Buy a OSB-10B made by GLM.
Best $70 you'll ever spend. Has LEDs that show you if it's a bad receiver or transmitter.
COuld possibly be the board itself.

Fix it and forget it. Good luck!
D

There's multiple opto boards. I believe the right ramp is it's own opto board as is both of the "pb" sensor. And then there is the main opto board. I wish I could be more help here. When I have the occasional "switch 26" error, I simply disconnect and reconnect the board and it fires right back up. Maybe give this a try? I am assuming since disconnecting and reconnecting works, that means the board is slowly going out.

http://www.greatlakesmodular.com/index.html?http://www.greatlakesmodular.com/products/pinball/osb10b.html

I had a similar issue with my TZ and it ended up being a wire that had come loose so the circuit was not being completed. Make sure you check your switch matrix and so if maybe a row is out you can track down the short. I am close by you so feel free to ask for any other support and I will do my best.

Do the easy stuff first. Check the connectors for the optos under the playfield.
Those little disconnects may just need to be re-seated. Simply unplug them and re-connect during switch test while checking for operation.
I had two switches on the Powerfield which weren't registering - tracked the problem back to the connector. I may re-do the Molex pins just to make sure the problem doesn't re-occur. Problem solved (and solved simply) for now.

I'm not discouraging the purchase of a cool diagnostic tool but there are simpler ways if you're not doing this type of work often.
http://techniek.flipperwinkel.nl/wpc/index3.htm#opto

The longer I think about it.......I'll pose a question.
How often does an "opto" actually go bad?
After all, it is a paired, specialized, LED combination. LEDs take a pretty serious beating before they quit so I'm genuinely curious as to how often these LEDs actually fail. It seems to be the "go to" repair advice for a TZ - "check the optos" - yet I've rarely found the optos to be at fault unless they're just dirty.
I'm willing to guess that a little cleaning may help out too. The gumball area tends to collect a bit of dirt and dust. Recently, I had that area apart and it was pretty filthy under the escutcheon. I wound up dis-assembling and washing the gumball machined while I was at it - lots of black dust.

Clean the trouble optos with a cotton swab and some 90%+ rubbing alcohol.

Barring that, get out a multimeter and put it across the contacts of the trouble optos. See if you can find out if it's the actual optos that aren't firing or if it's the board.

For the actual semiconductor? Very rarely. But vibration in the areas optos are located can take a toll on the connections both internal and external after 15+ years. Optos are relatively cheap and easy to re-manufacture anyway so it seems like its less hassle to replace them most of the time.

For the following tests, set up your multimeter with the machine off. Do the tests with the machine on. Turn it back off between tests as you do setup.

An opto switch is made of two parts. A photo-transistor and an ultra-violet LED. One side is the LED and the other side is the photo-transistor. Make sure the to clean any dirt away that would obstruct the light beam and make sure the LED and photo-transistor are proper aligned first. Proceed with these tests if that doesn't work.

1) Use your multimeter to check if current is flowing through the diode. If yes, go to (2). If no, go to (1b).
1b) If no current flows through the diode, put a 1k resistor in-series with your multimeter. Keep the multimeter in current-reading mode and connect it parallel to the LED. Are you getting current?
Yes) Replace the opto. The LED is bad.
No) The opto board is not supplying current to the LED. Fix or replace it.

2) Check the photo-transistor Emitter-Base voltage. This is done by connecting the leads of your multimeter to the transistor's emitter and base. Break the invisible LED beam a few times with your finger while watching your multimeter. Is the voltage toggling?

3) Set up your multimeter to check the photo-transistor's current on the emitter. Break the invisible LED beam a few times with your finger while watching your multimeter. Is the current toggling?

If (2) or (3) shows no toggling, then there's either a problem with the transistor or the opto board. Most likely the transistor. Further tests hinge on whether or not the photo-transistor is NPN or PNP, which I don't know right now.

I thought i had an optos board issue too but when I checked the switch matrix I found everything was out and it took some checking but I found the shorted loose wire. Once connected everything sprang to life.

Hey 27dnast it was great meeting you on Friday. How has TZ operated since we found that Diode that was shorting against the buy in switch. Any other switch errors since then or did that seem to get rid of the gemlins?

Pretty sure GLM are selling the opto boards again, just ordered one yesterday