Datasette not loading properly.

[Jumpman1981]

Hey all.

 

A while ago, I posted about a box of Commodore parts that I was randomly given. Most of it is scraps that I'll probably sell off, but one of the things I decided to hold onto is a Datasette. 

The thing is, it's having issues loading the tape. I've managed to figure out that it's a mechanical issue, as it loads perfectly fine through one of those aux-to-cassette adapters. 

 

Basically, whenever I go to load a program, I'll start the tape and the Commodore just won't find anything, or it will start loading properly, only for the Commodore to report that it's

found a string of garbage and/or give an Out Of Memory error. I know it's not the Commodore or the Datasette's electronics, because, as mentioned above, using a cassette adaptor loads things perfectly. 

 

I've done some repairs on cassette decks before, so I've already checked belts, head alignment, etc, but no luck. I have a feeling that it may have something to do with the speed, but I can't think of anything that could affect it outside of the motor. I will note that one of the Commodores in the same box was PAL, so could it be that the mechanism's been set up for 50hz?

 

Any ideas?

Edited September 23, 2021 by Jumpman1981

[carlsson]

The head alignment you did, was that regarding the azimuth angle of the head towards the tape? What happens if you take a blank tape, record a short program and load it back? The tape recorder is powered by 6V DC IIRC so doubtfully there is a speed issue. However data recorded on the tape depends on the host computer, so if you're loading a NTSC tape on a PAL machine, it might be too fast and you're getting gibberish even if the head is correctly aligned. Vice versa I think works better since a PAL C64 runs at roughly 0.98 MHz while NTSC is 1.01 MHz.

[Jumpman1981]

I did adjust the head azimuth, but I don't have any blanks to hand so I can't do the save-and-load test.

 

I didn't know that the data speed depended on the computer, I thought it was like normal tape decks where the tapes themselves are universal and the mechanisms have slight differences in them to run at the same speed on both frequencies. 

 

Edit: here's a pic of the insides for reference:

 

 

Edited September 23, 2021 by Jumpman1981

[carlsson]

The tape moves at the same speed for all systems, but the data rate of D/A converted signals depends on the system clock.

[Jumpman1981]

Ah right... I thought it was the other way around. I still don't get how it's able to load fine if I use an adaptor and play the tapes through my Walkman.

[carlsson]

Is that a real belt, or a rubber band?

[Jumpman1981]

It's a band, but it's only a placeholder. When I initially started working on it, the original belt had stretched and was beginning to perish, so I found a band that was roughly the same diameter to see if the original being loose was the problem. I only left it in as a reference for how the real thing goes through the mechanism.

[carlsson]

I'm no mechanic but I wonder if the tape will move smooth enough with that in place or if it is too elastic, causing an uneven movement and thus load errors?

[Jumpman1981]

I imagine if it's loose enough, it might do to indicate if the belt's a problem. Not something you'd fit permanently, but enough to see if there's any other potential issues. 

Edited September 23, 2021 by Jumpman1981

[Mr SQL]

On 9/23/2021 at 2:01 PM, Jumpman1981 said:

I did adjust the head azimuth, but I don't have any blanks to hand so I can't do the save-and-load test.

 

I didn't know that the data speed depended on the computer, I thought it was like normal tape decks where the tapes themselves are universal and the mechanisms have slight differences in them to run at the same speed on both frequencies. 

 

Edit: here's a pic of the insides for reference:

 

 

You may have a different playback speed from changing the belt. Your walkman is calibrated since it's loading so you could measure 15 seconds on a cassette using a magic marker to mark the spot and turn the adjustor screw on the Commodore if it doesn't match.