Faulty C64 advice

[fitzsteve]

Hi all, my C64 has a bunch of messed up text, does anyone know what might be the culprit?

Chips are socketed so hopefully an easy fix!

Ta in advance

 

[miggymad]

Suspect either the character or kernal ROM has decided to shuffle off to silicon heaven

 

[fitzsteve]

Thanks, I'll have a look see if I can find these chips, it had jiffy dos installed, did that replace the kernel?

 

[miggymad]

Thanks, I'll have a look see if I can find these chips, it had jiffy dos installed, did that replace the kernel?

Yep, it's a one-for-one swap

 

[fitzsteve]

Cheers I'll see if I can get a character Rom and if it's not that I'll have to get the Jiffy Dos again!

 

[miggymad]

The character ROM should have MOS 901225-01 or similar printed on the chip.

 

[Sardine]

adrians digital basement, Jan Beta, the retro channel and Mr Lurch's Things are some good sources for C64 repairs,

Adrian has done quite a few and one of his i remember a very similar fault to yours.


from another forum and adrians info about incorrect characters miss-spelling etc.

popeye2755 wrote:One thing I would do, is to replace U13 and U25 (MOS 7708) with a generic 74LS257. I repair a lot of 64s, and the failure rate of MOS devices is high. I replace them automatically.

Yes, you nailed it! Replaced them with 74HCT257 and, boom, problem gone!

Thanks a ton for your help!

 

[fitzsteve]

Cheers for the info!

 

[fitzsteve]

Small update, it's not the Character Rom, the VIC or PLA (have tested chips from a known working C64) one of the logic ICs is socketed from a previous repair so have ordered a replacement, fingers crossed.

U13/U25 are soldered so would need desoldering. Something to try next I guess! (If U14 doesn't resolve)

 

[Sardine]

Mostly the reason why I'm too scared to plug in my C64 breadbin, never mind the space to also set it up with my 1541 and a monitor

I've got a boxed C64C and for some reason they seem bomb proof compared to the "don't look at me or ill break" Breadbin.