Switch matrix prob

[MartyJ]

Hi guys,

Since getting the playfield sorted from this morning, I've got another issue.

I'm getting reports of ground short on a number of switches - which is EVERYTHING in column 3 - ie left & right sling, gear shifter hi/low, top red, middle red and bottom red targets.

I've gone over each one and cannot find any issues which are obvious.  Other switches on each row (other than those in col 3) seem to be fine?

If I run the diags in test level mode - I get errors on column 8 & 3.  If I remove J207 I get no errors.

I will continue working through PinRepair's guides.  I understand U20 is often the failure on these....By removing J207 - does this isolate it to an actual prob on playfield?

Thanks


**Edit

OK, I've worked through PinRepairs guide with the alligator clip+diode for the row test on J207 other end to J209 - no errors
On the column test - alligator clip+diode for the column test on J209 other end J207 no errors other than pin 3 (switch 31)

So this would indicate possibly the U20 is gone?

[The pinballist formally known as Dean Morgan]

Dont have a schematic in front of me but if J207 is the plug leading to the playfield for these switches and when unplugged you get no error, than this proves the board is Ok and the fault is on the playfield.

[MartyJ]

Dont have a schematic in front of me but if J207 is the plug leading to the playfield for these switches and when unplugged you get no error, than this proves the board is Ok and the fault is on the playfield.

Thats what I thought too, until I did the diode / alligator clip test as per Clay's guide with the testing of columns and rows....The same column (when tested that way) without playfield attached gives shorted error....

Me thinks it the U20.  Easy enough to replace and mine looks original and is very common to go.

I found a little batt acid damage too on some resistors too....Just a little green and fuzzy, so I cleaned with tooth brush and 50/50 vinegar / water.  Letting dry under heat lamp and wont be going back in for at least a week....

[Strangeways]

Is U20 socketed ? It is a fairly common problem, as are the connectors.

But is sounds like you have isolated the problem to the board.

Why isn't it "going in for a week" ?

[MartyJ]

From reading the guides, the U20 is aparently the most common chip to go.  From looking it doesn't look to have been replaced (not socketed) but the LM339 has.  I reseated it but no luck. The machine I don't believe has had a hugely hard life so it may have slipped through.  I thought the clunking of the playfield on those damm hinges this morning I might have pinched something, but looked and looked and could see nothing.  I tested the pin 3 (connector side) on buzz to earth and nothing.  From googling it seems that the ground short error is never likely to be an actual ground short, but a 'something broke' error!  More coincidence I think.  But happy to get it out of the way now, the power board has been done, everything else clean.

The board will be out for a week as I won't be around (working up Marysville way)....

[Marty Machine]

Not sure if i missed something in the above reading, but have you tried wiggling the matrix connector while pressing the 'faulty' switches on the playfield???

Your problem might be as simple as a corroded row/col pin and not the I.C at all???

I've had this myself on a few pins now.....

MM.

[MartyJ]

Thanks MM,

Unfortunately I don't think that will help...I'm 90% sure I've isolated it to the board, without connectors plugged in.  I will replace U20, which according to PinRepairs is the most common fault with these...
I've come across some further batt damage (far right batt had let go)...I've cleaned and re-flowed what I can and buzzed out what I can.  I'll replace the U20 and see how it goes...I don't want intermittant faults, so I may look at a Rottendog replacement, if they can be sourced locally happy days!

[MartyJ]

OK U20 is out and socketed.  I'm happy with the socket and solder.  I'm still very much a novice in this area but I do enjoy it.  In the top r/h/s you can see some of the batt damage around the resistor's.  This is what concerns me.  I've scrubbed and scrubbed with tooth brush and don't think it will get much cleaner.  I know any PCB under macro 5 megapixel shots will look not good, but hmm.....

[MartyJ]

U14 out and replaced with a new socket & 74LS374.  I couldn't find any ways to test U14, so for the sake of $4.00 and about 1/2 hr better to be safe.  The guide states U14 can go depending on how the U20 died? 

[MartyJ]

U18 & U19 (LM339's) done as well.  U19 previously socketed and changed (most likely due to batt damage) but checked under socket and buzzed out ok.  Replaced LM339 and replaced U18 - socked and IC.  That should complete it.

Jumpers existing repairs.  All tested and working.  The dodgy looking resistor also buzzed out OK.  I don't like the colour of the solder on all the resisters touched by batt leakage, but I reckon the solder pads will be gone, so not worth re doing.

[Strangeways]

Good Stuff Marty !

How long did it take ? - One hour of your time !

[MartyJ]

Good Stuff Marty !

How long did it take ? - One hour of your time !

Probably about 1/2 to 3/4 hour per chip, including removal, desoldering, cleaning with isocol, new socket, solder buzz....

I used my new station to solder too.  For some reason, I didn't get as much flux (I think it is - brown stuff around solders) as I did with my old iron?  Same roll of solder too? Temp around 380deg.

I don't rush pcb's at all, I like to take my time.  Setup on the kitchen table, used my new weller PCB holder (an absolute must), bright lamp behind and slowly slowly.

Although most likely to be only the U20, whilst the board is out it was worth doing all four.  At least I'll know when I put pcb back in if it fails again to look elsewhere....

[Marty Machine]

Nice, Look at it this way "every chip re-socketed, is 1 less next time around " 

MM.

[MartyJ]

New U20 went in and no apparent switch matrix issues (will req. further testing), however direct switches now causing a few funny things....Its like the enter button is being pressed down constantly...I've checked for broken wires....The guide states generally an earth issue but not sure?

[MartyJ]

Hmm,

OK, black (earth) from switch to plug looks and buzz's out fine.

Corresponding earth pin on direct switches plug J205 buzz's out fine to earth...
U17 replaced.

No value thus far....