Stern Solenoid/Driver Board - RevC

[Sinbad79]

Hi Guys
Last night picked up a Stern Galaxy - powers up, GI lights OK, just not booting.
While i havent had the time to systematically work through diagnosing the electronics, i did notice that the under playfield fuse was removed, i'm assuming becuause the driver board was locking up coils - tested it and yep, that was why.

So i removed the solenoid/driver board - which is the rev-C type and started to test the transistors - herein is my question.
The voltage readings when using a DMM with red lead to GND and black lead to TOP of Transistor are mostly around the 1.4v - the information on the net suggests that these should be around 0.6v.

Do my readings suggest that there is something else wrong on this board or do these voltages sound OK?
Additionally, Q10 on this board (as an example) was reading a lower voltage 1.05v - which is known bad because the pop bumper coil was humming (locked on - reason why under playfield fuse was removed)

Any suggestions?

[Homepin]

I wouldn't bother with EXACT readings as there are too many variables to stipulate a precise figure.

What you are looking for is a SHORT circuit (0 (zero) ohms) between the collector and emitter of the transistor. The transistor acts as a switch and when ON it basically shorts C to E - when OFF C to E read open circuit.

With power removed - if a transistor reads zero ohms between C and E it is stuffed and the coil will lock on as if the transistor switched it on.

That's what you need to understand and go from there.

[Sinbad79]

ok, didn't know that, thats helpful.

[Sinbad79]

Ok well according to that suggestion, all transistors are fine, which begs the question, why caused the coil to burn?

[Sinbad79]

Couldn't modify previous post, so here's another one, lol.

Tonight i spent some time on the machine to take a more systematic approach to diagnosis.
Began with testing voltages on rectifier board, both with J3 connected and not.

Results as follows:
TP.     J3 off.     J3 on
1        5.8vdc.   5.85vdc
2.       146vdc.  218vdc
3.       10.9vdc. 13.2vdc
4.       5.6vac    5.6vac
5.       44.3vdc. 44.0vdc

How do the above voltages compare?
TP3 which converts to the +5v regulated source seems fine, TP4 is low and outside of spec, TP2 seems low (backbox displays dont power up)

Does anyone have any direction or suggestion as to which components on the rectifier board are at fault?
What i'd really like is a components list, so i can replace everything.
Thanks

[Strangeways]

Those voltages look fine.

A fried coil will most likely be the associated driver transistor (TIP102) on the SD board. Even though it measures correctly, it takes 2 minutes to replace it.

[Sinbad79]

Thanks Nino.
I've decided to refresh the board anyway, and upgrade the bridge rectifiers to the larger 25amp version.
I'll also replace the fuse holders, and connector pins.

There is an issue with the displays not working on the machine, so I've replaced the diodes as a precaution as well.
Here's a photo of progress.

[Homepin]

That looks nice - be aware that most of the PCB holes are 'plated through' so ensure you maintain the through board connection.

[Sinbad79]

Yea, will solder both sides of the board where relevant.
Factory solder on these boards is an absolute mess - tempted to completely remove silk screening and solder but wont go to that much trouble.

What rating are the fuse clips?

[studley67]

do not overlook the connector pins,they DO lose their tension.

[Sinbad79]

yea ill re-pin all wires for which i change the connectors/pins.
Shame work gets in the way of having fun....

[Sinbad79]

Thought I'd docuument progress here in case anyone else does the same.
Board desoldered with solder braid and then sanded clean to expose the copper traces. I've done this to help me verify the integrity of the board and tracks.
Next step is to get the DMM onto it and check traces for good connectivity before soldering on the components.

[Sinbad79]

Pins installed...

[Sinbad79]

Next.... Fuse clips.
Make sure they are soldered in the correct way!

[Sinbad79]

Ran out of fuse clips last night so parked the rebuild of the rectifier board for the night and moved onto the M-200 MPU

Board powered up in the Machine gave a solid LED light, so i've pulled it out and powered it up on the bench with a modified PC-PSU to run some diagnostics.
Preliminary tests on the CPU pinouts suggest the VMA voltage is too high and is an issue.
CPU
Pin40: Rest - 5.28V
Pin03: Clock - 2.52V
Pin36: Clock - 2.60v
Pin37: Clock - 2.60v
Pin05: VMA - 3.68v ..... should be 2.8v

I dont have a logic probe so am limited to what i can test - so any advice or pointers would be helpful
Thanks all !