This is a common problem on TZ and the optos get cooked on the
clock board.Put the game in clock test and see if all the optos
register when the clock hands pass the optos.Keep your eye
on the screen too.Also,If the game has not been played in a
long time try reseating the two connectors located under the
clock this might clear up the error message.

I highly recommend buying the video "In the Zone" at pinrepair.com for $8.00 its a 2 hour video dedicated to getting a TZ machine going, repairing clock and other misc. repairs + has some good humor. There is a lot of time dedicated to the clock, removal, tear down and repairing.

Nice on that video... Thanks.

Do you all agree that getting the updated clock board is absolutely worth the relatively small investment. Mine works great and never give me trouble now.

Make sure someone didn't plug the motor connector backwards on the EMI board under the playfield. Also, clean minute optos with a Q-Tip dipped in Windex. From sitting many years they will surely have a dust coating

Yes, that's actually the first thing to try on these; the one on the right is usually the one of the two at fault. If this fixes your problem temporarily and it returns, get a new connector from GPE.

If this isn't the problem, Martin Reynolds advises to run your clock test for an hour. As things heat up, this will flush out an offending opto and confirm the problem. The 12 o'clock minute opto is usually the offender. Cleaning the opto the test identifies may help.

If the opto is bad, you might want to just opt for a replacement board; as the right optos are hard to find these days, and they're a little tricky to replace.

There are several reproduction boards that are a drop-in replacement for the original. The original clock board almost never works on TZ.

Actually on mine the 6 'o clock minute opto was driving me nuts. Found out it was because the previous owner greased the crap out of the gears with a thin clear grease that melted when the clock warmed up. The melting grease would run down the center shaft of the clock and drip onto the 6 o' clock opto, blocking it and causing a Broken Clock error. I cleaned it a few times with Q-Tip and Windex which would fix it for a couple hours. I finally had to disassemble the clock and thoroughly clean the grease out with alcohol. Works like a champ now, no problems whatsoever and all original from 1993.

This is correct.

They sell upgraded boards with LEDs

That is actually done quite a bit. Its done mostly to keep the housing from cracking from my understanding but can help vent some of the heat out of there. Congrats on the TZ, its a great game and by far my favorite hands down.

Excellent. Now, the #86 lamps inside do generate some heat but so do the overdriven resistors in the opto circuit. You can add LED's yourself, if you like. Pinbits.com sells an inexpensive easy to install LED kit to do just that. All you need are decent soldering skills.

Don't drill the clock housing. This was done in the past to let heat escape but really it just looks bad. In home use I doubt you will leave the game on for 8 hours a day straight, no?

At those rates of use? I wouldn't worry even a little bit.

+1,You could change out that board for the upgraded one in the future.