Alright, I've reached the point of confusion and need some help as to what to do next on the Comet I'm working on. I've got two separate issues, a switch matrix issue and a special solenoid issue.

Switch Matrix Issue: Originally the game was missing the transistor and single resistor below IJ8 for column 5. Column 4 wire was disconnected entirely. There was obviously some burning issues in this area and SR9 resistor bank was a little toasty as well.

What I've done: Replaced transistors and resistors in both column 4 and 5. Also replaced SR9 and SR8. Put the wire back in the IDC on column 4.

Column 5 works perfect now. However any switch activated in column 4 activates all switches on that row. Removed the connector and tested using the in-game switch test and jumpers to isolate that it is in fact a board issue. As I'm not really versed on logic probes yet my next step is to just keep going up the chain replacing things (which I know isnt a great idea but I'm not sure what else to do). Next up the chain would be U45 (a 74LS244), then U15 (a 6820/6821 PIA), then over to U51 & U52 (MC14011) and finally SR16 (another resistor bank). Any ideas here?

On to the special solendoids: Again, there was some burning here and I have replaced one TIP102 that was shorted and two of the pre-drive transistors. All test fine now. In addition, an entire trace running from the center of one transistor to the connector pin was removed/lifted and I bridged it with a jumper wire. (I believe this was the right kicker).

The right kicker locks on when the game is turned on. I removed the diode from the coil under the playfield, tested it (tested fine), and then replaced it. At the same time I removed a wire from one lug of the coil so I could test the other 5 special solenoids. Both the left bumper and bottom bumper do not work when manually pressed. I havent checked the voltage on them yet as I had to get some sleep last night but that's where I'm at right now. Looking at possibly U6 and U7, appears they were already replaced at some point but perhaps incorrectly (wouldnt surprise me with this board)

Last issue, the K1 relay activates and never deactivates when the game is powered on, so you always have flippers even in attract mode. I tested the transistor for this as well and it tests fine.

Any help is appreciated, sorry for the novel.

Mid day bump

It's not a whole column getting activated, when any switch in col 4 is activated it triggers all switches in that row.

Ie. I jumper col4/row1 switch and ALL switches in row 1 activate.

Good info, unfortunately I don't have a logic probe and apparently buying one local seems a bit of a challenge. Think I'll order the u45, u6, u7 and go from there. Thanks guys.

Well u45 isn't the problem to the switch matrix issue...

So now I've replaced sr8, sr9, resistor for column 4, transistor for column 4, and u45. Still any switches in column 4 activate all switches in the corresponding row. What to do what to do...

So the good news is, after replacing U6 and U7 all the special solenoids are functioning correctly and the flippers no longer work in attract mode. Yay. All I have left is this switch matrix issue.. argh.

Considering all of the parts I've replaced so far were either burnt crispy or missing entirely save u45 (which is now conveniently socketed) I'd say I'm doing okay without a logic probe in my possession yet but thanks for the advice. Nothing has been replaced as guess work except u45 up to this point and its now socketed so that's a good thing.

Offering advice on how to test the ICs you mentioned using a logic probe would be more helpful to me.

Nope, it's empty.

Well I've got a logic probe on the way along with some other items so ill revisit this next week once it arrives. hope its not the PIA as theyre out of stock at GPE. Thanks as always for the help guys.

Pin13 of u15 pulses. All legs on u51 and u52 are stuck either high or low. Nothing on either chip pulses.

Didn't have much time to mess around with this thing last night as my wife came down with the flu (booo!). Anyway, I did have some time to read up a bit more on the testing and jumpering connectors to simulate switch closures while checking inputs and outputs and what not.. I think I have a plan for how to test these ICs now before just yanking them out.

Thanks for the help guys.

F it. I just socketed two new ones as it would have taken me longer to figure out the testing procedure than to replace them. Feel free to judge me, however, after putting new u51 & 52s in I still have the same old issue.

And the final repair list, for those that were curious.. fully working now.. not repaired by me.

6810 RAM IC and 24-pin IC socket (audio section). 7402 IC. 2x 2n3904 transistors. 2x 1.5k resistors. 2x 2n4401 transistors. 2x TIP122 transistors. 8 broken traces repaired. 10uf/35v, 22uf/50v/105c, 470uf/25v/105c and 4x 100uf/50v/105c capacitors. 8x 27 ohm 5 watt power resistors (lamp section).

well they were already repaired and testing with good continuity.. they were really just "repaired professionally"..