Vic20 repair after disk drive power up bad sequence

[rgrocha]

Hi,

Tonight I had an accident testing one disk drive with my VIC (CR).

I connected them but forgot to power up the disk drive before the VIC. After that the screen got some garbage and after reboot without the drive just a blank screen.

I followed Carlsen guide and checked mayor chips and those marked as black or blank screen culprits without any luck. UB4/7406 was bad and I replaced it. No luck, still blank screen. Then I checked VIC, CPU, VIAs, memory and some other logic ones and all of them were ok, including Kernal and Character ROMs . They were all already socketed so it was an easy task.

Any clue what could have happened and what should I test now?

Thank you

[ral-clan]

Can this REALLY break a VIC-20? I've heard it mentioned to power up the peripherals before power up the VIC, but what harm can it do? I say this because as a kid with the VIC-20 and C64 we powered up the drive after the computer lots of times without a problem.

Obviously something happened with the original poster's VIC-20...but I just wonder if powering up the drive after the computer was actually the cause.

[R'zo]

Did you check the UAB3? The VIA chip there is the interface controller for the drives. Seems rational to me that it might be the first thing effected by a surge creared by drive power up. Blank screen or no screen is a symptom for this chip being bad as well.

[R'zo]

Nevermind, i just reread your post and saw you checked your vias.

[gsoravil]

Can this REALLY break a VIC-20?

Not that I've ever seen and I don't believe that it makes sense that it could. The IEC serial bus is a peer-to-peer bus with lines pulled high via resistors and pulled low by devices. If current was such that any device could be damaged then the peripherals would almost certainly damage each other if not powered on all at the exact same time. This is reinforced by the fact that two 1541s can talk to each other without a host computer connected at all. If interested, see ftp://ftp.zimmers.net/pub/cbm/programmi ... al-bus.pdf

More than likely, the drive is defective and spiked power into the VIC and/or the VIC was about to fail anyway.

Greg

[gsoravil]

This is reinforced by the fact that two 1541s can talk to each other without a host computer connected at all.

My point with this statement is that all IEC devices (computer, drives, printers) are designed to put power on the lines themselves and are all able to communicate once powered on. Since a 1541 works the same as the computer does then it doesn't make sense that the computer would be power-on-order failure prone and no other IEC devices are.

Cool proof of this is the C64 program Fast Hack 'Em by Basement Boys' Software. With two 1541s, you can load a disk copier into 1541 RAM, start a copy, and unplug (!) the C64's IEC/serial cable. The drives will continue to copy the disk and when done you can insert a new source and destination disk set into the drives and they will start a new copy process without the C64 connected. I've tried it and it works. Very cool.

Greg