Black Jack
Bally, 1978I have a bally Blackjack, and I just put a new rectifier board in. I have all the correct voltages at the rectifier board and I have a known good driver board. The Altec MPU only has .8V at the +5v on the MPU and at the zero crossing I have 21.8V.
Where do I follow voltages to figure out whats going wrong.
But I know the Driver board is good. I tested it in my ST.
Which revision Alltek MPU board do you have? Different revisions use different numbering for the test points...
Regarding Zero Crossing:
Rev D should read 43V at TP5
Rev J and K should read 43V at TP7 and 21.5V at TP5
Rev L should read 43V at TP2 and 21.5V at TP6
The 43V used for Zero Crossing comes from the rectifier board J3 Pin12. It goes to Pin15 of J4 on the MPU board.
Alltek MPU boards J, K and L have a fuse on the +5V line, so:
Rev D should read 5V at TP3
Rev J and K should read 5V at TP6 and also after the fuse at TP3
Rev K should read 5V at TP1 and also after the fuse at TP4
+5V comes from pins 13,14,15,16 and 17 of J3 from the SDB to Pins 16 and 17 of J4 on the MPU board.
The Alltek board added some very nice features including a local 'point of use' over voltage protection for the 5V line (they put this protection where it belongs). If it detected too high of an input voltage - this will 'crowbar' (short circuit) the 5V line which will purposely blow the onboard F1 fuse and cut off the 5V signal. Is fuse F1 blown? If so, your solenoid driver board may be putting out too high of a voltage.
The Alltek over voltage threshold is set at 5.7V (which is a decent choice). 5.7V and slightly above is still a useable (but not real safe) voltage which may be why the ST board still worked but may have tripped the Alltek over voltage circuit.
Another update. I believe I have rev L. Zero crossing is at 21.6.
The fuses are all good and I was testing my driver board on another Altec board in my star trek.
I took the entire set up and put it in trek. The game booted and played flawless. The driver board, mpu and rectifier worked in perfect harmony in star trek. It just shows no signs of life in black jack.
At tp1 and tp4 it shows .8v. I am very confused why it says over voltage when the voltages is so low.
I am betting you have bad connectors. Have you rebuilt all of the back box connectors? The originals go bad and were only rated for about 25 insertions.
Quoted from the96stang:Another update. I believe I have rev L. Zero crossing is at 21.6.
...
At tp1 and tp4 it shows .8v. I am very confused why it says over voltage when the voltages is so low.
Your zero crossing voltage at TP6 is good.
Over voltage indicator on the Alltek is intended it show when the over voltage protection circuit has activated.
in real life - it merely means the 12V power exceeds the 5V power by a certain threshold. I think this should more correctly mean "Bad power" rather than over voltage.
Side note - I think they have the over voltage indicator drawn correctly on page 2 of their schematics. It should light when the 5V line is shorted by SCR1or fuse F1 is blown - in order for that to happen, the LED must be facing the other direction.
When the overvoltage crow-barring does trigger, it shorts your 5V to nearly ground. Fuse F1 on the alltek board *should* blow. This would result in TP1 going to 5V and TP4 approaching zero. Doesn't sound like the case for your board.
In order to rule out whether or not the problem is a bad connection - what do you get for measuring 5V on the driver board?
Compare the Alltek TP1 voltage to your driver board's TP1 voltage.
Another cause can be excessive current draw - which causes excessive heat on the driver board's LM323K which then shuts down.
This can be caused by a myriad of issues.
It might also be worth disconnecting everything else hanging off the regulated 5V circuit. That means disconnecting all the displays, and J4 from the Lamp Driver Board. That way you isolate the 5V supply between the SDB and MPU only.
But yeah, the fact the SDB works in another machine is noteworthy but like everyone has said you really need to measure the 5V source at TP1 on the SDB to get a better picture of what's going on.
Quoted from the96stang:It was the connectors. I bit the bullet and rebuilt them all on the mpu. It was a PITA. Lol
You will learn that on an early Bally you always rebuild the factory connectors in the back box as part of a restoration or repair. If they are 30 years old they are bad or will soon go bad.
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Enfield, CT
Melbourne