Bally 6803 mpu boot issue

(Topic ID: 227064)

Bally 6803 mpu boot issue


By mrsodapop

68 days ago



Topic Stats

  • 10 posts
  • 4 Pinsiders participating
  • Latest reply 53 days ago by mrsodapop
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#1 68 days ago

Hi all,
Got a Bally Party Animal that will not boot(this is a new problem, game was working good). Upon boot up I get 3 flashes from led. According to Pinwiki, there is a RAM issue. I installed NVRAM sometime ago, but got a replacement and installed with no change.
I then pulled MPU and connected to test bench, and had a friend burn Leon's test chip. When booted up with test chip, led just lights and stays on steady. I then started going through Leon's test procedure. Removed both eproms(U2,U3). Checked Reset signal-OK, next checked Clock signal Supposed to be 1v @ U1 pins 2/3, got 1.2v @pin 2, and .5v@ pin3(?) I thought this was odd, and rebuilt the whole clock circuit(crystal,C2,3,4,5) with no change upon retesting. Decided to continue on- checked address lines and all seems good. Reinstalled test eprom, and checked U3 eprom signals. Here is where I get confused, the test procedure says I should have .5v @ U3 pins 21,23,24, I got 4.2v. Now these 3 pins are connected to pins 26,27,28 of U1 cpu. In previous test procedure, it is stated I should have between 2-4v at U1 pins 21-40. So If U1 pins 26,27,28 are supposed to be out putting 4v, and are connected to U3 pins 21, 23,24, how are they supposed to test at .5v?

Also replaced ICs @ U5,U6,U9,U10. Still no change. Test eprom still will not flash boot led, nor will reinstalling game EPROMs get it to boot past 3 flashes?.
Can someone help me find what I am missing?
Many thanks for any ideas
Aaron

#2 68 days ago

Sounds like a bad 6803 @ U1

#3 67 days ago

Are any of the traces damaged from alkaline corrosion?

#4 67 days ago

You generally don't want to stick probe leads on XTAL and EXTAL pins of a cpu that is using a cyrstal setup like in this board. The crystal circuit is really sensitive and you will likely stop the oscillation by doing so.

The real story about if the clock is working is the 'E' pin on the CPU. 'E' is the external clock and you can safely probe this. Ideally you want a DMM or scope to check the frequency of the E pin. It should be right at 0.895mhz. VDC reading of 0v or 5v is an indication the cpu or the crystal is not working. The schematic i am looking at is hard to read but I think the 'E' is pin40 of the 6803 chip.

For the RAM chip put a logic probe on the /CS input at P18. When you power up the game it should go high briefly then start pulsing. If it never pulses or reads 0v or 5v always during the power on self test routine i'd check Q6(if always low or 0v), U9, and D6 (if always high but pulse at U9 P6).

U5 U6 and the 6803 must be good too. If you did any soldering work around those chips I'd be double checking it. You should be able to check U5 U6 by pulling the ROMs and PIAs out of the board. Power it up and all address/data go active so then you can check for pulsing on the output sides of U5 and U6.

Make sure the ram chip has power too at P24. Schem shows it P24 of the ram connects to V_AUX which i can't find on the drawing right away. Usually that means it is tied to the reset section... but should read 5v.

#5 67 days ago
Quoted from snakesnsparklers:

Sounds like a bad 6803 @ U1

I keep leaning towards this too.

Quoted from Atari_Daze:

Are any of the traces damaged from alkaline corrosion?

A small amount, but I feel that it is lite, and neutralized a year ago.

Quoted from barakandl:

You generally don't want to stick probe leads on XTAL and EXTAL pins of a cpu that is using a cyrstal setup like in this board. The crystal circuit is really sensitive and you will likely stop the oscillation by doing so.
The real story about if the clock is working is the 'E' pin on the CPU. 'E' is the external clock and you can safely probe this. Ideally you want a DMM or scope to check the frequency of the E pin. It should be right at 0.895mhz. VDC reading of 0v or 5v is an indication the cpu or the crystal is not working. The schematic i am looking at is hard to read but I think the 'E' is pin40 of the 6803 chip.
For the RAM chip put a logic probe on the /CS input at P18. When you power up the game it should go high briefly then start pulsing. If it never pulses or reads 0v or 5v always during the power on self test routine i'd check Q6(if always low or 0v), U9, and D6 (if always high but pulse at U9 P6).
U5 U6 and the 6803 must be good too. If you did any soldering work around those chips I'd be double checking it. You should be able to check U5 U6 by pulling the ROMs and PIAs out of the board. Power it up and all address/data go active so then you can check for pulsing on the output sides of U5 and U6.
Make sure the ram chip has power too at P24. Schem shows it P24 of the ram connects to V_AUX which i can't find on the drawing right away. Usually that means it is tied to the reset section... but should read 5v.

First , thanks for your nice reply----
Using a logic probe--- U1(6803cpu) checked pin 40 -- power up- stayed high, no pulsing. Replaced Q6 and D6, no change.
Moving on to NVRAM chip--- P18 goes high at power up, and stays high
Also, you mentioned having 5v @ P24/RAM, I only have 2.45v
I don't seem to have an extra 6803 cpu ic, so ordered a replacement. Am I wrong to believe that this is probably my main issue?

#6 67 days ago
Quoted from mrsodapop:

Also, you mentioned having 5v @ P24/RAM, I only have 2.45v
I don't seem to have an extra 6803 cpu ic, so ordered a replacement. Am I wrong to believe that this is probably my main issue?

VCC of the RAM chip should be 5v. That is problem. What is the voltage on the reset pin of the CPU chip, pin 6? I coudn't location the ram chip's Vcc connection by looking at the schematic, but it is probably from the reset section.

If the CPU P40, external clock, is stuck high and the crystal is good the CPU chip itself is probably bad. Check the reset at cpu chip p6 tho first. If the CPU is stuck in reset the external clock is probably shut down.

#7 66 days ago

Ok, went back and did some checking/rechecking. For some reason I now have 5.8vdc @ NVRAM(U4/P24), other than that no change. Checking CPU pin6 I get 4.9v. CPU pin 40 still stuck high.
Thanks for your help
Aaron

#8 66 days ago
Quoted from mrsodapop:

Ok, went back and did some checking/rechecking. For some reason I now have 5.8vdc @ NVRAM(U4/P24), other than that no change. Checking CPU pin6 I get 4.9v. CPU pin 40 still stuck high.
Thanks for your help
Aaron

*edit*

I found V-AUX on a 6803 schematic. Make sure the 82 ohm resistor at R27 is in spec. 5.8v is a bit much at the NVRAM and R27 drops the 12v down for the RAM.

But if P40 of the 6803 is always high, the reset is high, and you put in a new crystal the 6803 chip itself is likely bad. P40 should be pulsing when the CPU reset pin is high. Try a new known good 6803 CPU chip.

#9 64 days ago
Quoted from barakandl:

*edit*
I found V-AUX on a 6803 schematic. Make sure the 82 ohm resistor at R27 is in spec. 5.8v is a bit much at the NVRAM and R27 drops the 12v down for the RAM.
But if P40 of the 6803 is always high, the reset is high, and you put in a new crystal the 6803 chip itself is likely bad. P40 should be pulsing when the CPU reset pin is high. Try a new known good 6803 CPU chip.

Will check R27, and am waiting for a new CPU from Arcadechips.com. Will report back after it arrives.
Thanks again for your help
Aaron

1 week later
#10 53 days ago

Little to no progress. First checked R27, it was ok, but decided to replace it anyway since it was out-no change. Got 2 new 6803 CPUs, tried them both, but with the exception of pin3(clock signal) on cpu is now 1.2v(was .5v) no change. Went through, and re-checked cpu(U2,U3 eproms/test eprom removed) pins 21-40.

21 5.1v
22 3.4v
23 2.1v
24 2.0v
25-29 2.5v
30-38 4.1v
39 1.1v
40 4.1v
Also reinstalled both game Eproms, and still only get 3 flashes from LED.
That's as far as I got tonight, will go back and recheck other points from previous posts to see if they have changed tomorrow.
Thanks for any insight
Aaron

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