Was waiting to post an update until I had complete victory to declare. Unfortunately I’m not quite there. Replaced the CPU board with the original from the seller. Game fires right up; super crisp picture and sound. The only issue: it was not holding the vertical synch. After doing all of the easy things (trying to stabilize will wl the vertical hold pot, cleaning and reseating connectors, checking continuity from PCB to monitor board, etc) I asked for help on Klov. Rightly, all opinions pointed to needing to recap the monitor.

So: after a week of practicing my soldering and resoldering skills (latter made sooooo much easier wl a Hakko 301; life saver), I finally tackled the job tonight. Biggest bear was physically getting the monitor board out of the cocktail. Once it was on the workbench, replaced all of the caps, reflowed solder on PCB and monitor board connector pins, reflowed solder on the vertical hold pot, and turned the pot several times to both extremes to “clean” them.

The good news: game fired right up and the picture is as sharp/crisp as it was (in other words, patient survived the surgery and was no worse off than before).

The bad news: it’s still not holding vertical synch.

I’m using the replacement CPU board the original seller sent me in place of leaked-battery-fried original. There were issues with battery terminal and CMOS on the replacement board; at this point should I get another board and see if it’s a problem with the signal from the PCB? I don’t have a scope; have not validated that a good signal is coming across.

Any other ideas?

thanks all...
b

Ps: here’s a picture of her caught “just right” between scrolls

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Thanks all. I’ve been fixing up my pins for 20 years, but was always too scared to do board work. Adding this Robotron forced me to get some better gear, take the plunge, and just practice. In a weird way, really glad there were issues so I could bring her back to life (and up my repair game). Plus: fun to learn about 80’s CRT’s.

It’s a Wells Gardner K4901. Checked the flow chart. Ordered new IC301, Q301, and a new vertical hold pot for good measure.

Just curious: what would it look like (when) if the vertical synch is working? Stable pic from power up? Or would it just stay put once I fine tuned the vertical hold pot? I was fooled after the recap; screen stayed in place for long enough to get to wave 12 or so in a game. Then started its scrolling ways again.

ps: my original plan was to keep the goodie bag intact. But as I‘ve been dealing with the various issues, carefully opened her up. The various schematics and assorted manuals have been beyond helpful. Also included a nice note from Williams re: difficulty setting to maximize earnings, with a target average game time of 1:30. Made me smile, as back in the day I’d drop 1M+ marathon games at my arcade all the time. My 10 year old self was definitely not helping Pfenny’s arcade’s bottom line

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All: happy to report that the NIB Robotron cocktail has been fully brought back to life!

This past week I finally got a monitor test pattern generator and confirmed that I got a clean lock on the K4901. Pointed towards the spare board I got from the seller to replace the battery-damaged CPU.

Removed, cleaned, and resoldered the 7402 positive sync chip, reflowed all of the connector pins again, checked continuity of vsync back to the CPU. Did the old TV repair trick of leaving it on for hours and seeing if any of the chips were warm to the touch. Nothing out of the ordinary (RAM and the 8-bit shift registers serving them; not "hot", just warm). No luck.

Finally ordered a known-working spare CPU board from Andre at Arcade Shop. Arrived today, dropped it in, and: voila! Immediate lock. Resized the screen and have an absolutely perfect machine! I'm sending the faulty board to Andre for him to fix; tactically to have a backup, but: also: because the engineer in me really wants to know root cause.

Realized I never posted the videos of the unboxing; here they are in all of their glory if anyone is interested:
Original unboxing: https://vimeo.com/441652390
Opening the table top for the first time: https://vimeo.com/441652390
Initial inspection of boards/monitor/etc (including the dawning realization that the CPU was hosed): https://vimeo.com/442105933
Continued initial exploration of the guts: https://vimeo.com/442106084

Thanks all for the advice and encouragement; love that not only is a museum-quality Robotron back to its full glory, but: also the crash-course in arcade repair that the three weeks of triage and attempted fixes has given me. @omegamanxxx from Klov (the original seller) was phenomenal throughout the way, even paying for the replacement board to get her back up and running. LOVE when this community comes together; truly incredible stuff.

All the best...
b

ps: for anyone who finds this thread: the answer to my question of "what does it look like if you have lock?" is: a screen that is immediately centered and stable at boot. With my faulty vertical synch, I'd have to wrestle with vertical hold pot trying to get it to stay in one place. Only to have it slowly start rolling...sometimes immediately, sometimes in the middle of a test game. Functioning vertical synch isn't a gradual process of "coming into focus" or "moving into place"...if it's working, it's there (at least from my experience).