Just got myself a commodore pet setup but not working

[ajgriff]

Originally Posted by pudwink

Hi
Yes glow from the back of the tube.

..... confirming that power is reaching the monitor.

Alan

[SiriusHardware]

Hi Gents, sorry I have been kept busy all evening. Just quickly looked through Pud's scope captures and they look OK to me and suggest that we may have a monitor fault rather than a computer fault. Bit late for me to go into detail but I think it would be worth powering off and unplugging and reconnecting the monitor signal connector at the monitor pcb end in case it is just hanging half way off.

[SiriusHardware]

Thanks again to AJ for making it easier to find the relevant information.

Pud, first thing to do is get the monitor into a situation where you can easily work on it with it connected to the computer, you need to get it into a state where you can have it running but make measurements from various places on the monitor PCB.

Carry out a careful visual examination of the monitor PCB, on the top side looking for anything unusual (burnt components etc) and on the underside looking for cracked solder joints around component pins, especially the pins of heavy components which are secured to the PCB only by solder, such as the Line Output Transformer and signal transformer T711, the pins of components which heat up and cool down, such as transistor Q721, and the pins of any plug in connectors which may have been removed and inserted many times over the years, such as the video input connector. If you are lucky you may just have a physical fault.

If you don't see anything, then referring to the monitor PCB diagram which AJ attached earlier on, and the waveform diagrams which he attached in a later post, please first of all measure the supply voltage on test point TP1 (Should be 18V) and then scope the waveforms at the points indicated on the circuit diagram by numbers 1, 3, 13,14,15,16,17,and 18 in square boxes. The waveform diagrams posted by AJ show the scope settings you should use when scoping each point and the 'picture' you should expect to see on that point.

If you have any difficulty identifying the places to take measurements from let us know and we will try to guide you further.

[SiriusHardware]

One further question, is this a 9 inch or 12 inch monitor? We'd better make sure we are working from the right monitor diagram and if possible find the corresponding PCB layout diagram and track overlay.

A photo or two of the monitor PCB would be useful as well, Pudwink.

[ajgriff]

I hope it is a 12" monitor as all the diagrams I've posted relate to that version of the 4032. I'm fairly sure the 9" monitor was only used on the very early 4032s without the CRTC. This one has a CRTC. Confirmation needed though.

Alan

[pudwink]

Hi all
Yes it is a 12 inch monitor and here are the pictures of the board I am afraid I am useless at reading schematics and if someone can point out where on the crt board to take the readings from I can do it but first read my next post.

[pudwink]

pics of crt board

[pudwink]

I have taken readings following the youtube video I posted at the begining of this post off the mainboard video output might be of use
pic 1 horz drive
pic 2 vert drive
pic 3 video signal

[Sideband]

It would be better if you took photos off the scope with no flash. Can't see the waveforms properly although the line drive looks OK. Normally the vertical drive is a sawtooth (should be shown on the circuit).

If there is no vertical drive (but check where you are measuring it) the CRT may be blanked to avoid a screen burn, hence why nothing on the screen.

[Sideband]

Originally Posted by pudwink

Hi all
I am afraid I am useless at reading schematics and if someone can point out where on the crt board to take the readings from I can do it

So if you have the circuit, why not post it on here so we can show you where to check the necessary drive waveforms (although a good circuit drawing should give the main waveforms as well).

[ajgriff]

Originally Posted by Sideband

So if you have the circuit, why not post it on here so we can show you where to check the necessary drive waveforms (although a good circuit drawing should give the main waveforms as well).

See posts 23 and 40. Haven't yet found a board layout diagram.

Alan

[ajgriff]

Found it .......

Alan

[pudwink]

Hi
There was no flash on its just the way my phone took the pictures I took the readings as per the video off J7 on the main board as shown on page 18 of the 4000 series technical reference guide posted on here.

[ajgriff]

Originally Posted by pudwink

..... J7 on the main board as shown on page 18 of the 4000 series technical reference guide posted on here.

Actually that isn't the right schematic. It doesn't matter in this case as J7 and its connections are the same. The documents I've been posting relate specifically to your machine as far as I can tell. Also because they're extracted from the long document (which deals with three variants of the 4032) and the pages have been rotated you should find them easier to read/follow. See posts 15, 16, 23, 40 & 52. You may want to download the files and place them in a dedicated folder so you can easily refer to the relevant document whenever needed.

Alan

[Sideband]

It still looks like you have no vertical drive. Clearly shown as a squarewave but your scope is flatlining....

[ajgriff]

Originally Posted by Sideband

It still looks like you have no vertical drive. Clearly shown as a squarewave but your scope is flatlining....

Shouldn't the timebase be set to 5mS rather than 10µS for the vertical drive trace or am I missing something? Also the video signal should be a square wave although the timebase setting should be 10µS not 5µS.

Alan

[SiriusHardware]

I don't think the video waveform should be a squarewave, if you think about what is actually being displayed at the startup prompt it is a few characters on an otherwise dark screen, so what you will see on the video output will be a few thin positive spikes on a largely zero-volt level.

[SiriusHardware]

It still looks like you have no vertical drive.

Not sure that's true, if you go back to pud's earlier post with 5 images the one for the vert drive clearly shows two levels with a bit of bright line at the bottom of the screen. I think one part of the problem is that both beams are on so the upper one is getting in the way a bit, making the upper part of the lower trace look continuous.

Pudwink, see if you can turn the second channel on your scope off so there is only one trace on the screen and then scope the horizontal drive and vertical drive signals for us again. When you do the horizontal drive signal again, adjust the time/div control so that there are several high / low pulses on the screen. You will need to have the time/div control turned to quite a low setting in order to get that. Sorry to have to ask you to do this but it is important to definitely establish whether the vert-drive and horiz-drive signals are healthy before we go on to tackle what seems at the moment to be a monitor fault.

Would it be possible (anyone?) to mark up the track layout diagram with the places Pud needs to scope as asked earlier? The EHT for the tube is generated by the horizontal output so it's the 'horizontal drive' (what we would call horizontal sync) which initially needs to be followed through from the 'horizontal drive' input to the PCB to the main driver transistor for the LOPT.

I've just arrived back in so I won't be able to look at the layout diagrams etc until some time tomorrow.

[SiriusHardware]

AJ, where did you find the layout diagram? Is there a PCB track overlay diagram as well? We can mark up most of the required measurement points on the component layout you posted in #52 but it would be physically easier to get at some of them on the track side of the PCB.

[SiriusHardware]

"When you do the horizontal drive signal again, adjust the time/div control so that there are several high / low pulses on the screen".

As I keep saying, I shouldn't try to do this sort of thing late at night. I should have said "when you do the vertical drive again, adjust the time / div control so there are several high / low pulses on the screen.."