Ok,

Board is blowing F4 5A on rectifier. TIP 102, known good, replaced, collector and emitter shorted to ground when F4 blows.

Checked and replaced all resistors, capacitor, diode on the circuit per schematics.

Parts replaced:

Q7 (TIP 102), C3, R14, CR7, R13, R61.

Have not replaced U1, which is a ULN 2081 A. Suspected issue as PIN 10 is grounded in addition to PIN 5 (which pin 5 is shown in the schematic as being grounded).

Per the schematics, U1 pins 5 (base), pin 9 (collector) and pin 10 (emitter).

Of course, with coil disconnected (old one was trashed, crazy resistance readings, melty), game fires up and plays fine.

Replacement coil in, boom.

I will go to the next level and dig in with a logic probe, but maybe I've already spotted the issue five fuses later?

U1 - pin 10 and 5 grounded.

Bad U1?

Ok.

U2 pin 5 is high (connected to 5V power TP1 & GND) and then pulses low on solenoid 7 test (the affected solenoid).

U1 pin 9 is low (connected to 5V power TP1 & GND) and then the low LED on the probe blanks out...

Should U1 pin 9 be pulsing high? I am going to test the other solenoids on U1 also.

*edit* think I answered my own question, all points on U1 related to the collector element for the chime solenoids do the same thing. Pin 14, 12, 9, 1.

I realize I miscounted pins - on U1, pin 5 and FIFTEEN (15) both are shorted to ground, and this is spelled out on the schematic.

After realizing my mistake, it didn't get me any closer, but yeah. DUH. Learn how to count pins on an IC!

Note: repinned all but TWO connectors (on light board, J4 and J2). All rectifier/SDB/MPU connectors repinned and replaced.

I'm thinking there might be a short to that solenoid. Anyone have any other bits to add, I'd like to hear it. Hate diving into cabinet shorts! LOL

Yeah, the coil was the first thing I replaced, verified that it tests properly as far as resistance and I removed the installed diode, tested, and replaced with a 1n4004 in the proper orientation. No busted windings either.

Ok, but as far as testing U1.... The circuit within U1 I'm testing is basically an NPN transistor, so I'm guessing by diode test, I should be seeing readings like an NPN transistor.

So pin 10 on U1 is base, pin 9 is collector.

I would expect (based on another NPN transistor, TIP 102) that B-C would show 0V on diode test, and about .6V on C-B. Meaning, COM (black) on Base and (not sure what to call it) Red on Collector shows 0V. Reverse, red on Collector and Black on Base shows about .6V.

However, what I'm showing on U1 is...

(Pin 10 base, pin 9 collector)

COM (Blk) on base, Red on Collector: 1.7V (diode test)

Red on base, Blk on Collector: .73V (diode test).

Sure seems to me that the transistor on U1 10 (base), 9 (collector), (emitter connected to 15 along with other emitters as this IC is common-emitter) is bad.

Am I correct?

Another question: why would the probe test be not useful? Is it because the signal being passed to U1 is not really what we're looking to find, but instead if there's a fault in the cascade voltage levels on that transistor within U1?

ULN 2081A schematic (resized).png

...and running a strict VDC test, on SDB board, black on ground, I'm seeing .14VDC approx on pin 9 until the coil fires, and it rises quickly so my DMM isn't able to hold it - but I'm seeing more than .8VDC.

On pin 10, it holds at about .83VDC until the coil fires and then it drops quickly and then comes back up - I think it dropped to about .1VDC, but was unable to hold it.

This is all very good info Quench thank you for your detailed explanations and time.

I'm going to dig into it after dinner to get a better idea, I'll post the info, thank you!

Quench Ok, I didn't have another CV-31-2000 (I think that's the right coil, the machine is buttoned up right now) at the time I was working on this last.

I ordered a replacement "new" coil from ebay, put it in the machine, blew the TIP 102 again as I noted.

Because of my earlier posts - which you answered so well - I didn't bother testing the diode on that coil. I don't know if it's a chicken-and-egg scenario, but the diode on that replacement coil was indeed blown.

Once the TIP 102 was replaced, and the diode on that coil was also replaced, machine powered up, coil wired up, the fuse and TIP did not blow. However, still no chime in test mode on that solenoid (17 on the test - the "extra" chime).

I have double and triple checked the wiring and can't quite figure out one discrepancy.

The CV-31-2000 solenoid has three lugs. One diode from lugs 1-3 (1N4004), and one diode from lugs 2-3 (1N4001 I believe).

The schematic only shows two leads to this solenoid.

However, I have one white and two green wires - the prior solenoid was different (two lugs). I believe (as the coil wrapper was very burned) the solenoid was a CZ-31-2000.

White wire was to lug 1 and two green wires (both trace fine with continuity test) that went to lug 2 on the old solenoid.

I'm wondering if the proper wiring would be for one green to be to lug 2 and one green to be to lug 3? I ask this as there was no action on the solenoid with both green wires tied to lug 3 - and not 100% sure that it should be on lug 3 as the prior solenoid and schematics only show a two lug solenoid as far as wiring is concerned.

It's just not making a whole lot of sense to me right now.

Quench very helpful. Thank you for that. I double-triple checked for other vendors for that coil and all only had the three lug variety. Since I now know how to wire this to the lugs, I will install this without fearing of blowing yet another TIP 102.

I wonder what the design in the third lug is for? Is there no coil winding to the third lug? Or is this a coil with dual winding?

I understand now, thank you.

I am pretty sure that the coil part number I ordered wasn't available, or there was some sort of cross that got me to that part. But in short, I have the wrong part but it can be modified to work.

I have read about solenoid expanders and wondered when I'd get a chance to work on one. Not yet...

So they used solenoid expanders and modified coils because they couldn't fit more solenoid circuitry on the SDB? Maybe two-fold to reduce heat consumption and reduce single point of failure also?

I will post plenty of pictures this weekend.