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VECTREX WITH PROBLEMS

Very interesting...

Can you do the same for the three pins of the other potentiometer please (R333)?

Dave
 
Either you have lost the +5V ANA from one side of both potentiometers, the circuit of your card is different to that in the service manual we have or there is something still wrong with the measurement technique.

Because both potentiometers appear to read the same (one is on the X side and the other is on the Y side), and the Y size works - this is unlikely to be your problem (unfortunately).

We need to find the correct service manual I am afraid.

I have found some of the resistors and capacitors on your board I was looking for though. Not all of the components are actually marked on the silk screen!

Dave
 
I will have a look at that one after work (the website is blocked).

Just out of interest, where was your 0V reference taken from when you were probing the two potentiometers?

One side of each potentiometer should be connected to +5V (ANA) and the other end should be connected to -5V (ANA). If this is not the case, then there may be some PCB issue somewhere. However, the IC power supply for the analogue section of the Vectrex is fed from the +/- 5V (ANA) rails - so they must be there if the Y-axis is working OK.

It could be possible that there is a broken track somewhere on the bottom of the PCB - but this can only have become damaged (realistically) by some mechanical means or a short circuit (high current) damaging the track. I can't imagine either scenario (unless someone has tried to fix it prior to you obtaining the machine).

On the power board there is a width control. Have you tried adjusting this out of interest? Again, note the position BEFORE you start to twiddle - and put it back at the same position afterwards. Note what happens on the display.

Dave
 
Just out of interest, where was your 0V reference taken from when you were probing the two potentiometers?
Hi Dave, i taken 0V ref. from this point in picture!
Where i can find width control?? Thanks!!
 

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I take it that you are referring to the large braided cable?

You have to read the Service Manual I am afraid from cover to cover...

What I referred to as the width control is actually called "X SIZE". You will find it on the power board schematic on page 30 of the Service Manual. It is identified as component R401.

Next, look at the power board layout on page 14 of the Service Manual and identify R401. This is where the control should be located.

You should do this for all of the adjustable things - potentiometers, links etc.

However, in this case, we are not 100% convinced that the Service Manual fully agrees with your particular revision of the PCB. So, it is more important to do a bit of "up front detective work" to work out where things are.

As I mentioned in a previous post, components may actually be present - but not identified on the silk screen layout. So, some more detective work is required.

I only have access to the Service Manual online. I have no Vectrex machine to look at...

Dave
 
I tryied to turn R401 and i can see image slide to the centre but always compressed size! :(
 
Ehy Dave, i ask for the pcb in a facebook vectrex fans group and a boy wrote me this:

"Davide Colombo R333 is one of the pots on the side of the PCB (with a thumb wheel attached), used to align vectors\text. R334 is in the row of resistors right next to the integrators caps. You can't see the 'R334' printed on the PCB, as it's hidden under the resistor itself."
 
He is correct... I found the two resistors I was looking for. Neither of them are marked on the silk screen (well, not when the components are in the board at least) but they are marked on the PCB layout in the Service Manual. This is why I am saying that you need to look at the component identifiers in the Service Manual and compare them to locations on your physical PCB.

The markings on the components should also align with the value of the component taken from the schematic as a cross check.

OK, so the R401 control is actually doing something.

Any chance of taking a small video - or can you describe more accurately what is going on as you turn R401?

Is the whole image moving left and right - or is it also widening and shrinking - or is it just widening and shrinking (and that is what makes you think the image is sliding to the centre)?

Do you observe the image going into the left-hand side of the screen at all?

Getting objective data is never going to fix anything - we are trying to locate some data points...

Dave
 
Good evening Dave, maybe possible use logic probe to found some wrong signals?
 
Unfortunately, there is nothing wrong with the logic signals. These are working correctly to get the display you have already got.

The problems you have are associated with the analogue circuitry. The entire display system within the Vectrex, from the DAC onwards, is analogue.

As a result, your logic probe is no use and you will have to use your oscilloscope to fault find.

What you need to do is to ‘chase’ the analogue signal chain through - comparing the results obtained between the X and Y axis circuitry looking for differences in the traces.

This involves identifying points on the schematic - but you will have to find them on the board yourself.

Dave
 
That is very useful!

However, this waveform will be obtained when only a certain program is running in the Vectrex. There is a “diagnostic/test” cartridge - which I assume you don’t have?

Under what conditions were those traces taken? If you have the necessary firmware they will be really helpful!

Dave
 
That is very useful!

However, this waveform will be obtained when only a certain program is running in the Vectrex. There is a “diagnostic/test” cartridge - which I assume you don’t have?

Under what conditions were those traces taken? If you have the necessary firmware they will be really helpful!

Dave
Yes Dave, unfortunately i don't have this diagnostic cart...but maybe it's possible create one....if i found correct firmware....
On ebay i ve found this:
 
Yep, that’s the diagnostic cartridge with the crosshatch pattern running.

That will flush out your problems!

I may have a copy of the diagnostic code somewhere. I did find it on the internet originally.

Dave
 
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