Help with WHITE screen issue

[Linzino]

I have just aquired a Commodore VC 20 (PAL for the German market).
(No "I" in the name because it was meant for that German market and VIC would have sounded like an F-word).
The first time I powered this poor VC 20, it, sort of, started with random characters but froze soon after.
Now if I turn it on I get a WHITE (not black) screen with no borders.
The SD2IEC lights up but no blind commands produce any effects.
No blind commands produce any sound.
The VIC (6561) and Kernal (901486-07) are the only socketed chips and both work because I have tested them.
I can not feel any special heat on any chip.
The rest looks in a not so bad condition despite the age.

Which chips or which components are the most likely causes of this white screen issue?

Any help is welcome!

Thanks in advance!

Linzino

[rgrocha]

I'd tell you to follow Ray Carlsen's superb guide to repair ours VIC-20, at http://personalpages.tds.net/~rcarlsen/ ... /vic20.txt

Regards,
R

[mrr19121970]

Did you also try cartridges (Avenger). Do you have a user port reset? What happens when you press it? Does the SD2IEC also get the reset signal? Are you using a SaV64 or Ray Carlsen PSU (assuming you have a 5v DB/9v AC model)

You have a 2nd (working VIC) to test? If not, then you are really in problems. If you do, then use the link that @rgrocha mentioned. Start with the obvious chips & desolder them from your broken VIC and test them 1 by one in your working one.

VIC-1
VIA1

[Linzino]

Hi

Yes, I have the common Vic 20 (actually a German VC 20) with the common PSU.
I do have a second Vic 20 whose Vic and Kernal have been used to try to fix and test the malfunctioning VC 20.
All other chips are socketed included the CPU
Substituting the Vic and Kernal did not fix the white screen issue.

My SD2IEC gets reset ONLY when I turn the VC 20 on. If I reset it (using the reset button of my Behr Bonz)
the SD2IEC is not reset. No blind disk or sound commands work.

I can tell for sure that the issue is not a blank/black screen because I can clearly see a blank/black screen when I remove the kernal.
I get a uniform WHITE screen after about 3-4 seconds from power on.

If I follow Ray Carlsen guide, the only possible culprit is the 7402, which is socketed.

I would like to pin down a small set of possible chips.

Any advice on how to desolder the chips is welcome considering I have close to zero experience with a soldering iron.

Thanks for any help!

[mrr19121970]

See here

http://personalpages.tds.net/~rcarlsen/ ... solder.txt

The button on behr bonz is not a reset switch. It is a return to menu. I don't know of this will send a rest signal to the serial. Eslapion must confirm.

Also you are writing the chips are socketed. Can you please.post pics. If they are socked then you pull them out and you are asking about desoldering. I will post a pic of a soldered chip, socket and socketed chip for reference.

[joshuadenmark]

If You have no soldering skills you'll need help, these old boards are fragile and its so easy to break.

[mrr19121970]

I do have a second Vic 20 whose Vic and Kernal have been used to try to fix and test the malfunctioning VC 20.
All other chips are socketed included the CPU
Substituting the Vic and Kernal did not fix the white screen issue.

You need to take the working VIC20 as the reference. Remove 1 socketed chip at a time, take the chip from the broken VIC20 and test. You can mark the chips good/bad. You should not test good chips in a broken board, this doesn't prove anything.

See my pics, I even go 1 step further and make labels for all chips (UE10) and put them all in place. This way I also have a reference where It came from, I write BAD on this label & OK when tested.

You should find someone nearby who has good soldering skills and tools, maybe there is a retro club or meeting near to where you live? They can assist you.

[Linzino]

Thanks everyone for your replies!
Yes, of course, I have a working VIC 20, which I have used as a reference.
On the malfunctiong VC 20 I have substituted ALL socketed chips (VIC1 and Kernal) with 100% working ones.
In particular I am sure that both the VIC1 and the Kernal are OK!
Maybe the sockets of the VIC1 and Kernal are broken (which is unlikely) but I am sure that the chips are fine because I have tested them.
ALL other chips are soldered and required desoldering.

Once I get hold of some desoldering tools I will probably start with the 7402 (UB9).
Any advice on the desoldering tools? Would a cheap soldering iron and a copper braid do?

[mrr19121970]

On the malfunctiong VC 20 I have substituted ALL socketed chips (VIC1 and Kernal) with 100% working ones.

This is wrong. Test the chips from the dead machine in the working machine. You seem to be doing this the other way around.

In particular I am sure that both the VIC1 and the Kernal are OK!

How do you know this?

Maybe the sockets of the VIC1 and Kernal are broken (which is unlikely)

Actually this happens more often than you might think. You can test this easily, take a hook probe and connect it to PIN1 of the chip you want to test and with the continuity setting of your multimeter touch the other probe against the back of the mainboard. It should beep. now repeat for all pins. This week I had 4 legs broken on a socket.

Any advice on the desoldering tools? Would a cheap soldering iron and a copper braid do?

This is a matter of taste, but I would say don't use a cheap soldering iron. Use a temperature controlled model. A solder sucker is probably better than braid - but again this is again down to personal preference. See here

Don't forget the article I mentioned REPLACING IC "CHIPS" IN COMMODORE EQUIPMENT

I also sent you a PM, check your inbox.

[r.cade]

With no repair experience, my advice would be to send it to someone for repair or trade-in on a working one.

[mrr19121970]

If there is someone locally based, then this is ideal. If not, I have offered to help for the return postage and cost of sockets.

[Linzino]

Hi,

As far as the VIC1 and Kernal are concerned, I am sure they are not the issue because I have removed and tested them on
a working VIC20.
I have used the VIC1 and Kernal from the working VIC20 on the broken VC20, (as well as a working fully working Multi Kernal).
The VIC1 from the working VIC20 is now in the broken VC20, which is still producing a white screen.
The VIC1 from the broken is in the working VIC20, which is working fine.

Before even thinking about how to desolder I am going to remove the VIC1 and Kernal again and see
if I can clean the sockets with an anti-oxidation spray.
Before I start with the desoldering I will either try to find someone more experienced or find some decent equipment.
Ideally, I would like to learn how to solder/desolder because I have several vintage computers that need some repair.

[mrr19121970]

This is the best way. Go for it....

[Linzino]

Is M53202P the standard name for the 7402 (MASTER CLOCK OSC) chip?

I found the MASTER CLOCK OSC in Aliexpress but delivery from China takes ages.
Therefore I am considering other options.

Could anyone recommend any other shop?
My choice was for
http://store.retroleum.co.uk/ only has C64 and ZX Spectrum parts.

[mrr19121970]

eBay

2 Pieces 5 euro incl post

but better removing this from the white screen VIC and inserting it in the working one. You should get white screen now? Try working 7402 in dead VIC