c64 repair or replace? (Solved)

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c64 repair or replace? (Solved)

Postby Joseph on Wed Jul 02, 2014 10:39 am

I got my childhood c64 out of storage found most of it minus serial cable and monitor cable. So I checked out the power supplies for the 1541-II and C64 both tested ok, under loaded conditions... I don't have a scope so can't tell how much ripple is on the line.
Plugged it in and no light come on, did some power checks and found the din connector had dry solder joints and the power switch was faulty, so re soldered the din connector and cleaned the switch contacts.
Try again, light come on and black screen. Bugger, check for hot chips, none seem hot, the VIC and SID are warm to the touch.
Now the strange part, if I connect the datasette and press any button (rew, fwd, play) then turn on C64 it works, I can even load games from tape and play them just fine, when stop is pressed (on datasette) the computer crashes immediately. I have also noted that the datasette dose stop and start as normal during loading and game play. It seems there must only be a minor fault with this machine I would like to fix it or find someone who can. Or should I battle it out on trademe? Any advice greatly appreciated, I have purchased another power supply and serial cable so will try that when it arrives. In the meantime I am going to make a video cable for my C1802,
Last edited by Joseph on Tue Jul 29, 2014 8:54 pm, edited 1 time in total.
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Re: c64 repair or replace?

Postby Joseph on Fri Jul 04, 2014 1:03 pm

An update on my poor C64...
It would appear that the MPU has partially failed
I have bridged the datasette transport switch which has made my c64 usable, If i remove the short the computer crashes immediately (unsure why, it has little to no effect on board voltages).
I have only a few programs on tape so still looking for a serial cable, I had forgotten how challenging these games are.
Have now made a video cable to connect my c1802 monitor, was much easier than I had thought, I may end up making my own serial cable if I can locate the correct din plugs...
So I now have a working C64 ready to help relive my childhood, and maybe a little programming if I can remember commodore basic & machine code.
With the sort in the system seems stable and ran for about 8 hours straight during a night of waiting for tapes to load and clicking joysticks!!!
Are there any nos chips available, if so who do I contact?
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Re: c64 repair or replace?

Postby tezza on Fri Jul 04, 2014 7:48 pm

Sounds like progress Joesph,

I'm not sure about C64 chips. There are plenty of beaten up units around though. It shouldn't be too hard to find a replacement C64 board.

That computer is not my specialty. Our Commodore enthusiasts are a little quiet on the board at the moment..
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Re: c64 repair or replace?

Postby RonTurner on Fri Jul 04, 2014 9:42 pm

I made up an online audruino c64drive emulator project so I can assemble c64 assembler progs straight onto a disk image then just type the line of code to load and run the file. I tried it with a few demo programs I Google's, pretty good setup for demo coding but a bit bulky because a laptop is attached, I just have mine setup like that so code can be instantly set to the real commodore.

C64 prog studio.

I started translating a four direction tile scroller from another assembler but it couldn't get vertical scrolling to work smoothly, its pretty cool when you can do all the text editing on a modern computer and assemble it on a modern setup. There is some great hardware in the c64 to play around with like hardware scrolling and sprites.

Lemon64 is a very active forum when it comes to tech support. I bet you get an answer after a couple of hours, they really love there commodore's
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Re: c64 repair or replace?

Postby Joseph on Mon Jul 07, 2014 11:51 am

Hi thanks for your advice, Lemon64 were certainly helpful, The general opinion is that the MPU has failed most likely due to a short at the datasette port probably caused by the sad state of the internals... (bugs dirt damp etc) I powered the system up before stripping and cleaning, Lesson learned the hard way.
I have been contacted through lemon 64 from a chap in the UK who can supply an MPU (both options available)
has anyone purchased items from Ian Gledhill in the UK? dose he have a good reputation? Have been burned with overseas purchases before, just a little cautious.
I have learned a lot during testing of this computer, and discovered its not the black art I had assumed.
Ron sounds like you are light years ahead of where my programming skills are I'm still experimenting with sound and sprites, I was not aware the the C64 had hardware scrolling, will be the next thing to learn about, My experience has all been on actual equipment, I have not tried to interface my C64 to my PC, but looking at making a cable to connect my 1541-II to my PC its an early celeron and has the old style parallel port, so the cable should be fairly simple. I have found the C64 emulation software frustrating, as I keep pushing the wrong keys!!!!
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Re: c64 repair or replace?

Postby SpidersWeb on Mon Jul 07, 2014 2:33 pm

I built myself the simple version of one of those cables. If you have the option to build or buy one of the faster/fancier ones - do it - writing disk images with the basic cable I made was painfully slow.
I eventually just went and did something else for a while.

JayCar stock the DIN connectors etc - I found the best way was to fill the inside of each pin with solder and tin the wire. Then heat the end of the pin and slide the wire in. Was a little bit fiddly. I also found to help with heat on the plug, and hold it in place, you can stab the other end in to a potato.
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Re: c64 repair or replace?

Postby RonTurner on Mon Jul 07, 2014 6:07 pm

I found jcars din sockets just a little cheap and nasty ;-)
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Re: c64 repair or replace?

Postby Joseph on Mon Jul 07, 2014 10:31 pm

I've purchased some din plugs from element 14, they are good quality plugs with aluminum body and a rubber strain relief although some what more expensive than the J-car items. I tend not to use j-car unless the local store has what I need.... Most of my experience has been with audio visual equipment, this is the first time I have looked into anything involving digital circuits.... I've always stuck to analogue circuits, my most recent success is a phono pre-amp with riaa compensation so this is really a big jump in circuit complexity. I have enjoyed the challenge and am currently looking for a replacement MPU or another C64, but am not willing to purchase an untested unit.... as I believe it would be false economy. (unless the C64 is really cheap) however I have been out bid on every C64 on trade me maybe I'm too cheap. I will go ahead and find another MPU even if it don't fix the problem I will have gained some great insight into fault finding and the joys of de-soldering those chips that were never designed to be removed.... Fun times!!!!
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Re: c64 repair or replace?

Postby RonTurner on Mon Jul 07, 2014 11:07 pm

I have tended to switch brands as certain ones become popular
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Re: c64 repair or replace?

Postby Joseph on Sun Jul 13, 2014 10:29 pm

Just a quick update, after the slight mishap with my C64 mpu I decided to open and clean my 1541-II before trying it out, gave it all a good clean lubed the head runners and main bearings with sewing machine oil, using cotton buds. on reassembly hooked it up and all works just great, it seems that the old disks I have still work just fine the drive seems quieter than it has ever been.... could be poor memory and hearing loss lol.
Happy as been playing all my old favorite games but have found many games I don't remember playing..... this has brought back many happy memory's, and even driven me to try and locate some of my old gaming buddies, I think this could become a very addictive hobby, my desktop will never be the same. Also found some of my own games that I wrote in basic when I was 10, and have started to try and de-bug several I never got to work properly, I am amazed at what I accomplished during that time with little more than a C64 user guide and some photocopied reference guides... I have found it very satisfying doing some simple programing..... However due to a new job direction I will be having to do lots of study so may have to put this hobby on the back burner for a wee bit, I hope everyone who drags out their old machines (or purchasing one) gets the same joy I have experienced. Thanks to all the great advice. So now thinking about the first computers I used at school, think they were a TRS 80 followed by IBM 8088 machines.... maybe they will be next.
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Re: c64 repair or replace?

Postby Joseph on Sun Jul 20, 2014 4:02 pm

I have done further inspection and testing on my C64C and have ordered a MPU from Mutant Caterpillar Games in the UK, its cheaper than buying an untested c64 on trade me, so now will see if my diagnostics are correct, providing that the chip actually turns up, a bit nervous as I don't normally purchase items from outside of NZ. now just trying to find the correct chip socket for the MPU
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Re: c64 repair or replace?

Postby Carcenomy on Sun Jul 20, 2014 4:54 pm

D'oh, life's been in the way of being on here often these days. I have a solid half dozen spare 64 boards, could have salvaged a chip for ya. Never mind, if you get in a bind for installing the chip lemme know.
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Re: c64 repair or replace?

Postby Joseph on Sun Jul 20, 2014 10:54 pm

Oh well thats how the cookie crumbles I will certainly ask for help if I get into a bind, Thanks for the offer
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Re: c64 repair or replace? (Solved)

Postby Joseph on Tue Jul 29, 2014 8:53 pm

Thanks to all for advice, I have now replaced the MPU and everything is working, the hardest part of the repair was removing to soldered in MPU which I used a solder sucker pump to remove the bulk of the solder followed by solder wick to get the rest, it took some patience but eventually the MPU fell out of the board with no damage to chip or board, I then soldered in a socket and fitted replacement chip. I can now get multi load tape program's to run and can now return my datasette to original configuration
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Re: c64 repair or replace? (Solved)

Postby tezza on Tue Jul 29, 2014 10:30 pm

That's great. I've had to desolder that chip myself once. It's not fun!
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