Just got myself a commodore pet setup but not working

[ajgriff]

Originally Posted by 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.

Bo Zimmerman's site for the layout diagram:

http://www.zimmers.net/anonftp/pub/c...032/321449.gif

I don't think I've ever seen a track overlay diagram for a PET board. Personally I wouldn’t attempt any of this without using probe test clips so that my hands could be well away from the monitor when it’s live. Also I'd try to avoid releasing the PCB and take all the readings from the top of the board.

I'll reply to some of the points raised in your other posts in due course.

Alan

[pudwink]

Hi
I have took a video of the vert drive https://youtu.be/_8EFQLvQW70
only one channel is switched on also
pic 1 Horz drive
pic 2 video signal
Dont know if these are any better .

[ajgriff]

The timebase settings need to be as shown in the relevant waveform diagrams. Referring to diagrams 1, 3 & 13 in the '4032 Scope VDU' document they correspond to the video, vertical drive and horizontal drive signals. You will see that the correct timebase settings should be 10µS, 5mS & 10µS respectively.

Alan

[SiriusHardware]

Ref: The most recent waveform captures, horiz drive and video in the images in #62 look good - we can see that the video output is mostly low with very thin vertical spikes as expected, and Pud's video shows vert drive to be OK too, it's just that the scope is not triggering and holding the trace steady - but we can still see there is a valid waveform there so all good, which still leads us in the direction that the computer is OK but the monitor is not.

Pud could try Colin's suggestion earlier, enter that short line of BASIC (Followed by enter) and see if the computer generates a sound, as it should. That would further reinforce the idea that the computer is actually working.

You may also be able to do the same thing by pressing/releasing CTRL and G together although the machine might have to have CAPS-LOCK on for that to work. However, that's only an educated guess on my part, so if pressing CTRL-G makes the machine beep or bing, great, but don't worry if it does not.

[ajgriff]

Originally Posted by SiriusHardware

I don't think the video waveform should be a square wave, 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.

The thought had crossed my mind but I was going by the Technical Ref document. It’s possible that the square wave applies under certain test conditions not described in the document although it may just be that I haven’t spotted the relevant reference.

Originally Posted by SiriusHardware

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’m not convinced the vertical drive signal is missing either. The timebase needs to be set to 5mS.

Originally Posted by SiriusHardware

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.

Looking at the first image of post #48 I don’t think there’s a problem with the horizontal drive.

Originally Posted by SiriusHardware

Would it be possible (anyone?) to mark up the track layout diagram with the places Pud needs to scope as asked earlier?

These are the waveform test points for the vertical drive signal:

4-Base of Q611

5-Collector of Q611

6-Base of Q601

7-Base of Q621

8-Base of Q651

9-Base of Q652

10-Other end of R656 from the emitter of Q651

11-Junction of R622, C652 (+ve end) and R658

12-Junction of R663, R657 and C652 (-ve end)

These are the waveform test points for the horizontal drive up to and including the LOPT driver transistor:

14-Base of Q701

15-Base of Q711

16-Collector of Q711

17-Base of Q721

18-Collector of Q721

These are all easy to find on the layout diagram and the correct timebase plus vertical sensitivity settings are given on the waveform diagrams. Beware of the high voltages in the vicinity of these test points! Number 18 itself should peak at around 400V. The others are low voltage. Please note what I said in post #61 about using test clips and not releasing the monitor’s PCB.

Alan

[SiriusHardware]

I'd try to avoid releasing the PCB and take all the readings from the top of the board.

I get where you're coming from but, as you may have noticed, there is a large square opening in the 'roof' of the main enclosure which allows access to quite a lot of the track side of the monitor PCB - if we had a track overlay diagram that (the underside) would probably be the safest place to take measurements from.

[ajgriff]

I'd forgotten about the opening underneath but I'm not sure whether or not it's large enough on the 12" monitor. I honestly don't think there's much chance of finding a PCB overlay I'm afraid.

Alan

[ajgriff]

Pudwink

Please post scope trace photos for video, vertical drive and horizontal drive signals with the right settings (Time/Div and Volts/Div) so that we can be absolutely sure the signals are correct.

If we then need to look at the drive signals at the test points on the monitor’s PCB can you work from the descriptions I’ve provided in post #65? I don’t think marking up the top side view of the layout diagram would make things easier so I’m not inclined to spend time on it.

Alan

[ScottishColin]

There's some good photos here that show what looks like the same CRT PCB to me. Different motherboard though.

https://www.nightfallcrew.com/galler...t-4032-fat-40/

https://www.nightfallcrew.com/galler...0/IMG_0422.jpg

https://www.nightfallcrew.com/galler...0/IMG_0424.jpg

Colin.

[ajgriff]

That's a good find. In particular the track side image of the monitor's PCB could prove useful. I've flipped and tidied up the image a little. See attached.

Alan

[SiriusHardware]

Oh excellent, well done Colin and AJ, that is almost as good as a proper layout diagram, the only thing which spoils it a little is that flash reflection on the upper edge but we'll take it. Our thanks to whoever originally took the photo.

I am away from base at the moment - we'll give Pud a chance to answer AJ's question about whether the info already supplied is sufficient for him to be able to make the measurements we need. If it's not, no problem, we will mark up the relevant pickup points on the that PCB underside photo although it might take a day or two to do that.

[SiriusHardware]

Following on from AJ's observation about the rather high voltage expected on the collector of Q721 (waveform diagram #18) I think it would be best to abstain from that measurement for now and hope that one of the measurements of waveforms 13 through 17 will reveal some problem earlier in the chain.

If we have to scope the switching transistor collector we will need to know more about Pudwink's scope probes first.

[SiriusHardware]

I mentioned earlier on about doing visual checks on certain areas. The ones I have ringed on the attached image are especially important to check for circular cracks in the solder.

In the upper centre, T711 is attached to the PCB only by solder and is heavy, so if the unit has been transported around at any point during its life this is liable to put stress on its soldered connections. I notice that one of the pins (lower right) has been resoldered at some point on the example in the image.

At lower left, the Line Output Transformer is an even heavier part, again only secured to the PCB by the solder on its pins and these are a particular favourite for developing ring shaped cracks in the solder around their pins. You can probably see that ALL of the pins of the LOPT on the one in the image have been resoldered.

At mid / upper left there is the main horizontal output transistor mounted on a heatsink and this is prone to two separate problems, one is that due to the weight of the heatsink and transistor combined it will tend to wobble if the unit is transported and crack either the upper solder joints (ringed in pink) and the lower solder joint (ringed in yellow). The second is that when the unit is running the transistor will get hot and the heatsink will expand a little bit and when switched off it will cool down and contract a little bit. Solder is a soft metal so over the years this relentless expansion and contraction can also cause the solder around the studs of the heatsink to crack.

If the ones ringed in pink crack that will not cause a problem in and of itself but it will leave only the lower joint supporting the heatsink, and that is the important one because it carries the connection between the transistor collector and pin 3 of the LOPT.

Before attempting to read any waveforms from the PCB power off and look very carefully at these pins and make sure none of them have cracked solder connections. If there are cracks they can sometimes be near invisible, the way to reveal them is to rock the component slightly backwards and forwards while looking at the pins on the track side. Any pins with cracked solder joints will be seen to move independently of the PCB.

[SiriusHardware]

Assuming you don't find any visually obvious problems, here are the physical points from which to make the horizontal drive measurements on the track side of the PCB.

For the time being do NOT attempt to scope the waveform test point marked '18' but let us know what you get on scope test points 13 through 17. The scope waveforms you should see on those points were posted by AJ in post #40. When you look at them, notice that each diagram not only shows you what the trace should look like, it also tells you what the volts/div setting and time/div setting should be when making the measurement.

[ajgriff]

Attached is my attempt at highlighting the waveform test points on the track side of the PCB. Zoom in to see detail. The three signals we are looking at are colour coded as indicated by the legend in the bottom left hand corner. Each test point is numbered to correspond with the oscilloscope diagrams (1-18) extracted from the Technical Reference document (see post #40). I’ve done my best to minimise the effect of flash flare so that the areas we are interested in are clearly legible.

Notice that some of my test points don’t appear to be in the same place as the ones shown in the image posted by Sirius. In terms of connectivity there’s actually no difference between the two. For example, we’ve placed 18 on different solder pads but these are both connected to the case/collector of transistor Q721.

I’ve no idea whether or not pudwink is finding any of this helpful but at least the track side view will add to the bank of available PET resources. With that in mind I’m also attaching a cleaner version of the PCB (track side) without the test points relevant here but with various enhancements.

Alan

[SiriusHardware]

You should maybe consider offering your cleaned-up version of the track side view to the zimmerman site as that's the first place anyone goes for PET technical info and it seems to be a missing piece of information there, unless we just didn't find it.

[Courtney Louise]

If you fancy a trip down the road to Nuneaton I have 3 working Pet's here, two of them have identical boards to yours and you're welcome to bring yours and we can have a go at it. same with the FDD

[SiriusHardware]

At the moment we are fairly sure that the mainboard is generating the right video and sync signals so I think Pud would need to bring the whole machine so you could try a monitor transplant and / or attempt repair of the monitor if required.

[pudwink]

Hi
Thanks for the replys and courtney louise thank-you very much for your offer it will proberly be towards the back end of the week before I get a chance to look at the pet again due to work but if anyone thinks of anything else let me know and I will let everyone know the results as soon as possible.

[ScottishColin]

Pudwink - could you please power the PET on and type the line below and press Return and let us know if there's any sound. That way we'll know if the PET has booted or not, even without a screen.

? CHR$(7)

Colin.