(Topic ID: 299603)

WMS sys 7 issue

By Theonlylilo

2 years ago



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#1 2 years ago

Hi everybody! I have a question for you.
On my Jungle Lord I have a strange issue that affects displays.
Strobes 2,4,6,8,10,12,14,16 (all displays) are brighter than the other ones. Not more, but the difference is evident.
I'm lucky ti have spare boards so the problem os located on the mpu. Where? I don't know.. changed the display PIA, the 4/16 decoder, measured with voltmeter the bus resistors and capacitors and values are all similar.. I'm stucked!
Thanks for any suggestion

#2 2 years ago

I'd probably put a scope on the outputs to measure duration of the pulse.
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#3 2 years ago

Timing issue suggests capacitors.

#4 2 years ago

There's a lot of capacitors which ones? You mean on the BCD outputs or related to a specific part? The board has been already restored by the previous owner, more chip socketed and the reset section.
FYI, if I change the 4020 with another one, the issue is strong (maybe only a coincidence)

#5 2 years ago

Hmmm probably not all bad at once I'd think. Do you have a scope to check the timing?

It didn't do it with the other MPU board? Leaves out the next culprit in the display driver board.

The only other thing that's intrusive in that circuit is this part of the timer is connected to the C line, so maybe IC7 is allowing feedback back up to the 4-16 decoder?

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#6 2 years ago

The only thing I saw with logic probe, is a little low signal on pin 2 of the timer 555. The IC is not the culprit (I bend the leg to check better).
Changed ic7 and also Q1 but nothing happens.
Other signal are pulsing like the working board.

#7 2 years ago
Quoted from Theonlylilo:

Hi everybody! I have a question for you.
On my Jungle Lord I have a strange issue that affects displays.
Strobes 2,4,6,8,10,12,14,16 (all displays) are brighter than the other ones. Not more, but the difference is evident.
I'm lucky ti have spare boards so the problem os located on the mpu. Where? I don't know.. changed the display PIA, the 4/16 decoder, measured with voltmeter the bus resistors and capacitors and values are all similar.. I'm stucked!
Thanks for any suggestion

Check for a corrupt IC 36 PIA (display comma control) which shares several signals as Display PIA

#8 2 years ago

Sorry for the delay. After checking again all signals, the culprit was IC11.
Changed and display are good again!!! Strobantastic!!!
Thanks to everybody! My eyes thank you

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