reduce noise of some sort.

 

[Moonraker]

Yep, I would say they're for noise (interference) suppression duties.

 

[strobey]

Ive also seen these on early WPC machines before, specifically remember it on a TAF.

These high voltage 10nF caps are there to suppress high frequency interference on top of the five DC voltages feeding the DMD.

I think they were likely added on by WMS during assembly.

My guess would be they started doing this around the time they implemented the shading the DMD graphics. Very early 90s. Those displays were never designed with this in mind. WMS very cleverly developed a 'strobing' technique to rapidly page between layers of graphics at different rates to give the appearance of a half tone.

I bet they had issues with early DMDs or with particular DMD manufacturers and this was a quick fix.

Pure speculation, but the timing is right and ive definitely seen this before on early games.

Tim

 

[paddythegreek]

Cheers Tim ( I pm’d you yesterday re dmd board)

 

[strobey]

Cheers Ken.. replied and paid! Maybe my email got spammed?

 

[paddythegreek]

Sorry Tim I got nothing from you in spam or any box. I pm’d you yesterday. Ken

 

[strobey]

I bet they had issues with early DMDs or with particular DMD manufacturers and this was a quick fix.

Late model Cherry DMD here and the 10nF caps are now part of the design...