Denial

This is 'bus number 3'. Sadly, even though I asked the seller to make sure they packed well this happened....

3 keys off (thankfully not damaged, just knocked/rattled off) and 2 severe cracks in the upper case (3/6 rear hooks too)
Also, was working before sending. 1st turn on for me was about 6 seconds black screen followed by:
Then I tried reseating VIC-I and now only black screen.

Case has no serial number sticker on it. Mainboard has serial number 011777

VIA1 2581
VIA2 2581
VIC1 3681
CHAR 1781
MPU 3481
BASIC 2181
KERNAL 1981

ouch! tha thurts!

That has happened to me a couple of times. The sellers just put everything in a box and send by mail. The transformator banging the keyboard from all directions broked a few keys a couple of times.

Sorry to see that happening to our babies

Well this one was only the VC20, he didn't send me the transformer. Makes me wonder how it sold as "fully functional" (clearly it is not working). The VC20 was sent in a 45,0 x 35,0 x 20,0cm box with 1 or 2 layers of bubble wrap and then crumpled newspaper ontop.

On a side note, anyone feel they can 'guess the serial number' based on the IC date codes and board serial number? My assumption based on this, is that it is a WGA model. The IC date codes and board serial number suggest much less than WGA12033.

1st power on. Anyone seen this one before?
Now only black screen (flickers on power off/power on)

So I tried the usual suspects VIC-I, KERNAL in another machine OK. Removed VIA1 & VIA2 (no improvement). Reseated MPU, CHAR, BASIC (no improvement).

Next ??

http://personalpages.tds.net/~rcarlsen/ ... /vic20.txt

UD8 and UE8 MPS65245 or MOS65245 or 74LS245 TRI-STATE LOGIC
Blank screen. Partical failure: garbled video or audio. see UB7

I sometimes get that screen when plugging in my Super Expander cart.

I have to wiggle and jiggle it about a bit to get it to work (while switched off of course).

If this gives you any clues as to what is wrong, I might be able to work out what is happening when I plug in the cart too.

Sadly this screen was only a one off. Now only black screen of death. I bought the machine as fully tested and working on a platform with no buyer protection. Yeah. I am bad. The seller says it was working and not smashed when they sent it and told me to deal with the courier / insurance. So on this basis I am not willing to touch the machine just now.

I am still keen on knowing what the serial number should/could be. It is definitely a a WGA by the mainboard ASSY.

mrr19121970 wrote:Sadly this screen was only a one off. Now only black screen of death. I bought the machine as fully tested and working on a platform with no buyer protection. Yeah. I am bad. The seller says it was working and not smashed when they sent it and told me to deal with the courier / insurance. So on this basis I am not willing to touch the machine just now.

I am still keen on knowing what the serial number should/could be. It is definitely a a WGA by the mainboard ASSY.

The first screen you saw is what you get when the address bus or databus get garbaged. Since you even had a picture, both 6502 and kernal was working (memory test is the first thing before the display is shown). So I would suspect the 74LS245 buffers or a poor clk. You have a scope?

Serial & mainboard number would be the same if none of the boards were rejected during testing, so its certainly with a lower WGA serial than whats on the mainboard.

Well I was also thinking 6502 as well, but in my experience a dead 6502 is dead (no flicker with on off). But I am open to all suggestions, just not in the mood to touch this baby. I feel cheated by the seller.

I was hoping jogi would throw some light on the possible serial number. Basically he said the mainboards were randomly in a big box and put into cases. There is little correlation between mainboard and case serial. I only got confirmation from him it is a WGA (which I already knew). I was hoping he would say base on those ic data codes the serial is probably xxxx-yyyy (I am assuming 4 digit).

But adding the mainboard serial number to the "replica" serial case badge suits me well to.

I don't have and 245 glue. Will order now. I have a USB scope for my pc. Don't really know how to use it.

All major ICs (socketed) VIA1, VIA2, VIC-I, CHAR, MPU, BASIC & KERNAL all fine and running in another machine now on the test harness. Leaves only glue and RAM. Ordered 5x 245s

Update

How could this happen ? Are the chips so sensitive that they could be damaged by a knock or drop at the same time the case damage occurred??

mrr19121970 wrote:How could this happen ? Are the chips so sensitive that they could be damaged by a knock or drop at the same time the case damage occurred??

No

However, the symptoms you had at 1st that before getting your screen full of garbage, you had a black screen for 6 seconds indicate a high likelihood that there is a significant problem with the reset architecture (the 555 and surrounding components) and more than likely the main timing capacitor is dead.

Also, damage to RAM is quite frequent.

If this malfunction is the result of severe shock during transport, there could be damage to traces on the board. Very tedious work to investigate and fix.

Capacitors might have suffered excessive Gs and suffered internal damage as well.

This might indicate that there's a problem with the 3k extra ram on board my Super expander cart.

mrr19121970 wrote:I don't have and 245 glue. Will order now. I have a USB scope for my pc. Don't really know how to use it.

Well, there is a ground connector to most Picoscopes and the needle/proble/wire would be the signal wire. Connect the ground to GND on one of the ports and use the needle/probel/wire to see that you have a 1MHz square-ish wave signal on one of the CLK pins of the 6502. It should oscillate between 0 and about +5V. If there is no CLK signal on the 6502, I would suspect the clock circuit (capacitors, crystal++). If there is a clock, try doing a manual reset and/or desolder the 555. If its not that, then the SRAM is probably not doing too well. Socket the SRAM and try other chips. If its not that either then replace the 245s.

Some Vic-20 boards have very poor soldering, especially the early ones with PET keyboards. You can search for poor solders and try to resolder them (easy enough). Maybe you are lucky..

Well this is what I see on

CLK IN PIN37
CLK1 OUT PIN3
CLK2 OUT PIN39

Well I just received a 100% refund for this machine including postage costs. I guess soon I will have the soldering iron out on those UD8, UE8 & UF8 logic chips. I have also been collecting bits of ABS to perform ABS weld/stitching on the inside of the case. A friend with a 3D printer has made me some prototype 'case hooks' too.