Thursday, May 5, 2011

TAF repair

Recently repaired a TAF. I actually even had to return as my first repair didn't solve the problem completely. :-(

Issue reported was that sometimes the game gave errors about the bookcase, .. Weird thing is that it didn't happen all the time, only when the game had been played for a while.

Well the problem didn't show up when I was there :( the machine played flawless.
Inspected the boards, another tech had already replaced the connector on the right hand side of the powerboard (J102 if my memory is correct). Maybe to try to resolve the same problem, maybe the game had reset problems in the past. I don't know.
Judging from the condition of the boards, several repairs had already been done to this game.

Measured voltages on the board, everything was ok. Testpoints ok, all leds were on, .. Anyway my guess was that the bookcase error messages were related to the 12v power used for the optos, and for some reason 12v sometimes dropped. Could be on the board or in the wiring.

While checking voltages on the pins going to the playfield, I noticed the connectors at the bottom left of the powerboard were not tight anymore.
There you have J116, J117 and J118. These all provide ground, +5V and +12V to various boards in the game.
One connector especially was very loose. Probably the game had issues with them in the past and that connector must have been unplugged a lot. The metal clips just had lost all their tension and it felt like they did not make a good connection to the header pins.
Checked a few other connectors on the board and they all were in better condition, but not exceptionally good.

Replaced one connector that provided power to the playfield, that's where the optos get their 12v from. Tested the game, still everything worked.. as it was already getting late, and I couldn't reproduce the error, I called it a day.
Instructed the owner of the game that if the issue came back he had to open the backbox and see if all leds were still on (to see if 12v was missing or not on the pcb) and possibly switch J116, J117 and J118 around and see if that solved the problem (the three are interchangeable).

If the problem would come back I could check the rest of the connectors or check out the header pins too. They weren't burnt so I didn't replace them now (usually only GI pins need replacing, not 5v or 12v pins), and I didn't want to remove the powerboard when it was not required as it would further limit the life of the connectors.

A few days later I got an email from the owner, suddenly the dmd display would show garbage.. instructed the owner to reset the grey flatcable. This solved the problem.

A while later I was contacted again. No opto or display problems this time but sometimes the game would just act weird and play completely wrong sounds.

There could be two sources of this problem - either the grey flatcable that connects the cpu to the sound board (the same flatcable also connects the cpu with the fliptronics and dmd driver board). Through the grey flatcable the cpu instructs the soundboard to play specific sound samples. If the data lines have a problem (ie one is blocked) it's possible the game plays the wrong sounds. It was suspect because the garbage on the dmd.
It could also be a problem with the +12 and +5v connectors as some of the boards in the backbox also get their power from these pins, and these definitely were suspect.

Again the problem didn't show itself when I arrived. Swapped connectors on J116, J117 and J118 around and suddenly it did show up. The wrong sample was played, when you would go into the menu you didn't get the typical 'bong' sound but another music. In the selftest the soundboard would play incorrect samples.
With these symptoms you would suspect a grey flatcable, but I got them while playing with the power connectors ? Weird.

Anyway, as these connectors were already suspect I was going to do the repair good.
Didn't have a replacement flatcable with me (later that evening I told the owner where he could order one if the problem would come back). I would start on the powerboard as that was suspect too. Replaced the two other connectors. Removed the powerboard out of the game to replace all the header pins for these three connectors.

With the board out of the game I inspected the backside and I made an interesting discovery. All pins of all connectors had been reflowed ! And I mean ALL of them, even the thin pins for the small flatcable. I have no idea what repair person did this or how long ago it was. It could've been done by the person that replaced the J102 connector, it may have been someone else. I got the impression this Addams Family pinball machine already had a troublesome history.

Finding this made me more suspect about the powerboard and previous repairs. I live by the 'don't fix it if it ain't broken' rule.
Reflowing all pins just shows that someone tried to shotgun a problem, without trying to understand the logic behind it. Else only specific pins related to the issue would've been reflowed. If the game would reset, you only replace or reflow the parts involved. Sound issue ? Same thing. Reflowing everything ? Either the repair person wasn't very skilled, or the issues he was trying to resolve were random and he couldn't reproduce them at all.
It's possible more problems had been introduced by reflowing everything.

I desoldered and removed the header pins for J116, J117 and J118. Installed new pins. Noticed that there was one specific issue with them, one set has one pin connected on the front of the board, while all other traces run along the backside of the board (I believe 5v on J116 to J117, but going from memory here, don't have schematics with me now). Noticed that I had to use enough solder there. When finished I measured continuity between the back of the board and each pin at the front.
On the powerboard there are some pins that have traces on both sides of the board, you have to doublecheck there that you have continuity.
Also measured continuity between the two connectors that are underneath eachother (J117 and J118). But didn't check the trace on the front between J116 and J117.. (only on the backside if the trace had continuity with the pin).

Installed everything again.. now things suddenly got interesting ? :(
The dmd suddenly didn't work at all ? Oops..
Hope I didn't blow up something by accident. No.. just a voltage was missing. (don't remember if it's the 5 or 12v).

Anyway I remembered this one trace on the front. Measured continuity and indeed - it seems one of both pins was not making contact with this trace. Power arrived from the back of the board to one pin, but didn't continue on this pin through the front of the board onto the other two connectors.

Took the powerboard out of the game again, soldered the pins at the frontside of the board to the pcb, measured everything..
Put the board back into the game. Now everything worked correct !
Dmd worked fine, the correct sounds played..
Problem solved and it hasn't come back..

My guess as what the original problem with this board was (before I replaced pins) is that it also had an intermittent contact on one of these connectors. Probably even with the same trace on the front side of the board, as all pins had been reflowed on the backside and that looked good. When the game was off (board was cold) all pins had continuity, but as the machine was played for a while the board and connectors heated up a bit, a pin or the board expanded a bit and broke continuity.

Things I've learned from this repair:
- having a problem with only 5v or 12v on J116/J117/J118 can still make the soundboard work but play incorrect sounds ?!
- always double check and measure continuity in all directions when you've soldered pins.. especially with traces that continue on the front of the pcb!

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