Some months back, we had to replace my 12-year-old LaserJet 4M Plus¹ after it fried its formatter board. The printer was never even making it into self-test; it would start warming up, and die almost immediately with a 79 SERVICE code (79 SERVICE (01BF) if I recall correctly), which I looked up and found it indicated a failed formatter PCA board. After some drama involving an insanely good deal on a LaserJet 8500DN that we won as the only bidder (for $199), but on which the seller backed out and lied to try to cover it up, we ended up buying a Color Laserjet 4500DN to replace it. I've been trying ever since to find someone who needs a LaserJet 4M Plus with a dead formatter board.
Today, while checking some part numbers, I stumbled across a web page indicating that on the LaserJet 4/4M Plus ONLY (but not the plain² LaserJet 4/4M), that error code could possibly also indicate a defective cartridge. Well, I was pretty certain it had been failing long before it ever got as far as checking whether it even had a cartridge, but just for giggles and grins, I pulled the cartridge out, put power on the printer (which I'd already stripped of all its accessories and upgrades) and powered it back up.
And it worked.
So then I started progressively reinstalling things. Starting with the toner cartridge and loading paper, then adding the duplexer, the network interface, the PostScript SIMM and the expansion memory. And it still worked.
To all appearances, the "failed" formatter board, given a couple of months of rest, has "un-failed". If it continues to be "un-failed", I guess we now have two laser printers.
"Bring out yer dead printers!"
"Here's one."
"I'm not dead!"
"What?"
"I'm not dead!"
"'Ere. It says it's not dead!"
Of course, there's always the possibility it's a thermal problem, and it will fail again. Then again, maybe all it really ever needed was just to have everything in sight re-seated.
We'll find out, I guess.
[1] Technically a 4 Plus fitted with a PostScript Level 2 SIMM, a JetDirect 600N, and a duplexer
[2] The sole difference I'm aware of between the 4 Plus and 4 is the printing speed, 12ppm for the LJ4 Plus vs. 8ppm for the basic LJ4.