So, if you've read some of my other posts, you'll find I repair arcade games. I also don't like paying outrageous prices for simple parts I can change myself (all discrete thru-hole components), or replacing entire boards if one or two parts will do.
Most recently, I've been repairing an Entropy 2000 Ticket Dispenser (continuous), which is a fairly simple clone of Deltronic models. (Maybe "clone" is the wrong word. Entropy did their own mechanical design, and while it may not be built like a tank, it certainly is a workhorse unit. I have nothing against them.) Anyway, the symptom was simple: tickets would not increment. Similar to Deltronic's original design, the circuit involved here is a photointerrupter, hex inverter/buffer, and transistor with the collector wired to the "notch sense" line in the four-pin connector. Pretty simple. (The schematic is readily available online for those of you curious.)
First guess was the transistor. I had some 2N2222A transistors, so I replaced it, and it worked for a while then quit again. I tried replacing it again, and the same symptom resulted. Clearly, this was strange. The Entropy rebuild kit you can buy from distributors comes with 2N4401 transistors in place of the 2N2222A (okay, this is a fine swap), plus a socket and the inverting buffer, a CD40106BE. It also has a TIP122 (readily available power transistor for driving the motor), and NTE294 (a sub for the hard to find A966 originally used).
Since my initial attempts failed, and I had plenty of parts from the rebuild kit, I figured I'd try the shotgun approach and change them out, having a good feeling that the only part that may help would be the hex inverter. Indeed, there was no change... And actually, the symptom got worse. Now it may only read one ticket before quitting. Physically inspecting the photointerrupter (removing the clear plastic guide, checking it, and reinserting the guide) would let it work once again before running into the same problem.
The original photointerrupter is a SY509, a hard-to-find part with difficult to match physical dimensions. Failing to find this, I went looking for subs. On a hunch, I tried the TCST1202 from Vishay (it was the closest match I could find from data sheet measurements), and lo and behold, it's a nearly perfect drop-in replacement. The clear plastic guide is a little loose, but it fits well enough, and electrically, it's a perfect sub!
Hopefully this tip helps someone else out there; I know it cost me a lot of time to find a match.
