Resurrecting an old VIC.

[Witzo]

Thanks to Lee's PC power supply-to-VIC instructions, since yesterday I am the proud owner of a running VIC20:



My big TV works well with it.
I'm really pleased to see a live VIC20 again after 25 years!

Was quite a tense moment yesterday when I finally had all the parts soldered together: I don't know the history of this machine so couldn't even be sure it worked. But it does!

I only have two problems that maybe you guys can give some advice on:
- The restore key doesn't work when I want to interrupt something with run/stop-restore. I'm not sure if it's totally broken or just doesn't work in combination with run/stop. What's the scan code for Restore?

- I connected a 1571 disk drive which works (I use it with my C128), but the VIC doesn't seem to talk much to it: upon LOAD"$",8, it stays stuck in SEARCHING. Which I can't interrupt with run/stop-restore, haha.
It does give a 'device not present' when I disconnect the drive, so apparently it sees the drive but does nothing more.

Does the MegaCart have an SD card slot? If I can move programs from my mac to the vic that way, I'm definitely in the market for one.

[16KVIC20]

Hi, no the Mega Crat does not have a slot for a card. Somebody was trying to make a Mega Cart and Final Expansion in one cartridge, I don't know if it was ever completed though.

[Jeff-20]

I only have two problems that maybe you guys can give some advice on:
- The restore key doesn't work when I want to interrupt something with run/stop-restore. I'm not sure if it's totally broken or just doesn't work in combination with run/stop. What's the scan code for Restore?

Off the top of my head, i think it's bit 3 of location 657. So, you should get a 4 (or higher) when pressing it. I'll double check that, and someone can correct me if I'm not recalling that correctly.

[Mike]

What's the scan code for Restore?

The Restore key has no scan code. It is directly connected to pin 40 (CA1) of VIA #1 which in turn issues an NMI.

I connected a 1571 disk drive which works (I use it with my C128), but the VIC doesn't seem to talk much to it:

The signal line inputs of the serial port are also connected to VIA #1. That could indicate, that this chip may have some issues.

[Witzo]

Again you amaze me with squeezing more information out of superficial symptoms than I thought possible.

I'll open up this VIC someday, there is actually something loose in there that I hear rolling around when I pick it up.

Can you point me to a link of a picture of the VIC's motherboard with an indication where that VIA #1 lives?
The best thing I can do is check soldering points for cracks and fix those, I'm hoping maybe it's just that a few of those chip's legs have come loose.

[Mike]

See this pic. Pin 40 is located at the top-right corner of the chip:

I'll open up this VIC someday, there is actually something loose in there that I hear rolling around when I pick it up.

I'd check immediately, loose metallic parts inside can easily short out things!

[nbla000]

Does the MegaCart have an SD card slot?

Hi, no the Mega Crat does not have a slot for a card.

Yes, this is true but you may use the Mega-Cart with uIEC, SD2IEC or C64SD. All of them are full supported (fast LOAD/SAVE too) with the integrated CBM-FileBrowser.
And don't forget that you may use these SD-Drives with all other commodore machines too (C64/C16/C128 etc)

Somebody was trying to make a Mega Cart and Final Expansion in one cartridge, I don't know if it was ever completed though.

did I miss something ?

Btw the Mega-Cart + SD-Drive seems a good solution to me, if you use the C64-SD you don'd need any power supply and now you may use the External Boot feature to use the Mega-Cart as you want.

- I connected a 1571 disk drive which works (I use it with my C128), but the VIC doesn't seem to talk much to it

You need to switch the 1571 in double side mode by sending a special command to the drive before to use it on a Vic-20.

Example for drive 8

Code: Select all

OPEN 15,8,15,"U0>M1":CLOSE15

[tokra]

You need to switch the 1571 in double side mode by sending a special command to the drive before to use it on a Vic-20.

Example for drive 8

Code: Select all

OPEN 15,8,15,"U0>M1":CLOSE15

Only if you really want to use a double-sided disk. Normally you would not need to send any command if you use single-sided disks or just flip them over.

Regarding SD-drives. On the Revision party I spoke to someone who realized a "Power over Serial"-drive, so you would not need an extra tape-port adapter. This uses the reset-line for power. There were some small drawbacks I don't remember too detailed - but I thought the idea was really nice - if you're interested (and know german) see here:

http://www.dienstagstreff.de/projekte/e ... /index.php

[nbla000]

Regarding SD-drives. On the Revision party I spoke to someone who realized a "Power over Serial"-drive, so you would not need an extra tape-port adapter. This uses the reset-line for power.

This is a good idea btw the C64-SD does not require nothing, just plugs it on your C64 or Vic-20 and play, you need a serial cable and external power just for all other Commodore machines, C16, C128 etc etc. but not for C64 and Vic-20.

My typical Vic setup is Vic-20+C64-SD+Mega-Cart, I need only the video cable and the Vic-20 power supply of course.

[Witzo]

Thanks for all the tips!
I think I'll get one of those Manosoft C64SD cards, since the Final Expansion seems out of stock.

AFAIK the 1571 starts up as a 1541, or at least single sided, when connected to a C64. I expected the same for the VIC. I had a single sided floppy inserted when I tested it yesterday.

I opened up the Vic, found one of the six motherboard screws loose (put it back where it belongs), cleaned some dust out, and inspected the solderings. Didn't find anyhting bad. The VIA #1 was in a holder, different from the one left of it, and different from Mike's example.


big: http://i.imgur.com/OFc0C.jpg


On the bottom was a blue wire from one point of the cartridge port to somewhere in the VIC I's area. Is that supposed to be there?


big: http://i.imgur.com/ehpBH.jpg

[Mike]

On the bottom was a blue wire from one point of the cartridge port to somewhere in the VIC I's area. Is that supposed to be there?

In early versions of the CR mainboard, this wire connects pin Y of the expansion port to the audio amplifier circuitry, for AUDIO IN. This wire and the included shrinked 1 kOhm resistor were later incorporated into the PCB layout.

You could test for continuity between Pin 40 of VIA #1 and the corresponding Pin of the keyboard connector (there are two pins separated by a wider gap, it's the one nearer to the user port). The Restore key connects that Pin of the keyboard connector to ground, you should see continuity between the two pins separated by the gap on the keyboard socket (that one connected with lots of wires to the keyboard itself) when the Restore key is pressed down.

P.S.: these images are very wide, and make this thread hard to read. Could you replace them with thumbnailed versions + links to the originals?

[Witzo]

In early versions of the CR mainboard, this wire connects pin Y of the expansion port to the audio amplifier circuitry, for AUDIO IN. This wire and the included shrinked 1 kOhm resistor were later incorporated into the PCB layout.

You could test for continuity between Pin 40 of VIA #1 and the corresponding Pin of the keyboard connector (there are two pins separated by a wider gap, it's the one nearer to the user port). The Restore key connects that Pin of the keyboard connector to ground, you should see continuity between the two pins separated by the gap on the keyboard socket (that one connected with lots of wires to the keyboard itself) when the Restore key is pressed down.

Aha, never knew the VIC actually had an analog audio IN. I'll ask about its use some other time

I know little about electronics. How do you test for continuity? Open it up and while the Vic is running, put the two ends of my voltmeter on those two places? I worry I might short circuit something.

Are VIA chips still available? This one is easy to replace because of the socket.

Code: Select all

OPEN 15,8,15,"U0>M1":CLOSE15 

is accepted without locking up the Vic, but a subsequent LOAD"$",8 still puts it in an endless uninterruptable SEARCHING.
I searched a 1571 manual but couldn't find the command to put it explicitly in single-side mode. Nbla00, do you know it? U0>M0 maybe?

Edit: found it, indeed U0>M0 for 1541 mode.

[Mike]

I know little about electronics. How do you test for continuity?

You do these tests without the VIC-20 being powered on, with your voltmeter being set to resistance measurement. The result should be very small, in the order of 0.4 ... 1.0 Ohms.

Are VIA chips still available?

In principle, yes. For the NMOS originals, eBay's probably your best friend. They had also been used in the 1541 disk drive, so could be scavenged from defective units. There's also a CMOS version of the 6522 available from WDC, but from what I've read on forum.6502.org, it is not 100% hardware compatible to the NMOS version.

Aha, never knew the VIC actually had an analog audio IN.

Only the CR models do have that feature built-in (even though it can easily be retrofitted to the older 2-prong models).

[Witzo]

There is one other thing that at first I thought was a fluke of my TV or the ever sensitive RF modulator: often, the screen is at the bottom of the TV screen. The lowest character line then disappears below the edge of my TV.
Does this point to the VIC I register for Y-position having a weird value on start up?
Sometimes the screen is on the right spot, sometimes it's moved down.

Edit: I touched the screws inside the RF modulator and the screen jumped up , or down, or freaked out. So it was the RF, not the Vic.

[Witzo]

I know little about electronics. How do you test for continuity?

You do these tests without the VIC-20 being powered on, with your voltmeter being set to resistance measurement. The result should be very small, in the order of 0.4 ... 1.0 Ohms.

Thanks, I can try that tomorrow.
Edit: to awake to go to bed yet
So I tried it, resistance went to 0. So I understand it's working.
(Tried between that user port-nearest keyboard pin at the gap and the VIA pin in your picture:0 Between the same keyboard pin and some other VIA pins: lots of resistance.)

Does this mean replacing the VIA#1?