Discs of Tron Upright

[karlcdoe]

Symptom: Game completely dead.

Discovered a short on the 12v line when pcbs plugged into loom, removed the ribbon cables between pcbs and perhaps rather obviously the short was on the super sound io pcb. This cab had a switch mode with overload protection fitted therefore the psu shut down, on an original PSU a fuse would probably have blown instead.

Looked for what used 12v on the schematics and I was about to start removing/testing ICs but a little online research led me to lift the legs on CP20, 172, 204 as they all tested shorted in circuit.

Fault: shorted tantalum 10mF cap at CP20, replaced with an electrolytic.

Symtom: Missing sound channels but sound on both speakers
SSIO pcb w/panning was fitted in error, replaced with standard SSIO

EDIT:

I later discovered that jumpering the board into 'environmental' mode will also restore the missing sounds but they will be now mapped to 'front' and 'rear' speakers rather than 'left' and 'right'.

Symptom: missing sounds during interlude sequences, player 1 button not wokring but works in test mode, test mode reports 'upright' but had all the port and lamp test menus for EDOT

Environmental Discs of Tron program ROMS fitted, replaced with 4 x upright ROMS.
karlcdoe2017-10-13 13:55:50

 

[DanP]

Nice fixes Karl. Does that mean there's an SSIO with panning going spare?

Dan

 

[Judder]

That's funny - we must have been working on very similar problems at exactly the same time

https://forums.arcade-museum.com/showthread.php?p=2438375

In my case the choke / inductor had burnt out as well on the Super CPU board (L116 is the connection to the 12V part of the circuits so that had died).

CP20 on the Super Sound I/O board was showing as straight to ground, but after I removed it it tested fine as a 10Mf Capacitor so I looked at other 10Mf Capacitors on the same circuit

CP204 and C172 were both shorting to ground, so I removed one side of C172 and tested the capacitor and it was a short-circuit so that was definitely dead and needed removing

I replaced it with a modern 10uF Capacitor (same capacitance, just a modern way of writing the micro-farad unit) and now all of the above 10Mf/10uF Capacitors reported capacitance, about 4.5Mf / 4.5uf, and no shorts to ground

I'm still interested in the designation in the Midway schematics about the difference between CP labelled capacitors and C labelled capacitors if anyone knows?

 

[karlcdoe]

That's funny - we must have been working on very similar problems at exactly the same time

Interesting... seems the tantalum caps are a pretty common failure point, in fact I had shelved some other MCR pcbs that had partial/total shorts I suppose I ought to get them down and check the caps.

I haven't re-checked but I take it the 'CP' designation is not for tantalum caps or somthing.

 

[Judder]

I haven't re-checked but I take it the 'CP' designation is not for tantalum caps or somthing.

That's a good call, and I thought similar but then if you check on the 12V part of the sound board (the largely middle bit) both the CP and the C capacitors seem to be those strange tantalum caps - as in the picture above showing CP204 and C172 - weird!

Here's a quick schematic circled for historical reference on the thread