An interesting way to test MOS 6522 VIA chips as found in the 1541 disk drive and Vic 20
Posted: Fri May 28, 2021 8:49 pm
Not sure if anyone has come across this before.....
Recently, I was observing the behaviour of several different MOS 6522 VIA chips in a Mitsumi style 1541 disk drive.
I had received recently 4 X cheap MOS 6522 VIA chips from an Asian supplier.
The condition of these was very interesting. They came wrapped in a thick Glad wrap (Saran wrap) like material stacked into each other. They looked clean, the legs had all been dipped in solder. One of the chip's had 3 of the legs fall off on 2 insertions into a socket. I was able to save it with some bodge wire.
They had MOS branding and all the same date code. I didn't go further with trying to see if the labels were counterfeit. I was too worried that I may further compromise the chip's pins.
I am fairly certain that these are pulls from something else.
They did look convincingly original though.
I had these bought chips plus a few that I had and knew were original and in various states of operation. Some were outright dead others would partially work, others were ok.
I had tried them in a Vic 20 in the 2 different VIA sockets the marginal ones would say have no joystick control where as in the other socket the keyboard would be fine.
Just randomly, I noticed that if one placed a 6522 VIA chip under test in socket UC2 of a 1541 disk drive mainboard and had a JiffyDOS 5.0 kernal active and a full format was initiated. A fully functional VIA chip would complete the activity.
A failed or marginal 6522 VIA chip would not complete this operation. I checked as many different configurations as I could. This was the one that seemed to give a pass no-pass case.
Using the original Commodore factory kernal will pass marginal MOS 6522 VIA chips. Be aware.
Now, I did use a X1541 cable hocked up to a PC laptop running CBM Transfer just for easy usage.
Here are the steps I used ......
I initialized the disk by powering up the drive.
Read the error channel (check the drive status button in CBM Transfer).
If it reports anything other than.... 73,jiffydos 5.0 1541,00,00
It's failed the test.
Then start a complete disk format (warning this will erase everything on the disk). It's fast.
Again read the error channel (check the drive status button in CBM Transfer).
Check to see if OK appears.
Load the disk's directory and list it.
If it comes back OK then the MOS 6522 VIA chip has successfully passed testing.
I would say without a doubt that this operation can be achieved on the real C64 breadbins and C64C hardware without any JiffyDOS running inside the C64 computers themselves. JiffyDOS needs to in the 1541 disk drive, though.
There must be some 1541 JiffyDOS 5.0 kermal routines that fully exercise the MOS 6522 when it's in socket UC2.
Maybe someone out there can confirm or deny this observation.
Recently, I was observing the behaviour of several different MOS 6522 VIA chips in a Mitsumi style 1541 disk drive.
I had received recently 4 X cheap MOS 6522 VIA chips from an Asian supplier.
The condition of these was very interesting. They came wrapped in a thick Glad wrap (Saran wrap) like material stacked into each other. They looked clean, the legs had all been dipped in solder. One of the chip's had 3 of the legs fall off on 2 insertions into a socket. I was able to save it with some bodge wire.
They had MOS branding and all the same date code. I didn't go further with trying to see if the labels were counterfeit. I was too worried that I may further compromise the chip's pins.
I am fairly certain that these are pulls from something else.
They did look convincingly original though.
I had these bought chips plus a few that I had and knew were original and in various states of operation. Some were outright dead others would partially work, others were ok.
I had tried them in a Vic 20 in the 2 different VIA sockets the marginal ones would say have no joystick control where as in the other socket the keyboard would be fine.
Just randomly, I noticed that if one placed a 6522 VIA chip under test in socket UC2 of a 1541 disk drive mainboard and had a JiffyDOS 5.0 kernal active and a full format was initiated. A fully functional VIA chip would complete the activity.
A failed or marginal 6522 VIA chip would not complete this operation. I checked as many different configurations as I could. This was the one that seemed to give a pass no-pass case.
Using the original Commodore factory kernal will pass marginal MOS 6522 VIA chips. Be aware.
Now, I did use a X1541 cable hocked up to a PC laptop running CBM Transfer just for easy usage.
Here are the steps I used ......
I initialized the disk by powering up the drive.
Read the error channel (check the drive status button in CBM Transfer).
If it reports anything other than.... 73,jiffydos 5.0 1541,00,00
It's failed the test.
Then start a complete disk format (warning this will erase everything on the disk). It's fast.
Again read the error channel (check the drive status button in CBM Transfer).
Check to see if OK appears.
Load the disk's directory and list it.
If it comes back OK then the MOS 6522 VIA chip has successfully passed testing.
I would say without a doubt that this operation can be achieved on the real C64 breadbins and C64C hardware without any JiffyDOS running inside the C64 computers themselves. JiffyDOS needs to in the 1541 disk drive, though.
There must be some 1541 JiffyDOS 5.0 kermal routines that fully exercise the MOS 6522 when it's in socket UC2.
Maybe someone out there can confirm or deny this observation.