universal 8116 game not working

[puckhead]

i have a uni game not working, 8116 board, yellow dot PS .  didnt boot up, but  got it to work for a few minutes by pressing the ram clear, but it took a few tries.  the battery was near dead, i replaced it.  now it doesnt boot up.  power supply checks good. i get 5.01 Dc at pin one, but only 4.8 at the logic chips.  seems a bit low.  i dont know much about z80 cpu but will it reset and boot with 4.8? also, one time it booted up with a code 11.  voltages on pins 6, 8 ,and 12 are all about half what they should be, as referenced to ground .  i am a little confused by the PS schematic.  the 24 v and 9.5 V are 2 separate taps on the transformer,  and it seems testing that AC voltage to ground doesnt make sense.  a previous post i read said pin 8 should be 9.5 AC to ground.  i dont get that. am i missing something? all the bridges test good, i did replace the smallest one, but it tested good.  the line noise filter was nasty, and i bypassed it.

can the board be bench tested? i repaired dozens of pinball and other boards, but nothing like this.will it bench test with just 5V and ground? not even sure when to hook that up.

thanks
mike

[puckhead]

i should have stated most of the PS checks good., except the 3 pins i get 3 pins i get about half of whats spec'd.  when it did work, i pressed the ram reset, and after a few seconds got a tune from the speaker. now its just low white noise from the amp.

thanks

[puckhead]

this thing is making me lose my mind. every AC circuit on the power supply plug has a hot( load) , and a return, except the 9.5v AC on pin 8. pin 8 traces back to the return on the 9.5 ac part of the transformer. there is no pin for the load( hot) side of the transformer on the 9.5v side. the load only goes to the two bridge transformers. the 24v ac  has a hot pin and what they call a ground( really a return pin on AC)  pin.  the 100v ac also had a load and return. the 9.5 v ac doesnt. i cant explain that, or how  you could measure 9.5 volts AC to chassis ground.

i may be chasing a red herring, as it doesnt boot, no sound, no displays. i dont even know if the 9.5v ac is needed to boot. i do know its needed to prevent a code 11.  i'd like to bench test the mpu, to at least check reset circuit and address lines on the processor chip to see if it even boots.  in the end i may have to mail it someone to test in their slot, if someone would be willing to do that.

thanks much
mike

[Jim]

was the battery  on a board that plugged into a socket?  these have corrosion all around (green crud)  either  that or the battery area on the board itself.  If the battery circuit is not working the board won't work either.  from what you described I'll bet your problem is in and around the battery circuits, best way to find is to use a meter and do resistance checks point to point.




Jim

[puckhead]

the battery was soldered to the board.  there was very minimal leakage . its very crowded in that area, and its possible there could be some bridging under an IC, but ive seen much worse. i have tested the traces in that area and there are no breaks.  it could very well be the cpu, but being not especially valuable machine, its hard to justify buying a cpu or power supply to try and see what happens.

anyone have a PS or cpu if i need one?

thanks

[UNIMAN]

Not really sure how to measure the 9.5v ac.

Look at page 75 of the Universal Manual. The 9.5vac is sent to the main logic board to sense low incoming voltage. And also look at page 74 and read the power-up delay circuit.
The mpu needs a steady, clean 5vdc supply to stay operating. On top of the power supply is a voltage regulator that maybe the trouble (just guessing here).
If your seeing an accurate 4.8vdc than that's a problem.

Just as a precaution, remove the mpu rack in the machine and check the wiring behind it for foreign objects such as small screws, etc. Also check the big black connector going from door to machine. It sits in front of power supply. Look for any pins or pin sockets shoved down. In the past I've had these simple problems drive me crazy looking at mpu boards and power supplies.

Jim

[puckhead]

i get 5.01 dc at the ps. but it drops to 4.8 on the board. could be something on the board drawing too much current and puling it down, or a weak PS. also, i previously did check the reset circuit while bench testing and there is a problem there. i rigged a temp manual reset, and using it did reboot the board and the cpu did show activity at the address pins. its hard to trouble shoot the board because the schematics i downloaded are too fuzzy to read, the scans arent great.  its a pretty machine, one id hate to give up on, but its doesnt have a lot of value. are cpu boards available? also , if you have a universal , could you check the ac voltage from pin 8 on the PS to ground?

thanks
mike