VECTREX WITH PROBLEMS

[daver2]

There be glitches there!

Can you scope pins 4 and 8 of IC305 to see what is going in to that IC please.

Dave

 

[bsb]

It probably can be repaired--there's an image. As to what the exact problem might be--it could be something as simple as a bad pot, or considerably more involve.

Good evening guys,
I'm about to buy a vectrex console that has a defect in the screen (as in the photo)...
do you think it can be repaired? It appears that the image is shifted all the way to the right and is compressed ...
Thanks so much!

Congrats! I still have the one I bought new, in the box. I picked it up on clearance after Vectrex went out of business and grabbed the light pen, and a lot of games. Sadly some parts got lost over the years, but it still works and I still have the games in their boxes with their screen cards. Fun machine.

I am routing for you to figure this out. Good luck!

 

[Desperado]

IC305 PIN 4:

IC305 PIN8:

 

[daver2]

They look Ok.

Could you scope pin 5 to see what is going on there as well please.

I am going out now for the rest of the evening, so I will have a think tomorrow about where we go next (based on what I see in your video of course).

Dave

 

[Desperado]

They look Ok.

Could you scope pin 5 to see what is going on there as well please.

I am going out now for the rest of the evening, so I will have a think tomorrow about where we go next (based on what I see in your video of course).

Dave

Ok have a nice evening!
This is scope on IC305 pin 5:

 

[daver2]

If there is no flux residue on the solder side of the PCB around the pins of IC305 I am suspecting IC305 is in need of replacement.

All of the signals going into the IC switch are clean, but what is coming out is noisy. The two (2) outputs from IC305 (on pins 3 and 9) go through 2 off 10k resistors, so there shouldn’t be any ‘noise’ or ‘glitches’ feeding backwards from the OPAMPS.

That’s my best guess anyhow.

Dave

 

[Desperado]

If there is no flux residue on the solder side of the PCB around the pins of IC305 I am suspecting IC305 is in need of replacement.

All of the signals going into the IC switch are clean, but what is coming out is noisy. The two (2) outputs from IC305 (on pins 3 and 9) go through 2 off 10k resistors, so there shouldn’t be any ‘noise’ or ‘glitches’ feeding backwards from the OPAMPS.

That’s my best guess anyhow.

Dave

Good morning Dave,
can i found this ic on a old Commodore maybe?
Thanks and have a nice day

 

[daver2]

Have a look, but I wouldn’t think so.

They are still in production. Mouser have them available at 50 pence each. I am sure you can find some in Italy. Look for a CD4066B.

Dave

 

[Desperado]

Good evening Dave, i removed ic305 from pcb....please can be fine one of these ic founded on old c64 board?Thanks!

 

[Desperado]

Dave i'm desperate
I Removed Ic305 from board, i socketed and i inserted MC14066BCP ic but i have always same bad flickering screen on vectrex

 

[Desperado]

I have flickering screen but i can't see glitches with scope!

 

[daver2]

Is it possible that the glitches are/were in some way a result of how you were taking the measurements on that Vectrex machine I wonder?

You were using the same ‘ground’ reference for the oscilloscope probe?

The other possibility is that by changing the IC we have fixed another (but unrelated) fault we didn’t know we had?!

Either way, I would propose next that you read up the service manual on how to adjust the potentiometers using the diagnostic cartridge - and proceed like that.

In the meantime, I’ll have a think...

Dave

 

[Desperado]

The other possibility is that by changing the IC we have fixed another (but unrelated) fault we didn’t know we had?!

Hi Dave, yes i think this..... before changing the old IC i had always glitches and now not!

Can i try adjust Dac 0v with this tutorial?

 

[Desperado]

In my pcb the correct pin for measure of DAC is IC304 pin6 and not pin1.....i set to 0v but i have always flickering screen...i think that i have other bad ic or component

 

[Desperado]

Great news Dave!
I tried to make various adjustments with the diagnostic cartridge, and then tried swapping IC301 (MC1408) with the other Vectrex and i immediately saw that the screen was no longer shaking but just had to be adjusted.
I adjusted the various potentiometers with the help of the cartridge and I finally got a working console!
Now I have ordered another spare that I stole from the other Vectrex, then we can start fixing that too
I thank you again for the precious help you gave me, I hope you can help me for the other too ...
Have a good evening sir!

 

[Gary C]

Yay

Dave is a bit of a star isn't he

 

[Chuck(G)]

Hats off for staying with this for 355 posts! I did warn way at the beginning that old CMOS ICs did appear to fail more frequently than one would expect. It could be that the process wasn't mature enough, but I've certainly run into my share.

 

[Desperado]

Hats off for staying with this for 355 posts! I did warn way at the beginning that old CMOS ICs did appear to fail more frequently than one would expect. It could be that the process wasn't mature enough, but I've certainly run into my share.

it takes a lot of patience and Dave has a lot of patience with me
Thanks at all

 

[daver2]

Well done that man!

Sorry, I have been somewhat busy today with other things. Yesterday I was ‘supervising’ a theatre company putting on a musical presentation for the kids. And, of course, some of the jokes were for the adults that would have gone over the kids’ heads! Anyhow, with setting up, and then tearing down the set; then helping set-up for the Jubilee Tea this afternoon I was bushwhacked, so I had an afternoon siesta! I was planning to do some work on the PDP-8, but only got as far as getting my tools out ...

Anyhow, I couldn’t quite understand what you were saying in posts #350 and #351, so I was going to ask that you post a video of the screen and remeasure IC305 pins 4 and 8 so that I could see what was going on. IC305 pin 8 comes from the ADC (IC301) but after the current to voltage converter op amp.

If the glitches had gone, that meant that replacing IC305 fixed that issue.

What I then would have been looking for was stability of the ADC output on IC305 pin 8. Any instability of the ADC should have been revealed here.

Any instability should have been revealed in the X, Y and Z axes of the monitor. It would have also been manifest in other ways (ADC comparison op amp and the audio output via the DAC).

The usual failure mode of a DAC (apart from a complete failure) would be the loss of one (or more) ‘bits’, resulting in a discontinuous digital to analogue signal. Unfortunately, the diagnostic cartridge doesn’t appear to cater for easily detecting this type of failure.

Just a suggestion, if you are planning on repairing more machines, could I suggest investing in a better oscilloscope?

Anyhow, nice to see it working (and that you have cleaned the dust off the machine)!

I have posted some suggestions on your new thread for the other machine (after installing the replacement DAC).

Dave

 

[Desperado]

Good evening Dave, you're very busy man eheh
If I may ask, what is your job?

Yes i wanna buy a better scope soon, i read your post in the other thread and
as soon as it arrives new ic i'll i will start the work, many thanks!
Have a good night sir!