repairs for vicist

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mrr19121970
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Re: repairs for vicist

Post by mrr19121970 »

I tried the new version of crosstalk.prg, says:

Code: Select all

blk5 seg0 present.
blk5 seg1 present.
blk5 seg2 present.
blk5 seg3 present.

press space
mod not made. starbattle-a0.prg won't run

update
mod made. starbattle-a0.prg runs!!
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tokra
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Re: repairs for vicist

Post by tokra »

Glad you could get it to run. This means there was crosstalk from memory banks that were not even activated by the dip-switches (as far as I can tell). Either way this shows VR/W is necessary instead of CR/W.
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mrr19121970
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Re: repairs for vicist

Post by mrr19121970 »

Well I only had bank 5 activated. Nothing more.
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e5frog
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Re: repairs for vicist

Post by e5frog »

I've got a VIC-20 that acts up, 9VAC handwarmer version, if BLK0 and BLK5 are activated at the same time I get crosstalk with the test program.

Doesn't matter if I did the VR/W on the Dorktronic RAM, same anyway. With the MegaCart and FE3 I only have crosstalk in one direction.

I think there's a problem with the computer itself, any idea where I should start looking?

I have two more, a year older or so with PET keyboards, with Dorktronic RAM (VR/W modded) I get the same errors six 0 > 5 and six the other way. Not sure it's built to work as 32k+3k...
Both have no crosstalk reported when running FE3 (All RAM) nor MegaCart (32k +3k).

I never tried Dorktronic with the CR/W on the two good (PET keyboard) computers... reversing mod... When running the Dorktronic from CR/W there's even more crosstalk than when running it from VR/W - so even if both are bad it's only between BLK0 and BLK5 when in VR/W mode, when in CR/W there's from other BLK:s as well.
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tokra
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Re: repairs for vicist

Post by tokra »

As Dorktronic's RAM only has 32K it uses the same physical memory for BLK5 and BLK0 if you active BLK0 and BLK5 at the same time and as such you will always get crosstalk there. If there is no other crosstalk then the device is ok. So VR/W instead of CR/W does fix the crosstalk problem between other blocks.
Bobbi
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Re: repairs for vicist

Post by Bobbi »

I have the Dorktronic memory and it is 32K not 35K. If you activate blk 0 and 5 at the same time, the 3k is shared (as stated in the docs.)

I have some memory testing assembler code which can detect and report crosstalk, if anyone wants it. I used it to test this memory when I first received it. I was going to clean it up and release it, but never got around to it.
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e5frog
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Re: repairs for vicist

Post by e5frog »

The same computer acts up with FE3 and MegaCart as well when in "Full RAM" or 32k+3k mode, so even though Dorktronic is free from guilt there seems to be a problem with that computer there's BLKx > BLK0 errors on both of them one per BLK on MegaCart and two or three with the FE3. I also get occasional characters on mostly middle of screen, even when standing idle with just a BASIC listing on screen and doing nothing.

As mentioned elsewhere I tried swapping all socketed chips between this and another machine (that has none of these errors), didn't help.
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e5frog
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Re: repairs for vicist

Post by e5frog »

I have been swapping soldered chips on my quirky computer.

Resoldered the cartridge port, remove old solder and resoldered - no change.
The '245:s at UD8, UE8 and UF8 had been swapped recently, don't remember if it was me so I just resoldered those - no change.
Reseated and check sockets of VIC chip and CPU - no change.
Swapped '138 at UC6, UC5 and UC4, I only had HCT138, tested after each chip but no difference, still about the same amount of errors in the same places.

About here I checked the difference between this REV D. board and the working REV C. Board, main things that differ is different kind of decoupling caps (looks like glass diodes on the older board) RAM is 2114P-3 on old one but 2114LP-3 on the newer quirky one - I think LP means low power I haven't checked the datasheet though. There's also one trace from the cartridge port that is drawn under the 7406 UB10 instead of outside like on the older board, CA13 as far as I can see.

After swapping the LS02 at UC3 I was also thinking if the frequency adjustment mattered. I got just one crosstalk error after swapping the LS02 at UC3 and after playing a little with the frequency adjustment (C35 I think it's called) I didn't get any errors at all.

If you want to measure the frequency with a meter, which is a good pin to hook up the meter to?

Maybe the crosstalk is because the VIC is out of tune, maybe it was a combination with a glitchy chip or bad solder joint...

Computer assembled, still no errors with MegaCart.
I do get some errors with FE3 though - back to MegaCart, no errors, so maybe some more tuning, perhaps there's a sweet spot where both works.

EDIT:
Hooked frequency meter to PHI2 on VIC and adjusted to double color burst for PAL, it was a bit high.
Looks good with MegaCart on this odd computer, the FE3 still reports crosstalk errors though, I'm not in an experimental mood at the moment, so I'll leave it for now.

EDIT again.
I can actually play DOOM on this computer now with MegaCart - yay!
But on this particular VIC it doesn't work with the FE3... so why not try the VR/W mod...
EDIT some more.
If changing from CR/W to VR/W on the FE3 it stops working, just boots up to plain unexpanded screen. As the SD2IEC is a separate device I'm sure it works just fine though - so, not recommended.
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