(Topic ID: 255144)

Stern Whitestar RCT dmd blanking out. Help!

By catvilledoorman

14 days ago

Topic Stats

  • 4 posts
  • 2 Pinsiders participating
  • Latest reply 2 days ago by catvilledoorman
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Linked Games

#1 14 days ago

Hello all,
My newly purchased RCT has a progressively dying dmd. When it first arrived, it was displaying scores, etc., but the display started showing randomly blank areas that became progressively worse. Knowing little about these, I began troubleshooting as follows:
Checked all data and power cable connectors and reseated.
F Molex connectors to dmd ps were all renewed with new crimps.
Ps voltages: display connected, power on at dmd P1, pin1: -112vdc 2: -100vdc 6: 5vdc 8: 67vdc.
Swapped display into working DW, display better (higher voltages in Bally), but appears outgassed.
Ok, now the real trouble begins.
Swapped working DW dmd into RCT. On power up display now shows Stern Pinball, Coaster Tycoon, Display version a7.01, THEN GOES BLANK.
It didn't do that before I renewed the molex pins, and yes, I got them back where they belonged, triple checked before power up
Double checked display reinstalled back in DW. Ok.
Pulled driver bd Rom, checksum 02FD8DDB, Verified against downloaded Rom image, ok.
Pulled CPU Rom, cksum 00C1E5FF, verified ok.
Reseated everything with sockets.
Looked at signals from driver to dmd, (oscilloscope). Serial data runs while boot screen is on, then quits. (Flatline).
I can hear the slight squeal while the boot screen is on, quiets completely when blankout.
Dmd never lights up again until reboot.
Software problem? I definitely don't understand all that I know about that.
From the cpu at J1 on the driverboard I see reset low transit to high on start, strobe goes high, and pulses low at intervals, busy transits high for 30us at intervals, same for sat3. Stat2 and 1 no activity (low), stat0 transit high 30us. I see no activity on the data lines, only a constant approx .6vdc.

It feels like whatever program section that runs the display is not starting. I'm way out of my depth here, and cannot find any help in the big, fat stern service manual. I have no clue what the sequence of signals should be to start this thing, nor even what is controlling that sequence.

The diagnostic test buttons give bleeping sounds, but no display.

I have checked the driver for cold joints under a microscope, and didn't see anything obvious.

By the way, everything else on the machine works and plays normally. I can get guest credits, and the led display is perfect, just a black dmd.

I have been t'shooting with the outgassed board, but the results were the same when I used the good display.

Thank you in advance for any help you can give. I would consider a new display and driver, but I'm hesitant until I know where this problem lies

Rod Davis

#2 14 days ago

Don't whitestar games have a game specific eprom on the board that sits on the back of the display? Could that be your issue?

#3 14 days ago

Yes, you are right, and I verified it against the latest version of the Rom. Good checksum. Thanks!

Found Stern/Sega repair on Pinwiki. Not too much info, but today I'm following a hint about U201 on the mpu bd, a D Flip flop, it says if this buffer fails, only the "splash screen" will light on boot, then the display will go dark. That sounds like what is happening. Maybe the "Stern Pinball, etc." Screen is initialized before the real display stream starts. Keeping my fingers crossed. There is also a link to a test procedure for 74xxx chips. (Praying hands).

1 week later
#4 2 days ago

Well, boys and girls (seems like I am talking to myself here) I have isolated and cured the problem. Maybe this will help someone else in their time of need:

U201, on the MPU board was the culprit. Well, actually I was the culprit, but...

During troubleshooting I did a really dumb short cut and "hot swapped" the mpu to display controller cable (disconnected and reversed it with the power on). The point of reversing ends of the cable is to find if the problem changes, this would point to a bad cable.

Bad move. Either a static discharge or the sudden inrush of current popped U201.

Here is the way to identify the bad chip: Pins 3,4,7,8,13,14,17,18 are data going into U201, to be processed into signals to send via ribbon cable to the controller, out on pins 2,5,6,9,12,15,16,19. The 1D-8D lines were showing valid data with an oscilloscope. You could use a signal probe to see this as well. There are even threads on here that outline how to make a probe with an LED. Where I should have seen valid data out 1Q-8Q, (pins 2,5,etc..) I had a flat .5 volts. This chip was nonop.

So I replaced it with a new 74HCT273 in a double-wipe socket, and problem solved. The display is definitely outgassed, and I also found a flaky 5V line on MPU board CN2. The IDC connector had a loose wire connection, causing intermittent resets and other goofy symptoms. I replaced the IDC with a Trifurcon molex plug, and all is well in paradise.

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