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That worked. Thank you!

I was able to order a Combodevice so I guess I'll be installing a new bootloader ROM.

True, it's purely a boot loader and not a BIOS. I can't think of any other home computer without a BIOS. Maybe a very early home PC like the Altair 8080. I don't know if those things even had a boot...

The keyboard circuit board has "33 11 89" written on it with black ink. and "7 103 541" etched onto the circuit board.

I think the manual has some warranty information in the back. It appears to...

At first I was skeptical of a a 512 byte BIOS, but it's actually very convenient. I don't have to type any commands from BASIC to load a game. The keyboard is very nice too, it has a very soft touch....

I think the next thing I should do is try to get a Combodevice, if I can't then there's no reason to replace the ROM. I actually like the existing boot loader. You don't have to type in a command to...

Thanks. The modification looks easy enough to do own my own, although the adapter certainly would be tidier. Is there a reason to load multiple BIOSes? Or do you put something else in the extra ROM...

I have blank 27256 and 27512, I can use either.

D9 is a PT5, the 512 byte ROM. Are there instructions on how to upgrade this to a larger ROM? Since it uses two Chip Select lines I'm not sure if I could directly replace it with a 27256? I'd...

It looks like it found two more bad RAMs. D78 and D64?

https://hosting.photobucket.com/images/i/cyb2600/IMG_2726.jpg

Same result with second utility
...

Success! It now boots, but the colors seem inverted. The background is yellow and the lines are blue. I'll try connecting the resistors directly to the inverters as in the schematic, but last time I...

With the logic analyzer I could see it writing 01010101 and 10101010 to bank 3 of the RAM, but it was reading back 01011101 10101010 - bit 5 is stuck high, that RAM chip must be bad. At least this...

I see. No, I don't see any deformed traces. I looked the board over on both sides, the only unusual thing I saw was a cut trace on the top side. It looks like it was deliberately cut, though, not an...

Ah, I misunderstood. I checked the pins, none of them were bent over or touching traces.

I also have these manuals and tapes. They appear to be BASIC and Assembly manuals.https://hosting.photobucket.com/images/i/cyb2600/IMG_2690.jpg

Thank you! I think I see in the schematic where to grab those signals, I'll test.

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I attached 3 data probes to a13-a15 and one to wr to see if the computer was trying...

Ah, that makes sense. I tried again plugged into pin 3 and it was the same behavior unfortunately.

Maybe I connected to tape out instead of tape in? I used pin 1, with pin 2 for ground.

This computer came with a schematic and a couple tapes. The schematic looks identical to the ones on the...

I cleaned all three areas up with rubbing alcohol until they were shiny, and I verified none of the traces were broken from corrosion. Unfortunately it didn't make any difference.

Thank you. This is what I see on pin 15 of the RAMs. I don't think that's right!
https://hosting.photobucket.com/images/i/cyb2600/IMG_2679.jpg

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The blue wires are my...

Does anybody have the pinout for the р565ру6 RAM? I'm seeing some very strange signals on pins 14 and 13. I think everyone is right about the capacitors being bad.

I powered on the Vector and see the checkerboard and hear buzzing and "rus" light is on.

I pressed "VVOD" and "BLK" simultaneously. The screen goes black, the "rus" light turns off, the buzzing...

The serial number does end in 89-3. The computer does nothing but buzz until the reset buttons are pressed. The ROM seems to have 4 chip selects, two active high and two active low. The two "active...

The reset line is low, it goes high for a second when I press the reset buttons. I see activity on the data and address busses but I haven't yet verified it's the same on the CPU as the ROM. I...

I'll look at the sync with the oscilloscope when it happens again. 80% of the time I get a stable picture, where the screen turns black when I hit the reset buttons and the buzzer stops. 20% of the...

I do have an oscilloscope and a logic analyzer. Originally the flip flop triggering the ROM chip select was stuck between levels so I replaced it. I haven't checked the capacitors but the power...