Galaxian PCB troubleshooting

Scott C

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I am finally starting to go through a pile of Galaxian boards and have a couple that are being weird. I have confirmed the two sets of character PROMs and Z80s are all good. I used my PROM burner to compare two sets of AUX PCB PROMs (to MAME sets) and even burned a new set. However, the two Galaxian boards don't show more than a screen full of "H"s or "8"s, depending on which AUX PCB I use (not any graphics of any kind or anything before this is displayed). It pulses quickly, so I assume the watchdog is resetting it. This is happening on both boards. I am testing on my JAMMA bench and recently replaced the two large caps on one Galaxian board, since they were leaking. I can't find my TEST PROM at the moment and don't have any more 2716 to burn another.

I have been hunting through the troubleshooting manuals and haven't seen anything that matches exactly what I am seeing.

My next plans are to piggyback the soldered-in 2114 RAM in row 3 to see if that changes the start-up screen any.

Thoughts?

Scott C.
 
Check the two sockets that the daughter board plugs into.

Also check:

Corroded/rotted/broken legs on mask ROMs
ROM sockets on the daughter board
ROM sockets on the main board
CPU socket

These are all common failure points on that board.
 
...in other words get one of my galaxian 4-1 switchable kits that eliminate the CPU and ROM sokects from the equation for use in debugging =-P
 
...in other words get one of my galaxian 4-1 switchable kits that eliminate the CPU and ROM sokects from the equation for use in debugging =-P
In working on Pac-Man boards, I do normally replace those sockets, since many are bad. However, I didn't make that same assumption for Galaxian and hoped someone had seen that particular issue before and could point me to a more direct solution.

I'm all ears about the 4-in-1 kit for debugging, so do tell. I have installed 4-in-1 hacks before, but not kits and none with debugging or troubleshooting capabilities (I am thinking of the ABC kit for Pac-Man boards).

Scott C.
 
If your interested in Marks kit you should PM him directly. There are a ton of sockets to replace on a galaxian, the time it will take to do all of them you have wasted enough time to pay for his kit.
 
Bearing in mind that similar symptoms can be caused by different faults, here's a rather old entry from my Galaxian repair log:

Symptom: Board powers up but displays a screenful of H's that *very* briefly 'flick' to garbage every second or so

Diagnosis: Took a heck of a long time to diagnose this, but it was observed that pin 3 of the 74LS245 at 5J was dead and pin 17 of the same chip was High (as measured with a logic probe). Pin 3 (signal VRAM3) connects to pin 14 of the 74LS157 at 3K which was also dead. I replaced the 74LS245 – no change. I replaced the 74LS157 – no change. I then used the schematics to check out all the interconnections between the 74LS245 and chips it directly connects to – all were okay. I then went on a wild goose chase checking on other signals to and from chips directly connected to the 74LS245, then decided to check out the connections from the 2114 RAMs at 3F and 3H. There was no connection between pin 14 of the 2114 at 3H and pin 14 of the 74LS157 at 3K – I really should have checked this before but simply didn't notice that there was another VRAM signal. Anyway, the fault was down to a slightly damaged track/pad for pin 14 of 3K on the board itself (someone had once soldered a socket for this chip and as this board seems to have very fragile tracks/pads it obviously damaged it). So I reconnected the missing link and the board fired right up! Note: I also used the Galaxian test EPROM to check this out along with a Fluke 9010A Troubleshooter. The test EPROM indicated that there was a problem with the VRAM as did the Fluke, so they at least helped pinpoint the area of affected RAM.

Cure: Re-made the dodgy connection between pin 14 of the 74LS157 at 3K and pin 14 of the 2114 at 3H.
 
Thanks for the follow-up. I checked those spots on my board and they all look beautiful. I am going to pick-up more 2716 PROMs and burn a TEST ROM hoping it will point me in the right direction. I did try piggybacking the 74LS175 just to see if it would make any difference at all (didn't).

Scott C.
 
I did PM Mark, but he has never PMed me back with details, a web site link, etc. I am still interested.

As for one of the boards only showing a screen full of Hs. It is now fixed.

Problems:
---------
Screen full of all Hs, watchdog is tripping and causing the screen to flicker quickly. Would occassionally show something else or pause for a moment before resetting.

Solutions:
---------
- Found the SN7404N at 1E had a poorly repaired leg, so replaced.
- Found the 74LS245N (A) at 5J was stuck, so replaced.

The game now boots and plays fine.

ScottC.
 
Here is what Mark told me about the Galaxian kits....

I may have some of those old boards left, but I'm planning to do a multi-galaxian in the style of 6pac in the nearish future, that'll be a little more polished than the switchable kit.
 
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