VIC-20 Motherboard repair/questions/PAL conversion/IC population

[DistantStar001]

So I recently got this motherboard for an early (assuming due to the glass capacitors) two-prong VIC-20. I was told it works (at least it would if it were populated with all its missing IC's) with the exception of a bad power switch. I've repaired the switch (just some gummed up flux that was sticking it a bit in the off position), but there seems to be a modification on it where the fuse goes. A small red wire with what appears to be a green capacitor has been used to bridge the connection.

My questions on this are: Is this safe or should I remove it and put a fuse? If it is safe, then is it better than the fuse? And if so, would there be any serious benefit to doing a similar mod to my other VIC-20?

As for the missing IC's, I've managed to source just about all of them (VIA's, CPU, and even an NTSC VIC), but what I haven't found are the ROMs.

What I'd really like to do is turn this into a PAL machine. However, from what I've been told I will need a PAL Kernel ROM and a 6561 VIC. I have no idea where to find these. For that matter, I'm not sure where to get any of the ROMs (Kernal, BASIC, or Character), PAL, NTSC or otherwise. Also, is this all I need to do, or is there more to a PAL conversion on this board?

I've found a few VICs (some of which are even reasonably priced below what I paid for a full VIC-20). But those are 6560's. So not quite what I'm looking for.

As such, I'm putting it out there. Does anyone know a good source to find these chips at a reasonable price (preferably less than $40 collectively)? Or am I out of touch with the current market? It's Just, aside from the VIA's and 6502, I will also need to get a case (just the bottom half, as I have a top) and find the missing keys to my spare keyboard (found most, but the 'INST/DEL' key is nearly impossible to find), and I'm trying to keep this project within my budget (i.e less than what it would cost to import a full PAL VIC-20).

As always any suggestions or advice is appreciated.

Oh! And here's a picture of the not quite complete motherboard:

Screen Shot 2020-12-21 at 10.10.32 PM.png[/attachment]

[srowe]

My questions on this are: Is this safe or should I remove it and put a fuse? If it is safe, then is it better than the fuse? And if so, would there be any serious benefit to doing a similar mod to my other VIC-20?

It might be some form of thermal fuse, for safety I would replace it with the correctly rated fuse.

As for the missing IC's, I've managed to source just about all of them (VIA's, CPU, and even an NTSC VIC), but what I haven't found are the ROMs.

What I'd really like to do is turn this into a PAL machine. However, from what I've been told I will need a PAL Kernel ROM and a 6561 VIC. I have no idea where to find these. For that matter, I'm not sure where to get any of the ROMs (Kernal, BASIC, or Character), PAL, NTSC or otherwise. Also, is this all I need to do, or is there more to a PAL conversion on this board?

Do you want to use original ROMs or would you settle for an EPROM in an adapter? The latter is an easy and cheap option. Otherwise there was a UK seller on eBay recently that had a batch of NOS ROMs. To convert between NTSC and PAL will require other changes, the oscillator is a different frequency and there are a few other components to change.

[DistantStar001]

It might be some form of thermal fuse, for safety I would replace it with the correctly rated fuse.

Not a problem. Also, I'm guessing that I should leave my other VIC the way it is.

Do you want to use original ROMs or would you settle for an EPROM in an adapter? The latter is an easy and cheap option.

I'd prefer originals, but if the latter is cheaper, I'll go with it. Where do I get them?

To convert between NTSC and PAL will require other changes, the oscillator is a different frequency and there are a few other components to change.

Can I assume that the oscillator is the same as the C64? And what other components do I need? Is there a guide or instructional video?

[srowe]

I'd prefer originals, but if the latter is cheaper, I'll go with it. Where do I get them?

You don't say where you're located, Jim Brain sells these

http://store.go4retro.com/2364-adapter/

which can be used for the KERNAL and BASIC ROMs. I don't think they work for the character ROM.

Can I assume that the oscillator is the same as the C64? And what other components do I need? Is there a guide or instructional video?

No, the PAL C64 clock is 0.985 MHz, the VIC 20 is 1.108 MHz.

I've only seen a guide going in the other direction

http://webcache.googleusercontent.com/s ... irefox-b-e

[DistantStar001]

You don't say where you're located

That would be helpful. I'm in the bay area, California, USA.

Jim Brain sells these

http://store.go4retro.com/2364-adapter/

The problem here is that I don't have the ability to program the EPROM, so I guess that puts me back at the original ROMs. Unless someone has them pre-programmed.

I've only seen a guide going in the other direction

http://webcache.googleusercontent.com/s ... irefox-b-e

OK. So according to this, the board I have probably can't be converted. The PAL board has an IC at UB 10, which doesn't exist on the NTSC board. So this will stay an NTSC VIC. Cool! I can always use a backup. Just transplanted a 6502 (not 65c02) from an unenhanced //e, and can get the VIA and VIC sometime this week (and a new fuse). Now all I need to find are the ROMs. Progress!!!

[DistantStar001]

So I've run into an interesting... not quite problem... More like a difference, and I'm not quite sure which is correct.

I got a new (old stock) VIC chip and installed it, and yesterday I stopped by my local electronic recycler where they happened to have a VIC-20 for sale. I bought it figuring that I could use it to swap chips without risking damage to my PET-style (really love that thing). I hooked it up, and it works perfectly. Then I temporarily transplanted the ROMs to test to see if my motherboard really was fully functional. The good news is that it works. However, the border color is different than my other two VIC's. More greenish, where the other two are very blue. The thing is that the color seems closer to what I see in YouTube videos of other VIC-20's and on VICE. On the other hand, the two VIC's that I have both display the blue border.

Pictures are below. Maybe someone can clue me in as to which is correct, and how to adjust it?

By the way. The lack of a cursor on the third screen is related to the current lack of VIA chips. I'll be getting them soon.

[srowe]

Pictures are below. Maybe someone can clue me in as to which is correct, and how to adjust it?

The bottom picture looks more normal. There's a trimmer in the video circuit that can be adjusted.

[DistantStar001]

Pictures are below. Maybe someone can clue me in as to which is correct, and how to adjust it?

The bottom picture looks more normal. There's a trimmer in the video circuit that can be adjusted.

OK! So an interesting discovery! Looking inside the video box, I found three trimming pots. Two plastic ones were housed with the VIC chip and one metal in the smaller compartment. Working from left to right, I tried adjusting each. The first seemed to affect the brightness of the picture, the second did nothing at all, and the metal one was sealed with wax. I broke the seal (can always reseal later) and got either color, monochrome or black screen depending on which way I turned it. However, there was no effect on the background color from any of the pots. So then I opened up my PET -style and started comparing date codes. Not surprising, the PET-style was from 1981, my other two are dated 1982. But the other computer has a VIC manufactured in the 32nd week of 82, where the VIC I got for the motherboard is from the 50th week. This made me think, maybe later VIC chips produce different colors? So I swapped them. Low and behold the green-teal screen followed the newer VIC!

So I'm guessing that there must have been a change in the manufacturing of VIC chips that occurred at some point before the 50th week of 1982.