Fried Fish Tales switch matrix

[VeeMonroe]

While troubleshooting a mechanical fault with the Caster’s Club on my Fish Tales, I shorted something with a screwdriver. There was a spark and a bang, and F115 (which is the fuse on the power driver board protecting the switch matrix) blew.

After replacing the blown fuse, I got the error message “Ground Short Row 1 is stuck closed.” After looking at some of the individual row 1 switches, none of them appear to have anything untoward going on with them, and I was not getting multimeter-detected continuity between Row 1 and Ground in the cabinet. My next thought was “Have I fried a transistor or similar?“ So I pulled J209 on the CPU board (which is the switch matrix rows), and even with the switch matrix disconnected I get the same error message. Just to check, I also pulled J207 (the columns) and I still get the same error message - how is this happening with no switches connected to the CPU board at all?

Does anyone have any ideas how to proceed? I have the necessary kit and skills to replace a transistor, but it isn’t clear which one is likely to be blown.

 

[AlanJ]

it will be one of the switch row ics. u18 or u19. maybe both.

 

[VeeMonroe]

For what it’s worth, DC levels (I don’t have a ’scope) are about 2.4V at each pin on J209 except row 1 which is 3.1V and row 4 which is 2.1V.

 

[Ped]

Hmm. Sounds like you may have fried U20 on the CPU board.
This is from Clay's guide:

Shorting the Switch Matrix to +50 volts Coil Power.
When in a hurry, the repair person may make an under playfield adjustment with the game turned on. If the coin door is closed, or the game doesn’t
have a coin door interlock switch, it is easy to short a coil lead (+50 volts) to a switch lead with a screwdriver. This will immediately blow the switch
matrix power fuse (F115 on WPC-S or earlier, or F101 on WPC-95), and fry the ULN2803 at U20 on the CPU board. There is a good chance the 74LS374
at U14 (on WPC-95 it’s U23, a 74HC237) will fail too on the CPU board. On WPC-S or later games, the U20 chip is socketed (but not the U14, or U23 on
WPC-95).

 

[AlanJ]

Hmm. Sounds like you may have fried U20 on the CPU board.
This is from Clay's guide:

Shorting the Switch Matrix to +50 volts Coil Power.
When in a hurry, the repair person may make an under playfield adjustment with the game turned on. If the coin door is closed, or the game doesn’t
have a coin door interlock switch, it is easy to short a coil lead (+50 volts) to a switch lead with a screwdriver. This will immediately blow the switch
matrix power fuse (F115 on WPC-S or earlier, or F101 on WPC-95), and fry the ULN2803 at U20 on the CPU board. There is a good chance the 74LS374
at U14 (on WPC-95 it’s U23, a 74HC237) will fail too on the CPU board. On WPC-S or later games, the U20 chip is socketed (but not the U14, or U23 on
WPC-95).

ooh yes looking at schematics your right. more likely u20 col drivers than the rows

 

[VeeMonroe]

For what it’s worth, DC levels (I don’t have a ’scope) are about 2.4V at each pin on J209 except row 1 which is 3V and row 4 which is

it will be one of the switch row ics. u18 or u19. maybe both.

On visual inspection, both of those still have the magic smoke inside. Given the lack of other leads, I am going to go ahead with replacing them anyway.

 

[David_Vi]

Definitely one of those ICs for the switch matrix. This has happened to me a few times with Black Rose (also WPC89, so same as fish tales).

You'll be ok if the ICs have sockets, it'll make for a quick and easy replacement of the IC. if it's not socketted you'll need someone with board work experience to put a new IC in for you.

Those ICs act like fuses on these games and are prone to blowing if you send too much voltage through the switch matrix.

 

[Pick Holder]

The ULN2803A will be gone. If its not socketed then socket it!

 

[drhex]

If you need help doing this DM me.