if it's not plug connection issues and it really is an 809B (vs it just has a serial plate that says that ... a pic of the front of the machine helps), then there's two switches in the payout circuit thru the reels that would kill powering the payout relay on a win:
coin relay : switch with brown (60-1) and brown/yellow (63-3) wire on blades. Switch should be closed when coin relay reset (after spin, before playing coin)
handle release relay : switch with 63-3 and gray (90) wires. Closed when handle is locked.
either of those two switches being open causes no pay but the handle will release on first coin played and you can spin.
if you are a believer in schematics, paperwork for the game is on
https://bingo.cdyn.com/slots/if there's nothing obviously wrong, then it's probably voltmeter and/or jumper wire time to find the issue quickly. Do you have either?
I assume from how ya phrased the problem you went around the entire machine checking/adjusting/cleaning switches rather than just looking at switches in the problem circuit? If so, nothing wrong with that, ya just have an oops someplace - usually lack of switch blade overtravel so it looks like a switch is closed but it isn't.
it's also possible the payout counter isn't resetting so you'd only get a pay that is higher than any previous pay, and eventually no pay at all.