sys 80b board on test bench.

[hook]

i have my flaky sys 80b board on a test bench. 5.15 dc volts in.
using clays guide, i get 4.5 v at pin 40 of U1, the reset line. good
there. i get a clock signal at u1 pins 37 and 39. good there. i get a
clock signal at pins 39 of all 3 RIOT chips ( U4, U5,U6 ) good.

checking the IRQ at pin 4 of U1, its goes south. i get a square wave
for 2-3 seconds, then it goes to zero.
there is a problem there for sure. at this point, the board needs
repair, maybe the 3 riot chips, plus some others, who knows. why
would it be ok for 3 seconds, then drop out?

its not my board, so i dont want to do the repairs. who is the best
guy to send it to. the owner sent it to coinservice technology in PA.
where he started having problems. he got it back with a new battery
( there was zero acid damage) and told the board checked out OK. when
he got the board back, it was the same problem at before he sent it
out, booting up to zeros on the display, not accepting credits, no
going into test. also, at times, it wouldnt boot at all.

before i pulled the board, i did this:
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i went back to the game today and did the following. all
connections off except the PS and display connector.booted up the
board with the 3k resistor in TC1 ( i used the reset board connector
without the reset board being connected). the game booted with a slam
switch open message. so far so good. i then jumped the slam switch
( at the board) and the display went to all zeros, no strobing. at
this point i believe that it was it will do with no high scores in
memory, but i dont know that for sure. now using a jumper lead with a
diode installed , i jumped ( for a moment) the two solder pads that go
to the left coin switch and was able to add 1 credit. however, i was
not able to add any more credits. odd. i then turned off the game,
and then back on , to see if it would boot up with a credit on it. it
never booted again.

the coin door wiring and diode board for the coin door and test button
check out good.

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all this happened after it was moved from the garage to the basement.
maybe something on the playfield killed the switch matrix? how do i
ensure after the board is fixed it doesnt blow again?

thanks

[hook]

HOLD THE PHONE! i didnt have the slam jumper on when i tested on the
bench. i'll report back. sorry i missed that.

[hook]

i'm giving up. i did the slam mode, and the IRQ was good. i was going
to start checking data address lines. when i rebooted, all of a sudden
clock readings were very dirty on the scope. even the 5v had a slight
wave to it. disconnect the power from the board, and the 5v on the
scope was a nice straight line. power up the board, the 5v was
slightly wavy, the clock signal a mess, the IRQ high, with slight
waviness. this board has to be looked at by a pro.

thanks to all who tried to help

mike

[gtr...@yahoo.com]

I repair these boards.
If you are interested send me an email.

Merry Christmas
George Riley