Commodore 64 (C64C) Color (Colour) RAM (SRAM) Repair

A short video covering the repair of a C64C. In the beginning this system would not boot from cartridge, the keyboard was outputting unusual characters to screen and the text was shimmering.
C64 Schematics www.zimmers.net...

[@K1NGARTH3R]

Great video as always :) loved the gameplay at the end, C64 version of GNG as a fantastic soundtrack doesn't it! It looks a pretty good port too!

[@GeoAnas]

Another great one ;-) Thanks for these very usefull videos / tutorial ! Thumb UP !

[@wegi9621]

Indeed. Absolutly.

[@104d_3rr0r_vince]

Amazing job mate!!! You should buy the golden round pin sockets. I have like yours and they are not good enough.

[@markburnett6157]

Very helpful video, recently had some success in removing a duff chips and putting a working ones in. Problem I am having is getting the chips OUT, seems like no matter what I do theres still solder sticking the chips to the boards. How important is flux? I've not used any before but managed to get everything done... still can't work out exactly what is does :-/

[@GadgetUK164]

***** Hi, flux is very important! As is solder wick / braid. I will try and do a video soon on basic soldering and desoldering techniques. The flux when used with desolder braid means the solder floods into the braid very easily. It also helps the solder flow much better when just using a desolder pump.

[@markburnett6157]

GadgetUK164 That would be much appreciated, think I've knackered the last board, trying to change a ram chip, refused to budge so ended up forcing it out... now a new ones in I've got a black screen instead of 427 bytes free...

[@Plan-C]

Nice one mate. Just got back into this with an old c64c off ebay. Good soldering skills, how do you not lift tracks? All the best...

[@GadgetUK164]

The trick is to make sure you use flux, and a good desolder pump. If you make sure the solder has been removed from all the pins properly first, then use a small screw driver to carefully wiggle the pins from one side to the other (they usually make a snap noise when you press the pin one way - provided the solder has been removed properly). Then when all the pins are loose, the chip should just litterally fall off the board. If there's a pin still stuck it will need more solder and flux before you attempt to desolder it and remove the solder again with the desoldering pump. Sometimes heating a pin for several seconds (or more) can make all the difference, as the heat then has time to spread properly and make the solder on the opposite side molten. It's all about taking your time, and practice! Thanks for watching and commenting =) Let me know how you get on with your C64C =)

[@GadgetUK164]

use desolder braid (and flux) to get the solder off the legs afterwards. Then use pliers to make the pins totally straight. Some times you can just rub the soldering iron over the pins to get rid of small solder points etc.

[@RetroMarkyRM]

nice fix mate. ..sometimes "gut feeling" comes to fruition :)

[@GadgetUK164]

Very true!

[@Beaps73]

Wow I would love one of them diagnostic carts mate, did you make it yourself?

[@GadgetUK164]

I just used the Easy Flash cart and programmed that with the C64 diagnostic image. You could make one relatively easily though if you can buy a 16Kb cart PCB, or make one.

[@colinellett]

Hi, I and worried that one of the chips in my C64 may be dying. It's not quite the same thing as this video as the colours and picture are fine. However, I have random pixels that flicker. They seem to just be in certain games and always in the same place. They don't flicker in Vice, so I am thinking something is on the way out. Have you come across this? (they are all over the place in the 'DELTA' title screen)

[@GadgetUK164]

+Colin Ellett My first though is perhaps the colour RAM or PLA is on its way out, but it's most likely a bad connection on the VIC chip (I had the exact same problem with mine). Do you have the version where the VIC chip has no heat sink? Try removing the VIC (carefully, using a screw driver on each side - inbetween the chip and the socket, once removed carefully line it back up with the socket and re-seat it), and then re-test. If that fixes it I would suggest putting some heat sinks on top of the VIC. Mine did exactly that, and after a week or two after re-seating it the same problem occured. I ended up cleaning up the pins on the VIC chip and after fitting heat sinks it hasn't re-occurred.

[@colinellett]

+GadgetUK164 I have a 1983 model (250407) where there is a metal box surrounding the VIC-II and which acts as a heat sink. I removed the VIC-II and re-seated it. Made no difference. I tried putting in a new turned pin socket, but that made no difference either. Do you think the VIC-II may be bad?. I can do a video of the problem if it will help... (really appreciate your help, I love your vids!)

[@GadgetUK164]

It's possible its the VIC-II, I have got another VIC-II chip that does strange things with graphics. A video might help!

[@colinellett]

+Colin Ellett Hi, you're probably bored with this now, but just in case you're not: I ran a Commodore 64 Diagnostic cartridge to test the system (including the adapters for ports etc) and it tells me that U1 is bad (keyboard + Joystick). The strange thing is, I swapped U1 & U2 and it still fails on U1? Puzzled

[@colinellett]

+Colin Ellett bad connection with the keyboard tester, now passes fine. Diagnostics pass everything. I guess it must be the VIC-II after all...

[@MaCJaX88]

Love the videos !! Helped me out a lot !! Thank you !!! Was having the same issue and replace the PLA chip. Turned out the PLA chip was fine. Now I am looking to replace this chip. Any chance you have a part number for the color RAM ? I can only find the chips on eBay for the older brown Commodores. Thanks !!

[@GadgetUK164]

You just need a 2114 (there are 5 or 6 equivalent parts) - store.retroleum.co.uk/c64-chips or www.ebay.co.uk/itm/NEC-uPD2114LC-2-SRAM-1024x4-bit-/162503484200?hash=item25d5f66328:g:u~UAAOSwzaJX7OhA

[@GadgetUK164]

The colour RAM on the 64C is the same as the breadbin btw!

[@00Skyfox]

Good work! Recently when scrapping some old circuit boards I got very lucky in that one thing was loaded with M2114 chips, the same chip the C64 uses for color RAM. That was fortunate because I had no backups, as my only current C64 board used for salvage parts had the color RAM chip destroyed when I was trying to remove it.

[@angerboitoo]

Thank you for these C64 vids. I have a handfull C64s myself, and I'm eager to see if I can get a couple of them up and running. Where can one obtain such a diagnostic cartridge?

[@WKsiliconite]

I just recently picked up two C64s on ebay. The first one had scrambled up text, then nothing. I got the second one and it is working ok,the blue is all one color, I messed with the knobs next to the VIC, and it's something else. Now back to the first, I swapped the MPU and I get a constant picture,but the text is scrambled but a pretty blue border. I tried all the other chips, socketed ones--CIAs, PLA,SID,the 3-BAsic, Kernal, and Character, all the same on the 1st, and 2nd. The first is a 83, and 2nd is a 82. I love them, but I'm waiting on my Dead Test cart. Any ideas on the (true Blue) one, lol?

[@brooknet]

I like your soldering skills. I have trouble with my desoldering braid too: it dries out. I find that applying a bit of rosin core flux fixes it.

[@GadgetUK164]

Thanks =D Yes, flux really helps with desolder braid.

[@RETRONuts]

Hi Are you a member of the Lemon 64 forum,Iam from there and thanks for a great video,you can learn a lot watching your videos.I have a problem with mine its the cpu I think,using the test crt in Easy Flash and it crashes at RAM TEST 1 and stops,oh and I don't have that chip on my C64C board..?

[@GadgetUK164]

+Spanner Nick I don't really hang around the Lemon 64 forum much these days! If your system is crashing on RAM TEST 1 it sounds like a main RAM problem (not video RAM). There will be 2 x 4464 DRAM chips on there, sounds like one (or both) are faulty.

[@RETRONuts]

+GadgetUK164 Thanks for the reply,how long have you been fixing c64,do you fix Atart 520s too,I remember working in a computer shop upgrading them to 1040..:),Its the first time I have seen a Rev 4 board mine are a rev A and B,B is the one with the problem,all because the wire touched on the tape deck connector.Oh thanks for the Easy Flash Video,Now I have one cos of that..;)

[@johnandrews2167]

Great repair! Say, would you know if that diagnostic cartridge may be available as a program that can also be run from a disk? Also, I understand there is a cable to use with that cartridge? Please tell about that. Thanks.

[@GadgetUK164]

There probably is diagnostics software you can run from disk but I've never used it. A diagnostics cart or 'dead test' cart on eBay will set you back around £15 to £20, so I would recommend getting one. The problem with disk is for some faults you cannot get the program to load. The diagnostics carts tend to be better written, so testing RAM and CIAs works more reliably than if you were to attempt to load from disk or tape.

[@GadgetUK164]

The cable set is optional - they are used to test the ports on the C64, but generally they aren't actually required as you can test them other ways - eg. load a game, test the joystick ports. Load a disk which will test one of the CIAs. Press each key on the keyboard and you've tested the other CIA, etc. etc.

[@wegi9621]

Fortunatelly in my C64C the PLA SHARP is hard to killing bcos till now doesn't have substitute. Lucky man :) Btw great job.

[@GadgetUK164]

Is your sharp PLA faulty? I've not come across a faulty PLA on a C64C before! It's frustrating because the original PLA was easier to replace with modern substitutes etc, the C64C PLA is shrink DIP or PDIP I think and because there's more than just the PLA in there (other common logic merged into it), it's more than a PLA =/

[@wegi9621]

No no its ok. But iti have colour RAM inside, that way we deosn,t have substitute :)

[@dylanbobek3158]

I’m having an issue with my c64 when I turn it on it shows the basic screen but instead of basic it shows a bunch of random letters and numbers but if I let the unit warm up and then turn it off and then on it works fine I want to diagnose the problem but I can’t find that cart you use any where

[@GadgetUK164]

There are a couple of possibilities, it could be a bad character rom chip, bad PLA or VIC. The most often cause for this that I've seen is the VIC making a bad connection to the socket. You could try reseating the VIC chip - perhaps clean up the pins on the chip first, and consider using deoxit or similar in the socket.

[@GadgetUK164]

With regards to the cart I use - its just a diagnostics cart! Search on eBay for C64 diag cart or C64 dead test cart - you will find loads for sale.

[@HuntersMoon78]

I'd be a happy man if I had your kind of knowledge and soldering skills

[@GadgetUK164]

Old video this! Quite embarassing to watch back now lol. I was just getting back into repairs towards the start of my channel so I was unconfident and had forgotten what I once knew etc. Hopefully it's clear as time has gone on I got more up to speed with these C64 repairs.

[@HuntersMoon78]

@@GadgetUK164 Yeah I know it's old but these video's keep popping up in my recommended video's so I watch them. They are super interesting to me.

[@GadgetUK164]

Thanks =D

[@craiggilchrist4223]

Really wish i had your knowledge mate. Fixed a few things by watching your vids which is good. I just dont know how to diagnose problems. Just self teaching really. Got consoles and computers dating back to the late 70's that need fixing i just dont have the knowledge. Could do with having my firmware upgraded matrix style. Wow i know electronics. lol Keep up the good work mate. Respect! Just quickly, could you do a vid on how to read schematics in a logical fashion?

[@GadgetUK164]

craig gilchrist Thanks for the nice comments and feedback =) I will do some tutorial type videos soon, just to explain some of the basics and how some of these old systems hang together etc. It's just finding the time! Like anything though, the more you push yourself into things you don't understand the easier it becomes, and soon you can diagnose faults on things you've never even seen before.

[@craiggilchrist4223]

Nice one, yeah finding time is the problem. Nothing like the satisfaction of bringing something back to life. I always think the amount of electronics that people throw away and may just be a bad cap or something simple.

[@NotHimJim]

BBBoooom!! Another one fixed. Top stuff!

[@GadgetUK164]

Thanks lol! There's 3 or 4 more C64 repairs to come yet lol. One compressing at the moment. Know anyone that wants a C64? I've got them coming out my ears at the moment lol.

[@NotHimJim]

Nobody wants C64's!! Spectrums are where it's at mate!! ha ha. ;)

[@GadgetUK164]

Hahaha! I am hoping to get a +2 or +3 at some point!