My SST's display tests perfectly in test mode and displays 99.9% of all graphics correctly. However, I've noticed that the Brain Bug stepper motor test screen and the Live Assault multi ball screen don't appear to display correctly (please see pics). Any ideas why these (2) screens would be incomplete when all others seem to appear fine? I'm not too clear on how the images are called by the CPU. Thanks! - Tim

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Update: I read that the long ribbon cable often goes bad so I did the recommended test of flipping the cable connectors (on both end of the cable). This resulted in a completely black screen. If the cable was good it shouldn't change anything since a wire is a wire. I've ordered a new cable. Hopefully that cures it.

Tried the new cable... made no difference. Hmmm....

Yep, I even checked continuity on pin 1s... to double check everything was right. I'm really at a loss on this one. I'd hate to just start replacing boards (since I don't have any spare boards for this system). The boards themselves look quite clean.

At the dot matrix display board I have -92VDC where I should have -98VDC and -113VDC where I should have -110VDC. Do you think these are outside of normal ranges? Thanks.

I've got 67.4VDC on the 68VDC pin.

Thanks Chris, as far as I can tell it only incorrectly displays these screens. I truly appreciate the guidance you provided. There is a section on the display board that looks like there's been some trauma but maybe its normal. Unfortunately this is my first and only Sega so I'm not sure what is "normal". I'm going to try replacing the display rom... maybe it got jumbled somehow. Really not sure where else to look next. thanks. df7bdb4a98c5020195c50fd5a4748b6e04f92508 (resized).jpg

Update: I got a new display rom and swapped it in. The screen did nothing... no images at all. I went back to the original rom and still nothing. I looked at the socket and it looked iffy so I replaced it. Tried it out tonight. Still no images at all. So... by messing with the board I assume something that was close to failing failed. I now need to determine if its the actual display or the control board. I would assume it's the board but I'd like to figure out a way to test the display before I spend $200+ on a new control board. Frankly, I'm in a little over my head on displays. Time to google.

I appreciate the offer Chris and I may take you up on it. One thing I noticed is that the enable display signal is not being output from the display controller board. I'll probably try tracing this back on the bench to see if I can make anything happen.

Update: I bought a new RottenDog display board since I really want to get this SST finished and trade it out. So, as of now I have replaced the display board, the two ribbon cables, and the display ROM. Once again everything works EXCEPT the Brain Bug stepper motor test screen and the Live Assault multi-ball screen! So, I'm back to where I started. Once again, the display test shows all pixels working. This points me to the MPU board?

I did the DMM test on the 74HCT273 at U201 on the CPU board (which buffers the display data) and got a few odd readings. Unfortunately that chip isn't socketed so its going to take a bit longer to swap it out and see if that's it... plus I need to order a 74HCT273. Stay tuned.

I now have a new, socketed U201 but unfortunately the display problem continues. The MPU board looks super clean.

To recap I've:
1. replaced the ribbon cable from MPU to display board
2. replaced the display board with brand new one
3. replaced ribbon cable from display board to display
4. replaced display ROM
5. replaced display buffer U201 on MPU board
6. reflowed the display connector pins on the MPU board
7. checked display voltages

This has me really stumped... does anyone have any idea what to do next?

I'd appreciate any ideas at this point.

thanks
Tim

Turns out it is the DMD. Even though everything looks good in the DMD test it must not be able to illuminate all pixels fast enough for rapidly changing text. Thank you ChrisHibler , PinballManiac40 , LTG , and Stretch7 . The help you gave is very appreciated!
Tim

The pixels look bright during the DMD test... that's so odd. I'm pretty new to DMDs.. I guess I've learned never to trust the built in test. Thanks again!

The DMD is presently mounted in the machine and there is too much reflection to get a good photo when off... here is a pic of the DMD during test mode:

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I'll take pics of the back when I swap out the DMD. I know it had a Cherry sticker on it.

I'm going to put my getaway display in it and then decide whether to get a color DMD for the getaway. That's the plan anyway.

: )

Here's a pic of the back of the old DMD. I tried it in my HS2 and it works except for displaying text that is only 1 pixel wide (see pic).

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