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DistantStar001

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

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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?

 

 

 

950819426_ScreenShot2020-12-21at10_10_32PM.thumb.png.f4be13e290b61f31d9f4b704acd7c35a.png

 

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:

 

81814743_ScreenShot2020-12-21at10_11_18PM.thumb.png.76a732a14f5f22a2b358bc32aca53a45.png

Edited by DistantStar001

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That looks like one of those little "greenie" fuses that were used in keyboard circuits.  They were sometimes soldered to the F1 position on 486 and Pentium era PC motherboards.  Someone may have had one of those on hand and chose to use it instead of a glass fuse.   Nice that they left the fuse holder clips in place, so installing a replacement would still be easy.  :)

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9 minutes ago, RodLightning said:

That looks like one of those little "greenie" fuses that were used in keyboard circuits.  They were sometimes soldered to the F1 position on 486 and Pentium era PC motherboards.  Someone may have had one of those on hand and chose to use it instead of a glass fuse.   Nice that they left the fuse holder clips in place, so installing a replacement would still be easy.  :)

OK.  So I'm removing it.  A glass replacement is easy to find, and easier to replace.  Also it's more authentic for the board.

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Hm. I've got a PAL CR motherboard that is 95% working, i.e. everything but the floppy drive. The VIA chips seem OK, I believe it is a 740X chip that needs replacing. Bottom half but no keyboard. Shoot me a PM if you want to discuss it further.

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19 hours ago, carlsson said:

Hm. I've got a PAL CR motherboard that is 95% working, i.e. everything but the floppy drive. The VIA chips seem OK, I believe it is a 740X chip that needs replacing. Bottom half but no keyboard. Shoot me a PM if you want to discuss it further.

PM sent.  Sorry it took me so long.

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So update for those interested.  I was directed to this website by a nice person on the Denial forum:  http://webcache.googleusercontent.com/s ... irefox-b-e 

From what I can tell, unfortunately, this board can't be converted to PAL, since the NTSC boards lack a spot for the IC at UB 10 on the PAL boards.  Kind of a bummer as I really want a PAL VIC, but I'm still going to get this one going because its fun, and I love VIC-20's.  

 

To that end, I got my VIC chip a couple of days ago and a temporary ROM transplant.  The board works!!!  The only thing odd was that the background color was different from my first VIC-20.  It's a kinda greenish teal that is similar to what I get on VICE but a bit greener.  My first VIC, on the other hand, is a light but very blue color.  Yesterday, I stopped by my local electronics recycler, and as luck would have it they had a VIC-20 to sell me.  I took it home, plugged it in, and like my first VIC, I got a same blue color...  So now I'm wondering which color is right and how to adjust the then to the correct color?  By the way, the missing cursor on the third screen is because I haven't gotten the VIA's yet (and now I need the NTSC ROMs).  

729195763_VIC1.thumb.png.6dcfa141136ad6f598fc91d4c4b7f437.png1472415926_VIC2.thumb.png.7640611eab4f0cf6629bcb7a7ade7683.png600918250_VIC3.thumb.png.148be03ec494fd0f5cb3ca9194b06433.png

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Nobody seems to mention the border color. Thanks for chiming in on that!

 

My first Vic was definitely the cyan color border as in the third picture. I think it was a CR board as my parents purchased it for me a year or two after the release...round DIN power connector.

 

But, I have found in recent years that all of the earlier Vic-20 models I have acquired with the original two prong power connector (including a very old one with a 11,000 some odd serial number and a PET style keyboard) that those models have the dark blue border akin to your first two pictures.

 

And the adjustable pots do not change this. I am chalking it up that it is normal and that earlier Vic boards have the blue border as opposed to the cyan.

Edited by eightbit

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In practice you should be able to PRINT PEEK(36879) to tell what it is set to. If it tells you 27, that is cyan except that your TV is tuned to overcompensate colours, making it look blue. If it tells you 30, you really have a blue border, which I strongly doubt is the case.

 

It can be compared with the rare P500 which supposedly should have a cyan border and white background, but on some TV sets and perhaps in combination to how the pots on the motherboard are set, will make it look bright green. Many people have assumed it is green because if it looks like a pig and squeaks like a pig, it must be a pig.

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6 hours ago, carlsson said:

In practice you should be able to PRINT PEEK(36879) to tell what it is set to. If it tells you 27, that is cyan except that your TV is tuned to overcompensate colours, making it look blue. If it tells you 30, you really have a blue border, which I strongly doubt is the case.

 

It can be compared with the rare P500 which supposedly should have a cyan border and white background, but on some TV sets and perhaps in combination to how the pots on the motherboard are set, will make it look bright green. Many people have assumed it is green because if it looks like a pig and squeaks like a pig, it must be a pig.

 

Yep, I realize the computer reports the color as being cyan, but it is just not so ;) I previously had three Vic-20's (two are now sold) in which two represented the border color as "really" cyan, and the third represented it as this blue color (although the peed command of course indicates otherwise). I have made every possible pot adjustment to correct it, but nothing will change it. The only thing that actually brings the cyan color back to the border on this particular Vic is to turn the hue on the TV all the way to the left (G) side.For the other "normal" Vic-20's I have had, hue set on the same TV to center (default) produced the normal cyan border.

 

Same TV, same composite cable. It is just that some of these Vic's want to have a blue border for some reason. I'd imagine there is some logical reason for it internally.

 

What is even stranger is that I am looking at the screen (on my screen) and it looks blue, but if I take a picture of it with my phone...the picture is cyan! Maybe its possessed! ;)

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On 12/22/2020 at 5:56 PM, DistantStar001 said:

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?

Ahh, my question too.

 

I've got an NTSC VIC with black screen, so suspecting the VIC chip - I've got spare 6561s but no spare 6560s - I can see a single one on Aliexpress for $46 (yikes) - more than double what the more plentiful 6561s go for (12 sellers when I checked just now).  But reading the thread it looks like I won't be able to convert it to PAL (although it seems possible to go PAL -> NTSC).

 

For the ROMs, I've been replacing mine with 27xxx versions using some 23-to-27 converter boards I got made using SukkoPera's design.  Works a treat and allows me to also install a switchable original/JiffyDOS kernel ROM.  If the ROM is already socketed then I can just put the adaptor board in the socket, or I'll remove the ROM or socket and just solder the adaptor board into the motherboard as I'm never going to put a 23xx back in there.  

 

/Brett

2021-02-17 16.29.15.jpg

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On 12/22/2020 at 5:56 PM, DistantStar001 said:

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)? 

 

I've found Aliexpress to have the best prices - US$15-17 per 6561 ... search for "mos6561" ... but 6560s seem to be around US$40 everywhere I've looked (okay, just ebay and Aliexpress)

 

/Brett

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On 3/27/2021 at 6:57 PM, asdf87 said:

I've got an NTSC VIC with black screen, so suspecting the VIC chip - I've got spare 6561s but no spare 6560s - I can see a single one on Aliexpress for $46 (yikes) - more than double what the more plentiful 6561s go for (12 sellers when I checked just now).  But reading the thread it looks like I won't be able to convert it to PAL (although it seems possible to go PAL -> NTSC).

Unfortunately, you're right.  Only the cost reduced NTSC boards can be converted.  The PAL two-prongs have an additional IC between the video cage and the cartridge port that isn't present on the NTSC.  

 

On 3/27/2021 at 6:57 PM, asdf87 said:

For the ROMs, I've been replacing mine with 27xxx versions using some 23-to-27 converter boards I got made using SukkoPera's design.  Works a treat and allows me to also install a switchable original/JiffyDOS kernel ROM.  If the ROM is already socketed then I can just put the adaptor board in the socket, or I'll remove the ROM or socket and just solder the adaptor board into the motherboard as I'm never going to put a 23xx back in there.  

Sadly, I don't have an ePROM programer, so I'm stuck looking for the original ROMs at the moment.

 

On 3/27/2021 at 11:11 PM, asdf87 said:

I've found Aliexpress to have the best prices - US$15-17 per 6561 ... search for "mos6561" ... but 6560s seem to be around US$40 everywhere I've looked (okay, just ebay and Aliexpress)

Good News on that front.  I found all of these!  It's only the ROMs (and a case) that I need.  Then it's a fully functional VIC-20! 🙂

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On 3/31/2021 at 6:47 AM, DistantStar001 said:

Sadly, I don't have an ePROM programer, so I'm stuck looking for the original ROMs at the moment.

Happy to help out if you're interested (posting from Australia) ... although I've just blown the UV lamp in my eraser because I forgot about it and left it on for several days.  Waiting on a replacement ... 

 

I've been experimenting with adding the C64 character ROM to the VIC - did a short video - weird behaviour at the moment ... the VIC20 ROM results in a two column display and the C64 ROM has a six column display ... ohhhkay ... been fiddling with other stuff so haven't done any investigation into where I went wrong yet ... sticking the original VIC20 character ROM back in works fine.

 

I also replace the LM323 regulator (and heat sink) in the two-prong versions with a PSU5 from ezsbc.com, and am investigating whether replacing the rectifier with a modern version can do away with the massive heat sink it also has (just use a small square heat sink)

 

/Brett

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Posted (edited)

Getting off topic ... this is a two-prong VIC20 where I replaced the LM323 with a PSU7 (not PSU5) from ezsbc.com ... it's higher power but a small drawback is that it won't turn on if the input is above 2V ... this will happen if you switch the VIC off then back on quickly (i.e. changing cartridge) because the big 4700µF smoothing capacitor still has a lot of charge, keeping the input voltage above 2V for some time as it slowly discharges.

 

So my workaround was adding in a push-button with resistor to dump the capacitor's charge quickly.  So I've switched to the PSU5 instead of the PSU7 to avoid this problem.

 

/Brett

2021-02-07 10.25.55.jpg

Edited by asdf87

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On 3/31/2021 at 6:47 AM, DistantStar001 said:

Sadly, I don't have an ePROM programer, so I'm stuck looking for the original ROMs at the moment.

 

Oh, I just remembered another option - getting one or more ROM-el replacements.  For an additional £5 they will program it with whatever ROMs you want.

 

Not sure if you can use it to replace the 2332 for the character ROM though.

 

/Brett

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