Help fixing Vector-06c

Hello,

First off my apologies, I'm in the USA and I only speak English.

A long time ago I bought a BK-0010 and a Vector-06c off of Ebay. The BK-0010 works fine but the Vector has lots of problems. I've already replaced the CPU and two flipflop chips so at least it boots, but now I'm stuck.
https://hosting.photobucket.com/imag...0/IMG_2667.jpg

As you can see the colors are very washed out. I followed svofski's modifications to get a good sync signal, but when I tried to wire resistors R16-R29 directly to the inverter I only get a white screen. So I reverted it.

https://hosting.photobucket.com/imag...0/IMG_2669.jpg

When I turn on the computer I hear a buzzing noise, the "rus" LED is on, and I see this checker pattern on the screen. When I hit "vvod" and "blk" the screen goes blank, the LED turns off, and the buzzing stops. I also hear a "click" noise.
https://hosting.photobucket.com/imag...0/IMG_2670.jpg

I hooked the cassette port up to my PC and played back a wav file. I can hear it on the Vector-06c's speaker but nothing else happens.

I'm not sure what to check next. I think the computer is running but it won't load a program and I can't get a good picture out of it. Any help would be greatly appreciated. Thank you!

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Сообщение от cyb2600

Hello,
First off my apologies, I'm in the USA and I only speak English.
A long time ago I bought a BK-0010 and a Vector-06c off of Ebay. The BK-0010 works fine but the Vector has lots of problems. I've already replaced the CPU and two flipflop chips so at least it boots, but now I'm stuck.
...

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Hello.
I am writing through an online translator.
The checkered picture when turned on is a good sign.

If the boot grid does not appear, the memory may be defective.

Can I find the serial number and release date of this computer?
A relay seems to be installed near the speaker, this is an exceptional rarity.

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Сообщение от KTSerg

Hello.
I am writing through an online translator.
The checkered picture when turned on is a good sign.

If the boot grid does not appear, the memory may be defective.

Can I find the serial number and release date of this computer?
A relay seems to be installed near the speaker, this is an exceptional rarity.

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Yes, the sticker on the back says "00706 12 89". I noticed this motherboard is slightly different than the pictures I saw. For instance r30 is missing. Also the keyboard has real switches.

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Сообщение от cyb2600

Yes, the sticker on the back says "00706 12 89". ...

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Thank.

Please look carefully at the tracks, from the underside, around the board mounting holes. They are often squashed and short-circuited.

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Сообщение от KTSerg

The checkered picture when turned on is a good sign.
If the boot grid does not appear, the memory may be defective.

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But the pattern in the original poster's screenshot does not look like a boot grid at all.
Here's a proper "boot grid" (barring the text at the top that could be different depending on the bootloader ROM version and the filled blocks that only appear when the bootloader is loading byte blocks from the cassette tape):

https://lh3.googleusercontent.com/pr...3yUFrDCBTytOoc

Even putting the issue with washed colors aside, the first picture does not look like the bootloader has properly started. And the second pic rather looks like there's an issue with h/vsync (which is actually quite possible since Vector-06c has known issues with its video output not being 100% conformant to the standards. Old Soviet TVs did tolerate this, but it's not necessarily true with CRT monitors like the NEC you have)

I did find a dead bug in the case but I removed it. There's some rust on a few chips, but other than that everything looks okay. I've been removing the chips and testing them, one by one. So far I've found three bad ones. I think I might just have to keep replacing chips until I find all the bad ones. The circuit board has "556-04-89-3" written on it.

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Сообщение от cyb2600

I did find a dead bug in the case but I removed it. There's some rust on a few chips, but other than that everything looks okay. I've been removing the chips and testing them, one by one. So far I've found three bad ones. I think I might just have to keep replacing chips until I find all the bad ones. The circuit board has "556-04-89-3" written on it.

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It could be not only the chips. I'd suggest you tested that the motherboard gets clean power (all the required voltages and polarities), and if there are polar capacitors on the motherboard, I would replace them since some Soviet capacitors were known to loose their capacity over time.

If that does not help, you'd need an oscilloscope / logic analyzer to figure out if what's going on (e.g. if the CPU reads data from ROM and not RAM on cold boot - this is controlled by a flip-flop wired to the three keyboard buttons in the upper right)

Perhaps I need to elaborate on the last sentence a little bit: Vector-06c uses a primitive ROM shadowing technique. On cold boot / after hard reset the motherboard gets initialized in a way that the CPU reads data from the on-board ROM but writes data to the RAM. And there's a flip-flop that can be switched either manually by simultaneously pressing the two rightmost buttons in the upper right, or (in later revisions of the motherboard and the bootloader) programmatically by the bootloader firmware). Once the switch did happen, the bootloader ROM is no longer accessible unless the next hard reset.

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 levels are all good.

Strangely, sometimes when I turn it on I get a different behavior. The screen rolls no matter how I adjust the brightness and contrast. When I press the reset buttons, the checkerboard turns purple and then is replaced by vertical lines. The buzzing does not stop and the "rus" LED does not turn off. This happens randomly, I can't find any pattern. I think my next step should be to replace all the capacitors.

I don't know how to upload a video here but here are two screenshots of what happens. https://hosting.photobucket.com/imag...0/IMG_2673.PNG https://hosting.photobucket.com/imag...0/IMG_2674.PNG

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Сообщение от cyb2600

The screen rolls no matter how I adjust the brightness and contrast.

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This, as well as horizontal distortion I can see in your pics speaks about your NEC not picking horizontal / vertical sync properly.
Does the video signal look right if you hook up an oscilloscope to the video output?

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Also, take a look at this wiring diagram, especially capacitor marked as C33 on the right:
https://i.imgur.com/d1XlPX6.jpg

Even if the original capacitor is healthy, it's capacity is insufficient and it distorts the video signal.
So you might want to hook an additional capacitor in parallel as suggested in the wiring diagram.

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 time I get the rolling picture and it doesn't respond to the resets.

This is what the composite sync looks like when I have a stable picture.
https://hosting.photobucket.com/imag...0/IMG_2676.jpg

Edit: Yes, I added a 220uf electrolytic capacitor across C33. I made every modification in that circuit diagram except for wiring the resistors directly to the inverter. When I did that I only get a solid white screen.

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Сообщение от x-code

Perhaps I need to elaborate on the last sentence a little bit: Vector-06c uses a primitive ROM shadowing technique. On cold boot / after hard reset the motherboard gets initialized in a way that the CPU reads data from the on-board ROM but writes data to the RAM. And there's a flip-flop that can be switched either manually by simultaneously pressing the two rightmost buttons in the upper right, or (in later revisions of the motherboard and the bootloader) programmatically by the bootloader firmware). Once the switch did happen, the bootloader ROM is no longer accessible unless the next hard reset.

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When I boot the computer up, all 4 chip selects on the ROM are high. When I press the reset buttons, I see continuous data on the two inverted chip select inputs. Should they go high again after the boot ROM is copied to RAM?