I’m testing some solenoid driver boards in a Stern Trident. Two boards tested fine. The third board drops the number 4 drop target at start up – acting like a stuck on coil. I can’t get to the coil without removing the target assembly but I’m sure the problem is with the driver board. I diode tested the TIP102 (Q9) and it showed the same as the adjacent transistors. But I replaced it anyway. Still getting the same results.

Could Q3 fail in only one section? What else could be causing this stuck on coil?

Thanks

Bob

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Sorry - yes i meant U3 not Q3.

I don't see much else that could fail causing this kind of problem. Not much else in that circuit.

A bad diode (CR9) wouldn't cause that would it?

U3 pin 3 measures 4.63 volts. I think that's it. I was going to check the other base pins but were in an electrical storm at this time so i quit for the night. Tomorrow I'll check the other base pins and the diode but I think we found the problem.

I understand that chip is no longer available but I have an old SDB that I've been stealing parts from.

Thanks guys - I'll let you know what i find.

Bob

Quick update, I pulled the CA3081 from my old SDB. Then I removed the suspect 3081 from this board. Unfortunately I lost a few solder pads and had to do some stich work. I installed the board in the game and turned it on. This time drop target 5 went stuck on. I ran through solenoid test and target 4 is working fine but target 5 is stuck on. I tested the voltages as Quench suggested:

pin 3 = .86
pin 6 = .85
pin 8 = mV
pin 10 = .84
pin 11 = .89
pin 13 = .85
pin 16 = .84

Pin 8 is the control for target 5. I'm not sure if pin 8 was one of the missing solder pads. I haven't removed the board yet.

When target 4 was stuck on I got 4.62 volts at pin 3 but now i get mV at pin 8.

My question tonight is would a bad solder joint at pin 8 cause it to read mV?
Or do you think this pulled CA3081 is bad?

Thanks

Bob

My meter says mV (millivolts?) - The number fluctuates so much I can't get a solid number. I guess it's showing open. I get the same fluctuating when only the ground is attached. I'll check my connections tomorrow if I have time.

Thanks for the lead on the CA3081's. I'll order some.

I normally install IC sockets but the pulled IC had solder residue on the pins so i didn't use sockets.

Thanks

Bob

I don't think this driver board wants to cooperate. I found a bad solder joint on U3 pin 8. Fixed it and installed the board. Drop targets 4 and 5 are now working fine but now the Eject Pocket (sauser) is stuck on. I checked U3 pin 10 and it's still .84 volts. I guess Q12 is now suspect.

Am I doing something wrong? Could Q12 been bad all along and didn't lock on because the other coils were locked on before?

I seem to be going down the list of coils.

Thanks

Bob

Update: Because the old pulled CA3081 had some solder residue I didn't use an IC socket. And I wasn't happy with my solder stitch work. I got in some new CA3081's so I removed the old CA3081 and installed an IC socket. I put everything back together and it works fine. Three down and one to go.

I installed the third driver board to test. The outhole coil stuck on. I replaced Q16 and now all the coils test fine.

The problem now is the displays have a slight flicker. I'm guessing the trim pot needs adjusting. (C26 is new). As soon as I find my plastic screwdriver I'll check the TP2. 185 volts seems a little high. What do you set the output at?

Thanks

Bob

TP2 and TP4 on the driver board both show 81 volts DC. Adjusting the trimmer pot makes no difference. Then I checked the rectifier board - TP2 shows 81 volts. I disconnected J3 (on the rectifier board) and TP2 goes to 173 volts.

A little background on this board - It's a Stern SDU 100 rev 0. When I got it the trimmer pot was broken. I replaced the trimmer but the hole spacing was not the same so I had to modify the connections. They tone out OK. I'm not sure where I got the trimmer but I think the markings are 25 3M 7845.

Before I replace this trimmer can I check it in circuit? How do I do that?

Thanks

Bob

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Thanks Pins,

Between the outside terminals I have 20.07 k. The new pot I have now on hand shows 23.72k.

The old pot - from outside to center shows 7.1 ohms to 20 k. The new pot shows .7 ohms to 23.72 k.

I think it's in the ballpark. Looks like I got some reading to do tonight.

The only thing that 'looks' suspicious is R51 and R55 look a little toasty. I'll check those later.

Bob

I just checked R51 and R55 in circuit:

R51 = 32.2 ohms
R55 = 8.16 k ohms

Would being in circuit make a difference?

I just compared the resistors on this board to a working board.

R51 = 21.3K working - 32.9 ohms non working (should be 22K)

R55 = 1.2K working - 8.4K non working (should be 1.2K)

I'd say the resistors (at least) are goners.

New resistors and transistors are on order.

I'll post when they are installed.

Thanks

Bob

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Parts arrived except Q21 (hopefully it's be here this week).

Tonight I replaced R51, R55, R56, Q22 and Q23. I installed the board and no change. 80 volts at TP2 and TP4. Turning the trimmer makes no difference.

Displays still flicker.

I'll let you know when Q21 comes in.

Thanks

Bob

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Today the Q21 arrived. I installed it and got the same results. 80 volts at TP2 , TP4, and at the rectifier board.

Pins, you may be right but I only ordered one Q21. I have extra for Q22 and Q23.

What could be causing this voltage drop? I have replaced Q21, Q22, Q23,R51,R55.and R56.

I'm at a loss.

Bob

Can this be done with only J3 and J5 connected?

Thanks Rikoshay, the solder hole is an optical illusion. I have good continuity there.
I'll get back with the voltage readings shortly.

Thanks

Bob

I checked the voltages:

R55 - across = 4.6v ; bottom leg = 1.4Mv ; top leg = 4.6v

R51 - across = 74.5v ; bottom leg = 5.8v ; top leg = 1.3 Mv - I checked each point twice. But the second try on R51 - top leg I got 190 Mv and it was fluctuating (like an open circuit)

Then I checked the banded side of VR1 and get 200 Mv - fluctuating.

Then I checked the displays and they were all dark. I'm not sure but I think they went dark between my first and second attempt at R51 top leg.

Back in post 15 Quench suggested I check the solder connections on C26. I looked at the solder joint on the back of the board and it looked fine. (I didn't check continuity)

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After the displays went dark I pulled the board and took it to the bench. This time I did continuity check the solder connection on the top of the board. It showed open from the + leg of C26 to TP4. I re-soldered the connection on the top of the board and now I have continuity to TP4.

This was probably the problem all along. I just hope something else isn't causing the dark displays now. I'll try another driver board and check the displays. Then I'll install this board and try again.

I'll let you know what happens.

Thanks

Bob

I quickly tried another driver board that was working before. No displays. I have nothing on TP4. Maybe a fuse. I'll check tomorrow.

Thanks

Bob

Thanks Mark, I'm very familiar with his displays - I did the beta testing on his Williams 3 - 6 displays. And I built several Bally/Stern displays. You're right nice kits and easy to assemble. However this is just a spare board I'm trying to get working.

Bob

That power supply was a fun build - I learned a lot. It's still work great. I use it all the time.

I checked the fuse and it was bad. First i tried the known working board and the displays were back. Then I tried this board (the one that's been giving me all this grief). The displays are working with this board also. I just have a couple of solenoids not firing. The biggest lesson learned here is don't go by looks alone. The solder connection on C26 looked fine on the bottom of the board but it didn't come through to the top.

Thanks to everyone.

Bob