(Topic ID: 235444)

CPU/Lamp issue on Zaccaria Devil Riders


By kbliznick

1 year ago



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  • 9 posts
  • 2 Pinsiders participating
  • Latest reply 1 year ago by Quench
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#1 1 year ago

Have a weird issue with a Zaccaria that I can't figure out. Upper level stuff man.

Specific details of lamp issue.
Lamps 6000 and 8000 out. Lamps 7000, tilt, game over and 3000 on the backboard are locked on. Also at random boot-ups it will lock on 1 of 2 different pop bumpers. Sound board works, but sometimes the CPU ready signal is not sent so the sound board sometimes doesn't boot, but disconnecting the ribbon cable to the sound board allows it to boot up and work.

So the lamp issue would look to be standard driver board I/O issues, but it's not.
Replaced the 106 SCR's, replaced the 4050 buffers, swapped out the 4724 decoders.
No change. So I jumped the output signals from the decoders for the 6000 and 8000 lamps and the lights work, confirming everything down the line works. If I jumper the enable signal from one of the other fully working 4724 decoders the 6000 and 8000 lamps light up. So the decoder works just fine, which means the driver board is working correctly and somehow the MPU is at fault. The decoder chips on the driver board all receive 6 signals, 5 of which are shared by EVERY single decoder on the driver board. The only different signal is the enable line.
So this must be a RAM or memory issue somehow as all the 11 other decoders are working fine. Just to make sure on the MPU board I replaced the 3081 transistor array (used as a buffer/amplifier) at IC40 as well as the 4028 at U38 decoder chip for those enable signals. No Change.
Tried a different set of Roms (both stock and Freeplay) as well as a different 2650 CPU chip, No change.

Already swapped out the 6514 Ram with no changes. Need to try the 2101 and 2114 next.

Game is so close to being fully functional, but one little glitch somewhere is tying me up.

#3 1 year ago
Quoted from Quench:

You mean the 4028 at IC36? (not IC38)
What's your logic probe telling you about activity on the input enable signals to those two 4724 chips, and all the way back from the 4028 and the 4556 at IC32 which selects the 4028 chips? Is there activity or are they stuck high or low?
Are any of the outputs working properly on the 4724 chips at IC9 and IC10 on the interface board?

Yes IC36 (not IC38, that is a switch row)

Yes Outputs 2-7 on Q10 work correctly and 0-4 on Q9 work correctly. Jumping the two enable signals together on these 2 chips will get the 2 non working lamps to work (and cause the locked on signals to lock on the lamps in the same output positions on the other chip). The decoders work correctly and have swapped them back and forth in good positions. It's the output from the MPU board, not the hardware output but what the CPU has decided to turn on.

When looking at the order they are in on the schematic one thing becomes obvious. If you look at the previous 3 decoders used for the coils they are listed in order of how they are fired during the coil test. When looking at the lamps with the issues they are all consecutive in the schematic. (this made me think it's an issue with either the ROM or RAM, the positions where the info for these lamps is held is corrupted, it's not the ROM's at this point, still think it's the RAM)
IC10 Q2 Game Over (locked on)
IC10 Q1 Tilt (locked on)
IC10 Q0 Bonus 6 (non working)
IC9 Q7 Bonus 7 (locked on)
IC9 Q6 1st move rider (locked on)
IC9 Q5 Bonus 8 (non working)

SO jumping the enables on IC9 to IC10 will cause the Bonus 6 and 8 to flash and will lock up the lamps at IC9 Q1 and Q2 and IC10 Q6 and Q7. I can take it a step further but don't see the need and cut and swap the enable signals and I'm 100% sure that it will swap out the outputs behavior and make 9 act like 10 and 10 act like 9. So at this point it's definitely NOT a hardware issue with any of the decoders or buffers. The CPU is simply not telling those 2 lights to turn on and is telling those 4 lamps to stay locked.

I'll have to check the outputs on the IC36 chip (already replaced) . It sends 5 enable signals, The 2 to the IC9 and IC10 as well as the 3 solenoid decoders. The rest of the outputs on IC10 and IC9 are working correctly during gameplay as are the outputs on the 3 coil decoders.

#5 1 year ago

IC32 is the last of the logic decoders that I think could cause this ( it controls the enables to the 3 coil decoders and these 2 lamp decoders) After that it has to be RAM or addressing or something odd. Nice to know on the 6514 2114 compatibility. Now what crosses with a 2101? Have plenty of 5101's and I think some 6551's and I thought I had a 2101 but can't find it.

#7 1 year ago
Quoted from Quench:

Both the Philips and Intel 5101 datasheets specify that the 5101 is pin compatible with the 2101.
5101 is a very low power CMOS version of the 2101 NMOS RAM chip.

Gracias!

#8 1 year ago

Eureka! It was a bad 2101 RAM. I had already socketed it earlier as I was planning on replacing it but skipped it when I didn't have any 2101's on hand. Used a 5101 and that fixed all the lamp addressing issues as well as the sound board ready signal.

Sucks that I first tried 3 or 4 more other things prior to this (U32, the 2114 RAM and another chip that had light battery corrosion right above the 2101)

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