That, or the EEPROM on the board is starting to go flaky. The programming data for the Quantar is stored in "Non-Volatile" EEPROM, and requires no battery backup. I've never heard of a station losing it's programming like that, but the first thing I would suspect would be the EEPROM itself.
This is different from the station firmware EPROMS, which are likely OTP one-shot type things in the case of this board, which by the way, looks to be fairly old.
It's also possible that you have capacitors that are going out of tolerance and/or leaking. The Spectra series mobiles suffered from leaky capacitors, but they aren't the only Motorola product that experiences this issue. I have TTOMI cards from Centracom dispatch consoles that have leaking capacitors. I wouldn't be surprised if certain Quantar boards did the same thing.
If you power up the station and leave it on for a while while it's in la-la land, and then reboot it, does it start to work without having to be reprogrammed?
My suggestion would be to take a look around on eBay and see if you can find a replacement Station Control card. That should solve all of your problems. Preferably something like an EPIC V card, though that model is pretty new and I haven't seen any on eBay. Be careful of what you buy, though. Some very old Station Control cards are VSELP digital and not IMBE, and others are for DSS-III or DataTAC stations, and still others are analog only.
With regards to your "non volatile memory simm", the others are correct. Firmware was initially offered for these boards in the form of OTP EPROMS, like you have. Later versions came on a SIMM, and you removed the OTP EPROMS and installed the SIMM to upgrade the firmware.
Once you get the thing working reliably, your second move should be to get rid of that ONAN power supply you have in there before it flames out on you
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