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Sys11 entire switch collumn not working.

David_Vi

David_Vi

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5Years
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Sep 3, 2019
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Sudbury
Here's my second issue, different pin..

Got the board for DINER back. All seemed good, plugged things in one by one as Jim suggested.

Later I got around to testing switches and noticed the entire column 7 of switch matrix isn't working.
This has the jets, slings and two of the saucer switches on it.

I have continuity from the GRN VIO pin on the connector to each of the switches.
I then tried the trick jumping the header pins on the board in switch edge test. All except the GRN VIO pin activated a switch.
So one is to assume it's a board issue.

I checked the transistors, q42 being the one for that column and in a diode test it reads the same as it's brothers.

Jim tested it before he sent it back so something must have blown since I put it back together.

I have no clue what to test next. @Spandangler has tried to help up to this point but think we're now in unknown territory.
If I've blown something on the board I can just about manage swapping a component that has a few legs. Not an IC so I hope it's nothing like that. 😔

Diode test, voltage and continuity is all I can really manage on a DMM so please advise me knowing my current level.
 
you really need a logic probe to fault find any further back. if the column transistor seems ok then need a logic probe to test to see if that transistor's input (base) is being strobed correctly by the driver IC - U40 Pin12 . - at a pinch can try with a multimeter to check the voltage on the base, compare to the others - if similar voltage ok - if higher or if lower or zero then not working as it should - either bad transistor or duff U40 ic, or problem even further back to PIA U38 - with a logic probe you can find the issue in a matter of minutes.
 
AlanJ said:
you really need a logic probe to fault find any further back. if the column transistor seems ok then need a logic probe to test to see if that transistor's input (base) is being strobed correctly by the driver IC - U40 Pin12 . - at a pinch can try with a multimeter to check the voltage on the base, compare to the others - if similar voltage ok - if higher or if lower or zero then not working as it should - either bad transistor or duff U40 ic, or problem even further back to PIA U38 - with a logic probe you can find the issue in a matter of minutes.
Click to expand...

I tried that, dmm to gnd and checked the legs of U20, is that right?
They all read widely different and fluctuating so no idea what to make of that. 😔

Suppose I need a logic probe
 
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