Re: DC503 Not Working

Harvey White

Once you get the extender, check the strobes on each of the digits.  Then check the source of those strobes.  Then check the chip that's driving those (likely) transistors.  A typical way is to have a counter driving a decoder which then drives the digits individually.  You may find that this counter does all of that in one chip.  If it's a complicated chip, then look for a reason (if no strobes) that the chip is being inhibited.

Anything where digits freeze or are irregularly displayed indicates the scanning electronics.  Anything where there's a missing segment on ALL displays indicates the common 7447 decoder or the like.  Anything where you have one segment on one display missing tends to indicate a problem on that display.

Even if the display is wonky, you might see (and perhaps should see) digits indicating counting.  The counter is very sensitive to the input settings even on a good day.

You're going to need the JAMMA extender.  My research suggests that if you have all the lower pins connected on both sides, equivalent to 1 to 13 when you turn the extender upside down, all you need to do is mark both connectors promently, and reverse the connectors.  On the JAMMA connectors I saw, pin 7 was missing on both sides.  No other pins were missing, which suggests the reversal.

I wouldn't do much more until you can get that counter out on an extender.  Make the extension wires long enough to get the plugin at least one plugin length away from the front of the frame.


On 8/4/2020 5:59 PM, Stephen wrote:
I got to working on bit on this unit today again. I rechecked all the voltages, and they’re all good.
For good measure, I replaced all the tantalums on the lower board. 2 with electrolytics, the 15uF/50V and the 6.8uF, which I couldn’t find. And of course nothing has changed, I yet have to find time to modify the JAMMA extender. After all that has been changed, there is close to no improvement...

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