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CBM PET 8296-D KEYBOARD PROBLEMS
- Thread starter Desperado
- Start date
daver2
10k Member
>>> You say to change the capacitors?
No, I didn't say that...
You have two (2) disk drives, do both of them do the same thing?
I would try some different media first. See if you can find some?
Interesting read at: https://forum.vcfed.org/index.php?threads/commodore-pet-acquisitions.12310/. I knew VCFED was a good site
!
You may find that your DS/DD disks will work - but they also may not. The 100 tpi disk drives 'half step' so QD disks are certified for use, whereas DD ones may not be. They may still work, but may also be unreliable. There seems to be a whole lot of confusion around this. I definitely remember using DS/QD disks at one time or another.
Ah-ha. I have found a photograph of a pack of DS/QD disks (96tpi): https://www.worthpoint.com/worthopedia/datalife-verbatim-ds-qd-25-inch-276440143. They do exist after all!
There is a very good write-up here also: https://www.retrotechnology.com/herbs_stuff/drive.html.
Older DS/DD disks may not be the same as more modern DS/DD disks. It depends upon whether they were designed for 40 or 80 track use. Some manufacturers identified DS/DD 80 track disks as QD. Others didn't. It is possible that some disks identified as DS/DD may be suitable, but older disks may not be... Why can't anything be simple.
What I do know is not to use HD (High Density) disks designed for an IBM-PC (or clones). These use magnetic material that is definitely incompatible with the type of disk drives you have.
Dave
No, I didn't say that...
You have two (2) disk drives, do both of them do the same thing?
I would try some different media first. See if you can find some?
Interesting read at: https://forum.vcfed.org/index.php?threads/commodore-pet-acquisitions.12310/. I knew VCFED was a good site
!You may find that your DS/DD disks will work - but they also may not. The 100 tpi disk drives 'half step' so QD disks are certified for use, whereas DD ones may not be. They may still work, but may also be unreliable. There seems to be a whole lot of confusion around this. I definitely remember using DS/QD disks at one time or another.
Ah-ha. I have found a photograph of a pack of DS/QD disks (96tpi): https://www.worthpoint.com/worthopedia/datalife-verbatim-ds-qd-25-inch-276440143. They do exist after all!
There is a very good write-up here also: https://www.retrotechnology.com/herbs_stuff/drive.html.
Older DS/DD disks may not be the same as more modern DS/DD disks. It depends upon whether they were designed for 40 or 80 track use. Some manufacturers identified DS/DD 80 track disks as QD. Others didn't. It is possible that some disks identified as DS/DD may be suitable, but older disks may not be... Why can't anything be simple.
What I do know is not to use HD (High Density) disks designed for an IBM-PC (or clones). These use magnetic material that is definitely incompatible with the type of disk drives you have.
Dave
Last edited:
daver2
10k Member
>>> Maybe i need new discs and the right format.
I think so.
Dave
I think so.
Dave
daver2
10k Member
The only place I would think of would be thingiverse.
If memory serves me correctly, these are screw on aren’t they (with a single screw from the front).
I am sure you should be able to find a similar ‘donor’ floppy drive on eBay?
Dave
If memory serves me correctly, these are screw on aren’t they (with a single screw from the front).
I am sure you should be able to find a similar ‘donor’ floppy drive on eBay?
Dave
Desperado
Veteran Member
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Desperado
Veteran Member
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Unfortunately i can't find any this spare on ebay
I am desperate!!
daver2
10k Member
It doesn’t have to be specifically this disk drive.
See what you can find that is similar and lookup the specification for that drive online and see how the handle attaches.
If it is the same (or similar) and the drive is cheap, then it may be worth a try. You may have to make some minor modifications.
Dave
See what you can find that is similar and lookup the specification for that drive online and see how the handle attaches.
If it is the same (or similar) and the drive is cheap, then it may be worth a try. You may have to make some minor modifications.
Dave
dave_m
Veteran Member
The floppy spec for the 8250 says 100 tracks per inch (TPI) double-sided with capacity for 1,066,496 bytes. 154 tracks, 77 on each side. Manual said it uses a Micropolis Tandon drive. I would use this type of diskette unless you are looking for problems and willing to try a lot of DSDD ones until you get one to work. This drive will be much more picky than a 8050 drive.
dave_m
Veteran Member
We need some Commodore 8250 drive users to chime in on this issue.
Here is what I found on the internet which is not too helpful:
Quad density (QD or 4D) doubles capacity over DD by narrowing the width of tracks to 0.160 mm (0.0063 in) for a density of 96 tpi. Some manufacturers (Micropolis, Tandon, Micro Peripherals (MPI), Teac) used a track density of 100 tpi for quad-density drives, which were incompatible with 96 tpi models.
High density (HD) improves capacity by utilizing a 96 tpi track density in conjunction with improved cobalt disk coating and stronger 600-oersted write heads, allowing 9646 bpi to be written.
en.wikipedia.org
==================================================================
So daver2 is right that HD floppies will probably not work. And while 100 TPI drives will not read 96 TPI formatted floppies, that does not mean that 96 TPI rated floppies will work not in a 100 TPI drive. It is just not guaranteed. You may want to try the highest quality brands of DSDD 96 TPI floppies to have the best chance of them working with your 8250. As the chances of finding quad density 5 1/4 floppies rated at 100 TPI are not good.
Here is what I found on the internet which is not too helpful:
Quad density (QD or 4D) doubles capacity over DD by narrowing the width of tracks to 0.160 mm (0.0063 in) for a density of 96 tpi. Some manufacturers (Micropolis, Tandon, Micro Peripherals (MPI), Teac) used a track density of 100 tpi for quad-density drives, which were incompatible with 96 tpi models.
High density (HD) improves capacity by utilizing a 96 tpi track density in conjunction with improved cobalt disk coating and stronger 600-oersted write heads, allowing 9646 bpi to be written.
Disk density - Wikipedia
So daver2 is right that HD floppies will probably not work. And while 100 TPI drives will not read 96 TPI formatted floppies, that does not mean that 96 TPI rated floppies will work not in a 100 TPI drive. It is just not guaranteed. You may want to try the highest quality brands of DSDD 96 TPI floppies to have the best chance of them working with your 8250. As the chances of finding quad density 5 1/4 floppies rated at 100 TPI are not good.
daver2
10k Member
Job’s a good ‘un!
Not all floppy disks are created equal...
Dave
Not all floppy disks are created equal...
Dave
daver2
10k Member
My gut feeling would be the character generator or the socket for the character generator.
However, there appears to be other lower case letter o’s on the screen that don’t appear to exhibit the problem.
I would need more information about which characters in which locations on the screen are ‘twinkling’.
Dave
However, there appears to be other lower case letter o’s on the screen that don’t appear to exhibit the problem.
I would need more information about which characters in which locations on the screen are ‘twinkling’.
Dave
daver2
10k Member
Since you have BASIC available, write a little BASIC program to POKE known characters into the screen, PEEK the values back and compare the value read with what should be there. Put it in a loop and see if it detects any anomalies. If no anomaly’s are detected, it is not the video RAM or buffers, so must be within the later logic generating the video stream.
Dave
Dave