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CPS-1 A Board (DASH/12mhz) - Color Palette Issues

YesAffinity

YesAffinity

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I think "color palette issues" is the best description of the problem. Hoping for some help on where to start probing next.

The CPS-A-01 custom is known good. Confirmed that the issue is specific to the 'A' board. Found 4 VRAM chips that were mis-behaving (6L, 6N, 7L and 7N), and replaced them with no improvement. Confirmed they are now behaving like a working board's chips in those same locations. What next?

See video below, of the issue.

 
We need more information: you say CPS-A-01 is known good. Was it swapped with an other board? What was the misbehaviour of the 4 faulty VRAM? How did you come to the conclusion they were bad? Replacing them didn't fix the colour issue but did it clear an other graphic fault?

Following what you said I'd jump directly to the palette RAM chips @2D/3D/4D/5D and probe around.
 
Thanks, apocalypse. CPS-A-01 was pulled from this board and replaced with a NOS chip. Symptoms did not improve or change in any way. The pulled CPS-A-01 was used to repair another board. By inference, this A-01 is good.

The faulty vram chips had pins 4, 5 and 9 stuck high. SIO pins which are normally floating. Probably of no consequence truly, but if that problem existed, there could be other problems with those chips.

Out of 2D/3D/4D/5D, I only find 5D and it is an LS07. I'm probably being dense, but where am I looking for these chips?

(click through for full res and/or download the image)
 
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YesAffinity said:
Thanks, apocalypse. CPS-A-01 was pulled from this board and replaced with a NOS chip. Symptoms did not improve or change in any way. The pulled CPS-A-01 was used to repair another board. By inference, this A-01 is good.
Click to expand...
That is very good for you, it means your board is definitely fixable since all other parts can be replaced.
YesAffinity said:
The faulty vram chips had pins 4, 5 and 9 stuck high. SIO pins which are normally floating. Probably of no consequence truly, but if that problem existed, there could be other problems with those chips.
Click to expand...
Thanks for the precision, I understand. They probably started to develop some internal failure and it was wise to replace them.
YesAffinity said:
Out of 2D/3D/4D/5D, I only find 5D and it is an LS07. I'm probably being dense, but where am I looking for these chips?


(click through for full res and/or download the image)
Click to expand...
Sorry that's the positions for long A-boards.
I'll have a look later and give you the correct locations.
BTW it seems you need a KLOV account to open the picture.
 
thanks guys. Sorry @ack, i didnt see your post either.

I was speculating C2 and C3 were where to focus, thank you both for confirming. Will poke at those this evening and report back.

Sorry the picture requires login. Not sure why thats happening, as I posted it publicly. Will see if I can figure that out too. :/
 
Okay, I believe the link in post #4 is good now - no login required.

I probed the (2) M5M5178P's at 3C, and found no problems with them. They behave identical to a working board. Note 3C seems to be the location for both chips. 4C and 4E are LS273's, just below the lower M5M.

I'm guessing the next thing to check is 273's and 367s?



Seems my cables allowing me to separate boards and probe the component side, are acting up. I'm stuck in a boot loop with them. Ordered some more cables, but might be a couple days before I can proceed further.

Oh, and sound died while I was probing the M5M's. Hung on a note of the attract mode music, and dead on power cycle. Amp pins are all stuck low or high, as are other components in the audio circuit. ;( More repair fun added to the docket. :cursing: :P
 
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Yes probe outputs of the 273s and 367s for any stuck signal.

For the sound, as usual, starts with the basics: reset signal and clock on the Z80, activity on busses, etc.
Z80s are overclocked on CPS1 and tend to die prematurely.
 
Well, life has been hectic, as I'm sure it is for all of you. Hope everyone is staying healthy and safe.

I have been stabbing at checking all major components, from the RAM at 3C, out to the RA outputs. I have found nothing acting up or acting differently than a known good A board.

I went back and checked all the RAM at locations 1-7 and 9-11, as well as the LS's at 10L-10P, and LS's at 1F, 3F and 4F. Everything looks good from the probe's perspective.

Suggestions on where to go next? Time to start scoping? Thanks all for helping me take my troubleshooting to the next level (for me).

In good news, sound came back and seems to be performing normally. ?( ^^
 
I would look at the color bars in the test menu so see if it provides any more insight. If only 1 or 2 of the rgb colors are bad it should narrow down the issue.

I somewhat still lean to it being the palette ram. Even though you see pulsing on all the lines there is no way to know if data is being stored/retrieved properly with a logic probe. For stuff like this I use a neoloch sram tester or before I had that a neogeo mv1 board with a bunch of zif sockets for swapping/testing ram/z80/etc.
 
I went ahead and shotgun replaced the RAM chips off a parts board. I don't know that the donors from the parts board are okay, but there was no improvement with the replacement chips in place.

@ack Looks like I need to add a tool to my tool belt as well. Seems the Inquisitor is no longer available in the US, and out of stock at Pinball Classics, who took over the rights to it. Any other comparable devices at a comparable price point that you could recommend for ram testing?

:edit: oh, and here's the test menu color bar. The whole right half of the bars are washed out with green.
 

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This is getting a little out of my wheel house as I mainly deal with fixing multi-slot neo geo boards, but have been teaching myself cps1 boards as of a month ago.

The pic gives the impression that green is over saturated over the entire screen. Based on the schematics I think you should check RA6-RA11 for correct resistances. This is what I see for all those on one of my boards, testing from pin 1 on each

pin 2 = 0.1k
pin 3 = 0.22k
pin 4 = 0.47k
pin 5 = 1k
pin 6 = 2.2k
pin 7 = 4.7k

My guess being one or more of the RA's for green could have incorrect or shorted pins to pin 1 causing the excessive green.

I don't have any other suggestions for a memory tester. I've been satisfied with the neoloch one so haven't looked for anything else. I was actually hoping he was going to open source it since he shutdown, but guess not. Wonder how much the pinball folks had to pay.
 
@ack thanks for those readings from your board and guidance. I will check those.

To confirm- those were measurements taken in circuit and with the board powered and fully operational (a+b+c boards all running together and game 'playing')?
 
Finally fixed this. What is missing in the snippet of the schematic above, and what I'd been overlooking are LS245's 5F and 5G. They are on the schematic, just below what I snipped.

Probed them, found 5F pin 11 making odd noises. Checked 4E pin 18, and it's pulsing normally. Powered off, checked continuity, and there wasn't any. Checked on a known good board, and there sure should be. Through on a test jumper, and got glorious normal operation.

I, in fact, fixed (4) CPS 1 A boards today, the other 3 all with audio issues. All had floating pins requiring jumpers, one also required a replacement SOU1 PAL.

Next, I'm on to a 10mhz A board that is seemingly dead - no video and no playing blind. I checked the 16mhz and 10mhz oscillators, and they are pulsing. Any suggestions on where to focus next?
 

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Thanks @Raph_friend. I checked the 68k, and its halt and reset is operating normally. The CPS-A-01 RESETB, BRB and CK250 are (possibly stuck) low. On a normally operating board, RESETB and CK250 are high, and BRB is pulsing. If I'm reading things correctly, these are all outputs to 8D. Am I reading things correctly? And, is this indication that CPS-A-01 is dead?

Interestingly, when I was probing 8D, shorted a couple of its pins, and the blanka stage music started playing. That is the only sign of life, video or audio, that I've had from this board yet.
 
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