C64 Strange Text issues

[fitzsteve]

Howdy All,

I got a C64 today which is exhibiting some strange issues; seems partially working, at least I can boot some games from my easyflash but text is garbled up and some load, some don't.

Any C64 experts here able to offer some advice to a solution? The unit it's self needs a good clean but I've wiped it over and cleaned the connectors on the back, blown the dust off the keys with a can of compressed air, that's all (not opened it yet)

There's a missing cursor key but I'm sure that's not the issue



Thanks in advance.

 

[Junior]

Porbably a Bad U6 (Color RAM) .

take a look at this site very helpful http://derbian.webs.com/c64diag/index.htm

 

[fitzsteve]

Porbably a Bad U6 (Color RAM) .

take a look at this site very helpful http://derbian.webs.com/c64diag/index.htm

Thanks I will check it out!

 

[Paradroid90]

Howdy All,

I got a C64 today which is exhibiting some strange issues; seems partially working, at least I can boot some games from my easyflash but text is garbled up and some load, some don't.

Any C64 experts here able to offer some advice to a solution? The unit it's self needs a good clean but I've wiped it over and cleaned the connectors on the back, blown the dust off the keys with a can of compressed air, that's all (not opened it yet)

There's a missing cursor key but I'm sure that's not the issue

View attachment 133180View attachment 133184View attachment 133185View attachment 133186View attachment 133183View attachment 133182View attachment 133181

Thanks in advance.

Hi Steve if you need a spare cursor key I might have one in my spares. Agree with Junior looks like the color ram

 

[fitzsteve]

Hi Steve if you need a spare cursor key I might have one in my spares. Agree with Junior looks like the color ram

Hey nice to read you mate, will have to meet up soon. You coming to Towcester?

How easy is the Ram to do? I've got a PM out to Bas regarding Jiffy Dos so maybe it's something he could do for me? If you have a spare cursor key that would rock.

Cheers.

 

[timharris]

replacing color ram is relatively easy with the right tools.. can be a tad bit time consuming if you are doing it as a one off manually but can be done.

if you want to do it manually the cheapest way;

- soldering iron that delivers enough heat (the low wattage ones won't be able to get enough heat in since the c64 soaks it up on ground areas)
- a roll of wick (to absorb tin)
- a bit of solder (re-soldering a blob can make it easier to remove the old solder)
- some flux (a simple flux pen will do to make the tin flow easier)
- small flathead screwdriver (to wiggle pins that you de-soldered to see if they move / carefully pry the chip up after resoldering)
- solder sucker
- and of course a replacement chip

most items on the list (except for iron and replacement chip) are very cheap.

optional:
- a socket so you that if needed you can remove/replace a chip next time without resoldering

in short..

- add flux to current pins
- add some new solder to the pins so it mixes with the old
- heat pin and use the sucker (sometimes wick will help too)
- give pin a little push left/right with screwdriver.. can you move it ? not .. resolder and try again
- can you move it? great.. move to the next pin and do so for all pins

- flip the board to top side and at this point you should be able to lift the chip or at least move it around.

note -> although some force is needed sometimes to remove a chip, too much force and you will rip a trace out of the mainboard.
that can be fixed with additional wires most of the times.. I guess use controlled force would be the best way to describe it

- have a looksee if some residue solder on top side is still clinging to the board.. if needed add a bit of flux and fresh solder on that point,
and use wick to remove it.

 

[roy_bates]

i think its the kernal rom,is it a -02 on the end?

EDIT: nah,i dont think it is now,looked at the other pictures,although im not sure if its the colour ram myself

 

[TheCorfiot]

You have either a PLA issue or the Character Generator ROM is playing up.. Regardless my friend, If you are sending it over for the upgrade then I will sort this out for you at the same time.

Bas

 

[Paradroid90]

Hi Steve if you need a spare cursor key I might have one in my spares. Agree with Junior looks like the color ram

Hey nice to read you mate, will have to meet up soon. You coming to Towcester?

How easy is the Ram to do? I've got a PM out to Bas regarding Jiffy Dos so maybe it's something he could do for me? If you have a spare cursor key that would rock.

Cheers.

Good to here from your to my friend. As you have already PM'ed TC then whether it is the color ram, PLA it looks a simple fix whatever it is. Yep should be up at Towcester, but flying back from Rome on Friday morning so going to be tight for Saturday. Let me know if you need the key. If the key plunger is buggered I should have a spare one of those. I can drop it in the post. Lets make this 64 whole again

 

[stephenfalken]

I once had a similar issue with the garbled BASIC text with some characters in the correct place and others not. Eventually I managed to narrow it down to being an address line jammed, caused by a bad desolder job on the board. Once I corrected this with a jumper wire it worked 100% perfect. I suspect your issue is something similar or as previously said, a bad PLA or RAM chip. Never seen the colour RAM cause this.
Good luck!

 

[fitzsteve]

Thanks for the replies all, sent this off to Bas yesterday so fingers crossed

 

[fitzsteve]

Hi All, Little update, Bas worked his wonders on this fine machine and I now have it back and working

Here's a quote of Bas' findings:

The Culprit was the SN74LS373 which gave RAM access to the VIC II. The Computer side worked fine but the VIC couldn't access the RAM correctly to display the Screen

I've also replaced the entire keyboard switch and put a new CSR key in for you too. All keyboard contacts cleaned and verified.
To make life easier for the future. I have socketed your PLA, SID, CPU, Both 6526 CIAs and ROMS so its easier for you to just swap out failed chips.

Also Jiffy Dos installed with toggle switch.

And some pics...




Can't thank you enough Bas

 

[TheCorfiot]

Absolute Pleasure Steve