My favorite C64 is broken, help!

[OBSysteme]

I've got a very nice Commodore 64 breadbin model in super shape... only... a few months ago, it started malfunctionning.

Only one thing is wrong with it. It can't load from the dataset anymore!

It can do all the rest perfectly from a Disk drive.

When loading a cassette.. it seem to do as if all is normal but when you then run the program nothing happens. Also on some programs he will get a load error while reading from the tape.

Thi is not fatal as I can work with it from disk, but it is truely annoying and I want to cure this.

Does anyone know what could cause this or what chip to change?

I know one specific chip is supposed to deal with loading and communicating with peripherals, but how is it that the disk drive works perfectly with it?

NOTE: the datassette itself works as I have run it with other C64's I have.

NOTE2: the problem seem to have occured on a very hot and humid day, if that helps.

any lead is appreciated.



thanks.

[saehn]

Try asking at Lemon64. There are many more C64 people over there.

[RobertBe]

When loading a cassette.. it seem to do as if all is normal but when you then run the program nothing happens. Also on some programs he will get a load error while reading from the tape.

This is not fatal as I can work with it from disk, but it is truely annoying and I want to cure this.

I would have said that it was the datasette that was malfunctioning, but you've said that it works fine with your other C64s. The only other thing I can think of is that the C64 is not providing the proper line voltage/amperage to the datasette. Can you measure the voltage/amperage at the datasette port of the C64? Are the contacts shiny, clean, and intact on the C64's datasette port?

Back in California for a few days,
Robert Bernardo
Fresno Commodore User Group
http://videocam.net.au/fcug
The Other Group of Amigoids
http://www.calweb.com/~rabel1/
Southern California Commodore & Amiga Network
http://www.sccaners.org

[OBSysteme]

Hey Robert, good leads, I'll get on it as soon as I can... it would be nice if it turned out to be as simple as that.

One thing.. I do remember that the problem came gradually... meaning that at some point I could load a simple program... but not a bigger/longer one... so it could be that the things works but fails at some point, and it got worse (Now it can load anything apparently).

so your idea of "bad voltage/contact" could explain this.

[arkanoid_376970]

@ sahen
could it be the PLA screwing up?

[e5frog]

First thing to check is that you have the right voltage from the power supply as these are known to break. Measure and check the 5V inside the C64.
The power supplies are called "black bricks" because they will silently kill your C64 when they break as the voltage on the 5V line increases and busts the sensitive chips. They have no protective circuits.


Then I would unplug and replug all chips in sockets (perhaps even a few times) as the connection between chip and socket gets worse as time goes by because of oxidation - until the resistance is too high for a proper connection. Doing this simple maneuver can solve a lot of problems (and/or prevent a lot). That goes for ALL old electronics.


Another thing that usually breaks are the electrolytic caps, it's best to swap all of them for new ones with the same value. I recently did this "re-cap" on one of my machines and most of them are the same kind. This also goes for ALL old electronics (as "young" as the Amiga 600 even)

Ray Carlsen's pages are a wealth of knowledge:
http://personalpages.tds.net/~rcarlsen/cbm/c64-ic.txt
http://personalpages.tds.net/~rcarlsen/cbm.html


If you check the schematics here you can see what components are directly attached to the cassette port:
http://www.zimmers.net/anonftp/pub/cbm/ ... uters/c64/
I don't know which revision of C64 you have but you'll find one example here:
http://www.zimmers.net/anonftp/pub/cbm/ ... 9-2of2.gif

As you can see some of the cassette signals (upper right in the picture above) end up in the 6510 (the CPU), if that's socketed some re-seating may help. One or more of the components between it and the cassette port may be broken or you may need to replace the 6510 itself.

You can also see that the cassette READ goes into the CIA 6526 at U1. The 6526 is also a part that breaks often (there are two).
You can try and swap these two and see if it starts to work again (and then replace the faulty one if it does). If it's socketed, try re-seating it first.


I'd see what Ray has to say about it first (if any).

[GreyGhost]

I don't have much knowledge with the electronic side of things, but my cassette player started acting up. But I bent little connectors inside the cassette plug down a little and it worked fine again.

[e5frog]

The connector-pins of all my datasette connectors reach all the way to the other side of the plastic - touching it. But perhaps there's a chance of improvement if you clean them and the mating surfaces on the C64 tape port.

[OBSysteme]

Thanks guys for all the feedback, I am keeping all these comments and will start checking things as soon as I get some time.

One thing... I did use it with a suspicious black brick... some time ago I only had one and seemed to work fine, but it did have a small crack and later comparing it to a second brick I got, found that it was slightly buldged.



We'll see, I hope to prevail in getting it in top shape again.

cheers !

OBS