Arcade Collecting > Pinball

Gottlieb System 80b switch matrix question

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brad808:
Hey guys I picked up a Hollywood Heat tonight and am having a problem with closed switches. When I check the switch matrix I'm getting a whole column out (1,11,21,31,41,51,61,71) are all showing closed. Any help as to where to start looking is appreciated. I tried swapping the two circuit boards with the diode strips under the playfield but the problem continued. Would I be correct in assuming one of the matrix ICs is gone bad or possibly bad connection? If so which one should I be looking at?

Thanks for any help and be gentle I'm pin noob  ;D

brad808:
http://www.pinwiki.com/wiki/index.php?title=File:Gtb_sys80_cpu_divided.png

Looking at that diagram I'm thinking there could possibly be a problem with z13 or z14 the switch return ICs? Maybe tonight I can try and swap them around and see if the problem moves to another row?

brad808:

--- Quote from: pinballjim on May 25, 2012, 09:41:43 am ---You need to physically inspect every stuck switch on that column.  You also need to check every diode  associated with those switches.  Any funny business with a shorted diode, stuck switch, or switch touching ground can cause that problem.

--- End quote ---

Thanks Jim I think (hope) I have it narrowed down now. I checked all the switches and there were no contacts, I physically replaced the entire diode strip with another one. That left me with the chips. Someone had previously repaired them. I swapped two of them out of their sockets and the problem moved to a new set of switches. I'm thinking that probably means the solder on the sockets is ok but one of the chips will need to be replaced. Now I just need to source them.

Sent from my Desire HD

ed12:
hi
go slow and follow the advice here
pray it is not a :riot: chip..

ed

brad808:
Well time for me to admit my first mistake with it.... IC z12 and z13 are different chips! whoops, damn letters are so small z11,12 are 4704 series chips and z13,z14 are 4700 series chips. Guess its back to the drawing board.

Right now I have 10,11,20,21,30,31,40,41 etc all showing closed switches

Now if i unplug the j6 connector where all the switches return shouldn't all the switches show disconnected?

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