Troubleshooting a C64: Only print "READY" at power-up (missing other startup lines)

[mvancopp]

Hi Everyone,

I am new to the C64 community and have a C64 I recently came into my possession that prints "READY" at power-up but does not print the first line, "COMMODORE BASIC V2", or the second line stating the memory. Once READY is displayed I can type, such as "10 PRINT T" and press enter the screen clears and never returns. This C64 is a very early model with the 5 pin DIN video connector (a 326298 REV A motherboard).

Does anyone have some pointers on where to start troubleshooting? Any suggestions are appreciated.

 

EDIT:

The first two lines are printed but disappear to quickly to completely read. I see some of the text flash quickly, like COMMODORE or BASIC, but are replaced by the READY and the rest of the screen appear as spaces. 

 

Thank you,

Mark

 

Edited December 23, 2022 by mvancopp

[carlsson]

It might be partial bit rot on the BASIC ROM if it prints the message, hits an invalid break instruction and triggers an interrupt.

[hofster]

10 hours ago, mvancopp said:

Hi Everyone,

I am new to the C64 community and have a C64 I recently came into my possession that prints "READY" at power-up but does not print the first line, "COMMODORE BASIC V2", or the second line stating the memory. Once READY is displayed I can type, such as "10 PRINT T" and press enter the screen clears and never returns. This C64 is a very early model with the 5 pin DIN video connector (a 326298 REV A motherboard).

Does anyone have some pointers on where to start troubleshooting? Any suggestions are appreciated.

 

EDIT:

The first two lines are printed but disappear to quickly to completely read. I see some of the text flash quickly, like COMMODORE or BASIC, but are replaced by the READY and the rest of the screen appear as spaces. 

 

Thank you,

Mark

 

Could be a memory problem too or maybe PLA but the PLA was not as likely to fail on the early boards as it is on the later longboards.

A diagnostic cartridge like the 586220 would be helpful. The Dead Test diagnostic cartridge (781220) might be helpful too if the other one refuses to run.

 

Are any chips in sockets?

 

[+OLD CS1]

When the header pops up for the split second, do you happen to catch how much memory it says is available?  ISTR this is also a symptom of bad RAM.

[mvancopp]

Thanks @carlsson, @hofster, and @OLD CS1 for the suggestions.

The symptom changed over the period of a few hours. The "READY" display began to become intermittant. It flipped between the too fast to read lines and the READY and a the screen just being the blue on light blue screen with no characters. A few times it displayed some jumbled texted instead of the READY word. Now it is always te blue-on-light blue empty screen. Sometimes things just go down hill... 😏

I swapped out the Character ROM since it is in socket and I have, and can burn, 2532 eproms. There was no change in the behavoir.

@hofster, chips in socket: 6510, VICII, PLA, CHAR ROM, and SID (SID is not installed for any of these tests).

The DRAM chips are the gold colored top chips but I need to desolder them to test. On the list to do. The memory mux chips of not MOS chips, I read those are prone to failure. I do not have an alternate PLA, VICII, or 6510, but I do have a PLA replacement (the two 20v8 version) and a dead test/diag cart on order. I cannot presently make 2564s, nor do I have an adapter but I can make one for testing the BASIC and Kernal ROMS (would need to desolder and socket these). Just need to find the time, hopefully this coming week.

It soundslike RAM is #1 suspect and then BASIC ROM, followed by PLA? Does that sound like a reasonable plan?

 

Thanks for all the suggestions. This troubleshooting will at least make me familiar with the C64 hardware. 🙂 

[mvancopp]

Sorry @OLD CS1, I missed answering your RAM size question. No I couldn't read the free RAM in the flashing of the first two lines. It was too fast to focus on before it disappeared.

 

 

[carlsson]

With the added symptoms, I agree it sounds more like a PLA issue than ROM issue. If you have any game cartridge, it should not utilize BASIC so it could rule out that one if the cartridge also fails.

[hofster]

On 12/24/2022 at 1:34 AM, mvancopp said:

 

@hofster, chips in socket: 6510, VICII, PLA, CHAR ROM, and SID (SID is not installed for any of these tests).

Sorry for the lack of response. My notifications aren't working.

I was thinking that there might be some chips that could be removed for testing purposes but it's only the SID and Char ROM in your case then and you already ruled those out.

The dead test cartridge is a good thing to try. If the dead test passes without errors it's likely a ROM problem.

[mvancopp]

Hi All,

I had some time so I took a look at this. First using a two-channel scope I looked at the RAM. When the RAM is selected, read or writes, the data lines were always driven and changing levels. So likely not a RAM problem. Next was the ROMs and the Character ROM was already confirmed by the output of the messages, so I tried the BASIC rom. I desoldered it, installed a round-hole socket. I then read the ROM and the checksum did not match the downloaded binary. I built a 2364-to-2764 adapter, programmed a 2764 from the downloaded binaries and viola up she came! 🙂

I also found a heat sink was missing from the 7805 by the joystick ports. This manifested itself after warm-up as strange lockups, video issues, and general instability. Installed a nice heatsink I had from another project long ago and all those issues stopped.

 

Thank you @hofster, @carlsson, and @OLD CS1 for your input and advice. It made the troubleshooting much easier and faster.