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Trol

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This one had letters all over the screen and a garbled wizard that only was on the very bottom of the screen.
Started with my usual habit of shorting ic pins and flexing the board.

When shorting pins on the 2114 rams@ ic9, 10 and 11 on the bottom board, I noticed the letters all over the screen changed.
Decided to unsolder all three and put sockets in to test wich ones were bad. After replacing ic 10, the letters were gone and I had a clean screen.

Had a few beers to celebrate and, the letters were back, but different..... Replacing ic 11 did the trick, glad I socketed all three rams:)

Now I still had the garbled wizard who loved to be at the bottom of the screen and nowhere else.
Decided to shotgun all of the 14 and 16 pin ttl chips with my logic comparator.
While shotgunning, I noticed that the wizard sprite cleans up when I press the 5808 ram between ic 86 and ic 89. Replaced the socket, and we have a clean wizard sprite.

All of the ttls I could test with my comparator checked out ok, except for the ls 161 and 163 chips, which are counters so probably cannot be tested with a logic comparator
I put my comparator in logic clip mode with the universal zif card to check activity on the pins of the 161 and 163 chips.
The 161 chips checked out doing more or less the same on every pin,but the 163@ ic100 was dead on all outputs.
Replacing it, got the wizard back where he should be.
 
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Mitsurugi-w

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Nice. I have a logic comparator also. Would love a video showing how to use it to troubleshoot arcade games. :)
 

Trol

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You don't need a video, it's easy.
Do you have the HP, with some cards?
 

caius

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Checking counters with a logic comparator gives false positives most of times, this is due high speed propagation time of such devices.
 

Mitsurugi-w

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Yes I have the HP. NOS unit.
 

Trol

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Just plug a reference card in the comparator, say 74ls00 and find a 74ls00 on your board and put the clip on te chip.
Take notice of the "pin 1" mark on the clip. 14 or 16 pin chips, pin1 needs to be on pin 1 of the chip.

Power on the game, if the chip is ok, you'll only see the "on" led lighting, if any other led is lighting, something is wrong.
What happens a lot here is that the clip doesn't make good contact with the chip on the board and it gives false readings, so make sure the chip legs are clean or wiggle the clip a bit before you power on the board.

If you are lucky enough to have the universal zif card: insert a good working chip in thezif socket.
Look up the datasheet for the chip you want to test, look at the output pins. The dip switches of the output pins should be put outwards, to the edge of the pcb.
the switch should be to the left, as you look at it while holding the comparator.

If you want to use the zif card and comparator as a logic clip, put the switch to the right and all the dip switches outwards: left bank to the left and right bank to the right.

All it does, is comparing the outputs of the chip inserted in the comparator to the chip you put the clip on.
 
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Trol

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Are there chips soldered on your test cards ?

If not, solder a known working ic into the card, bend over gnd and vcc to the appropriate lines and make sure the output lines of the ic don't connect to the edge.(drill the via's or cut the traces).
 
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stj

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i also have the HP,
there was a guy somewhere who made a universal card for it using a pld and a number of rotary switches to dial up the ic number.
i dont know how well that worked or if he sold them.
 

Trol

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Douglasgb on KLOV has some blank universal cards.
But there is some work: the shape of the pcb is flipped, so you have to grind down one side of the pcb to make it fit in the comparator, and there is copper between the contacts which you have to peel off.
Other than that, it's working fine.

He also sells reference cards, old style where you have to drill the output via's like original, and new style where you have solderpads to bridge all the pins except the output pins.
 

Mitsurugi-w

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I have a ton of blanks that came with my unit. Cool we can make our own though.
 
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