A Tale Of Two C-64's

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A Tale Of Two C-64's

Postby zzap64 on Wed Feb 04, 2015 8:24 am

Hi guys, first time caller here. I recently brought two immaculate C-64's but unfortunately for me, neither of them work. One refuses to power up, the other powers up but comes up with a" ?OUT OF MEMORY ERROR IN O" message. Now I know the obvious thing to do would be to take both of them apart and swap the good with the bad but alas I lack the skills to do so and was wondering if there's anyone on here or out there who still repairs C-64's?

Regards, Jason
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Re: A Tale Of Two C-64's

Postby RonTurner on Wed Feb 04, 2015 8:29 am

Could be a bad 4164 , what part of the country are you located, maybe there is a local C64 collector who can help.
Last edited by RonTurner on Wed Feb 04, 2015 8:32 am, edited 2 times in total.
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Re: A Tale Of Two C-64's

Postby zzap64 on Wed Feb 04, 2015 8:30 am

Hi Ron I'm in Wellington, Porirua to be exact :D
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Re: A Tale Of Two C-64's

Postby RonTurner on Wed Feb 04, 2015 8:32 am

How much RAM does it say it has on the top of the screen when you boot it ?
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Re: A Tale Of Two C-64's

Postby zzap64 on Wed Feb 04, 2015 8:36 am

I can't remember what the bytes free on to of the screen said but all I can say is it came up with a big fat zero :lol: Now I know it's more than likely bad ram so I could just replace the bad power unit with the good one and vice versa with the board but I wouldn't even begin to know where to start?
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Re: A Tale Of Two C-64's

Postby SpidersWeb on Wed Feb 04, 2015 8:48 am

C64's aren't my specialty (but I've worked on them before and have 3 running units myself - plus 4164 and 41464 ICs on hand (depending on which type of 64 it is) and desoldering pump / solder station, tested supplies and monitors and cables and way too many joysticks. Actually have a Commodore 1802 on my dining room table at the moment.

Long story short - I live in Porirua and in conjunction with advice from these guys I'd be happy to help out if needed - I'd be around home Fri/Sat/Sun, wife is away at a wedding so I'll be making a mess anyway.
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Re: A Tale Of Two C-64's

Postby Clym5 on Wed Feb 04, 2015 8:52 am

If it is RAM, you can usually tell what chip it is by feeling the tops of them. If one or more are hotter than the others, that would be the bad chip. That tip sure helped me quite a few times.
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Re: A Tale Of Two C-64's

Postby zzap64 on Wed Feb 04, 2015 8:55 am

I have two bread box models, in near perfect condition, real shame the buggers don't go. But I'm sure between the two of them, a live one can be born :D I'm thinking replace the power unit in the first one to see if all it was in that one was a faulty power unit?

In any case I'm in Aparangi Cresent
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Re: A Tale Of Two C-64's

Postby RonTurner on Wed Feb 04, 2015 10:25 am

You should also test your 30 year old PSU , that could have fried your RAM.
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Re: A Tale Of Two C-64's

Postby zzap64 on Wed Feb 04, 2015 12:09 pm

I have a mate who's an electrician so at the very least he'll be able to test the PSU with a voltage meter to see if anything's amiss there
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Re: A Tale Of Two C-64's

Postby mrad01 on Wed Feb 04, 2015 8:09 pm

zzap64 wrote:I have a mate who's an electrician so at the very least he'll be able to test the PSU with a voltage meter to see if anything's amiss there


You need to do more than that. They can be fine for a while, then suddenly go wildly up and down. I have a plug with a 12v DC bulb on it which I connect to the DC side of the PSU and watch it for 20 mins. If the bulb goes bright/dim/bright at any time - bin the PSU.
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Re: A Tale Of Two C-64's

Postby zzap64 on Wed Feb 04, 2015 8:58 pm

Good point, will do. And thanks heaps for the heads up
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Re: A Tale Of Two C-64's

Postby Gibsaw on Thu Feb 05, 2015 11:36 am

mrad01 wrote:
zzap64 wrote:I have a mate who's an electrician so at the very least he'll be able to test the PSU with a voltage meter to see if anything's amiss there


You need to do more than that. They can be fine for a while, then suddenly go wildly up and down. I have a plug with a 12v DC bulb on it which I connect to the DC side of the PSU and watch it for 20 mins. If the bulb goes bright/dim/bright at any time - bin the PSU.


And by "bin the PSU", he means pull out it's innards and replace it with the innards from two (5V DC and 9V AC) appropriate quality modern wall warts. :)
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Re: A Tale Of Two C-64's

Postby zzap64 on Fri Feb 06, 2015 12:24 pm

Would there be anyone who could test and gut one for me if need be?
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Re: A Tale Of Two C-64's

Postby SpidersWeb on Fri Feb 06, 2015 6:45 pm

Now that they're visiting my place at the moment, I've been messing around with them.
I haven't tested the power supplies yet, just using my own which I tested on one of my units this morning for a few hours.

The black screen C64 I'm pretty confident has something funky going on in the power-side of the PCB.

The "NO MEMORY AT 0" machine was fine in this respect, displayed the message and dropped me at a READY prompt.

First I checked for a hot DRAM chip, or one that was slightly discouloured, but no physical signs. Since I had the ready prompt, I figured I'd try a mini RAM test program squished in to one line:

FOR I=2060 TO 40000: POKE(I,255): <verison of code to check RAM contents> NEXT

However this really didn't have the predictable results I'd hoped for that could point to a specific chip. I was hoping to see a specific bit being stuck on, but it appeared almost random. As a last resort, I pulled a random 4164 chip out of a dead 8088 motherboard, and started piggybacking.

Image

On the first try :shock:
Still needs testing and the chip properly soldered in, but pretty happy to see it start up.
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