Commodore 64 can't boot up, Is this mean 6510 failed?

[wellswang]

Hi,

My C64 boot up with wrong character and with garbage message on the screen.



I use Diag Test Cart to diagnose it, it says "NGZERO 0002E02". Because Zero Page memory is internal to the 6510, does it mean 6510 MPU is failed?
I tried replaced all 4164 RAM chips, but it didn't change anything.
If 6510 is failed I should buy one to fix it. It's diffcult to get a 6510 now.



Thanks!

BR,
Wells.

 

[Ruud]

If the 6510 failed, there was hardly any chance you would get a screen at all. And the 6510 has no internal memory except some registers. If the error is Zero Page memory, then start checking the RAM.

 

[atariquest]

The DIAG CART is an invaluable tool to help identify hardware failures, but it only tells you where a failure is found, not the root causes for the error. What you are seeing on the screen is obviously not normal behavior for the DIAG CART. Therefore, the output may not be very helpful. For example, the CART should read "ZERO PAGE BAD" to indicate that error. Instead, you are seeing garbage on the screen. In other words, you are not seeing reliable output.
Since you have already changed the RAM, I would check out the 74LS series chips like U14 next. These can prevent RAM from working correctly and will never be identified by a testing cartridge.
Do you have a DEAD TEST CART as well? If you get a RAM error from the DEAD TEST then the chance of a logic IC causing the issue is high because you have already swapped RAM.

Marvin

 

[wellswang]

Thanks!
I will test it this weekend.

 

[wellswang]

If the 6510 failed, there was hardly any chance you would get a screen at all. And the 6510 has no internal memory except some registers. If the error is Zero Page memory, then start checking the RAM.

Hi Ruud,

Thanks, but in C64_Diagnostic_Instruction_and_Troubleshooting_Manual_(326070-01), it says Zero Page Bad means U7 6510 failed. I also think if 6510 failed, I can't get the blue screen, maybe it's wrong.


Thanks, I will check it carefully this weekend.

 

[daver2]

The highlighted area is not consistent with the datasheets for the 6510.

I/O registers 0 and 1 are stored in page 0 - but I don't see any onboard RAM though.

Dave

 

[ClassicHasClass]

Correct. Only $0 and $1 are internal to the 6510; the rest of zero page is regular RAM. All that document proves is that Commodore's quality assurance at the time was as bad for their documentation as it was for their hardware.

 

[grimm]

I would suspect the PLA before anything else, especially if you have replaced the ram. The diagnostics cart replaces the ROMs but it can't replace the PLA. If it's not the PLA then start looking at the logic chips. There are several reasonably priced modern PLA replacements that work well (GAL PLA, Plankton, etc.)

 

[giobbi]

A little OT about the 6510 scarcity: on github there's a project for an adapter that replaces 6510 and the 264 series CPUs with a 6502. It's a little bit tricky because of the small smd components, but it works like a charm on my C=64.

 

[wellswang]

I checked all RAM related circuits, resolder all RAM IC sockets, but still got garbage characters on the screen.



Then I desoldered U7-6510, U17-PLA, U18-SID, U6-2114(color RAM) and tested them on another NTSC C64, they all works fine!
I also desoldered U13/U25-74LS257, U14-74LS258, U8-74LS06, U30-74LS193 and tested them on my logical tester, they all works normal.
U31-74LS629 is replaced recently, the clock signal is normal now.
So these IC shold be ok now.




When I use dead test cart, I got this screen, although the screen is like chaos, but the test seems running, I can hear the tone from sound test sucessfully.



When I use Diag Test Cart, I got this result.


I really don't know how to diagnose it. It's so strange, can any body help me?
Thanks and wish you have a nice weekend!


BR,
Wells.

 

[giobbi]

Take a look at this pictures and see if some of them is similar to your problem (look at the C64 series first).
https://portcommodore.com/rcarlsen/cbm/misc/pict-o-guide/

 

[wellswang]

Finally, I found the problem!
I checked the circuits again, against the schematic.
Line by line, trace by trace.
After hours work, I found that the trace between U13 Pin4 and U14 Pin4 was broken!

I fixed it. Now the C64 is back to life!!!
Thanks for your kindly help!





BR,
Wells.

 

[Brian Todd]

Well done ... labour of love

 

[daver2]

I must admit I was going to suggest a RAM address fault; but, given the fault you found, I am surprised the machine even worked at all!

Dave

 

[giobbi]

Well done! Proof of patience... something that only married people have LOL