• Please review our updated Terms and Rules here

Neglected PET needing some love

Divarin said:
I don't (yet) have a meter that'll give me a frequency.
Click to expand...
To measure the DC average of a pulse waveform, only a normal VOM is necessary. Do you have one? If you get something like 2.5 V on the horizontal signal that it means it is pulsing like a square wave. If you get zero or 5 V, it means it is not pulsing and the CRT Controller (6545) has not been initialized to generate the proper signals. That may indicate the PET is not booting very far before it hangs. In that case do not worry about the RBG board until the CRTC is running.
 
...1 kHz (or so) squarewave signal. If that is not working on your oscilloscope...
Click to expand...

As far as we can see there is something coming out of the CAL output on the Hickok but the apparently non-working trigger does not allow for it to be displayed steadily enough to be used to set up the probes. For that purpose only, the red knob on the time / division control could be turned away from the CAL position and adjusted until the trace is hardly moving so that the shape of the waveform can be seen and adjusted with the probe on the x10 setting.

It is still possible that operating each of the trigger-related switches in and out a hundred or so times will 'fix' the trigger problem. It has to be worth a try, it would cost nothing but a little of Divarin's time. If it makes any kind of difference, even if only temporary, then cleaning the switches properly (with switch cleaner) might effect a more permanent cure.
 
The Hantek 6022 was actually the exact scope I was considering.

I see what you mean about the average of the waveform, on the horizontal I'm getting 3.68 volts with my multimeter.

As for this scope, yes I tried working the buttons quite a bit I guess I could open it up and spray some deoxit in the switches and knobs.
 
ScottishColin who lurks around here bought one of those and it was instrumental(!) in the process of tracing through the many problems his PET had. If you need to know anything about them I'm sure Colin will be happy to advise either here, in a specific thread or via PM / DM.
 
Divarin said:
I see what you mean about the average of the waveform, on the horizontal I'm getting 3.68 volts with my multimeter.
Click to expand...
OK I checked the schematic of an older 8032 which shows the input Horizontal waveform and it does have a high duty cycle waveform so 3.7 V may be correct. Of course the measurement does not indicate the frequency so we do not know if it is the correct 20 KHz, but it is promising.
The Vertical waveform has such a skinny negative pulse that with that high a duty cycle it would show about 4.9 V which may be difficult to tell from no signal, a flat 5 V.

http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/8032/321448.gif
 
dave_m said:
OK I checked the schematic of an older 8032 which shows the input Horizontal waveform and it does have a high duty cycle waveform so 3.7 V may be correct. Of course the measurement does not indicate the frequency so we do not know if it is the correct 20 KHz, but it is promising.
The Vertical waveform has such a skinny negative pulse that with that high a duty cycle it would show about 4.9 V which may be difficult to tell from no signal, a flat 5 V.

http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/8032/321448.gif
Click to expand...
When I measured the vertical (with the multimeter) it was near 0 (like 0.07) and slowly dropped to zero but given that this is an average that of course doesn't mean there's nothing there just that it averages out to (almost) zero. I can see a signal on the scope so I know it's not missing I just can't get a clear enough picture with this scope to tell if it's correct.

One nice thing about the Hantek, when I get it and figure out how to use it, is that I won't have to snap pictures with my phone I can just alt+print screen and paste. It's been especially annoying since the USB port on my phone stopped working about a year or so ago and the only way I can get pictures off is to either shut it down and pull the memory card out or let it back up to "the cloud" and download it.
 
Divarin said:
When I measured the vertical (with the multimeter) it was near 0 (like 0.07) and slowly dropped to zero but given that this is an average that of course doesn't mean there's nothing there just that it averages out to (almost) zero. I can see a signal on the scope so I know it's not missing I just can't get a clear enough picture with this scope to tell if it's correct.

One nice thing about the Hantek, when I get it and figure out how to use it, is that I won't have to snap pictures with my phone I can just alt+print screen and paste. It's been especially annoying since the USB port on my phone stopped working about a year or so ago and the only way I can get pictures off is to either shut it down and pull the memory card out or let it back up to "the cloud" and download it.
Click to expand...

There's a stop button too, so when you get the results you're after, you can pause the scope and then take the screenshot (or snip it).

Colin.
 
Divarin said:
When I measured the vertical (with the multimeter) it was near 0 (like 0.07) and slowly dropped to zero but given that this is an average that of course doesn't mean there's nothing there just that it averages out to (almost) zero. I can see a signal on the scope so I know it's not missing I just can't get a clear enough picture with this scope to tell if it's correct.

One nice thing about the Hantek, when I get it and figure out how to use it, is that I won't have to snap pictures with my phone I can just alt+print screen and paste. It's been especially annoying since the USB port on my phone stopped working about a year or so ago and the only way I can get pictures off is to either shut it down and pull the memory card out or let it back up to "the cloud" and download it.
Click to expand...

While you're waiting, here's a 35 minute review from Adrian's Basement of Youtube.


Colin.
 
Divarin said:
When I measured the vertical (with the multimeter) it was near 0 (like 0.07) and slowly dropped to zero but given that this is an average that of course doesn't mean there's nothing there just that it averages out to (almost) zero. I can see a signal on the scope so I know it's not missing I just can't get a clear enough picture with this scope to tell if it's correct.
Click to expand...
I have a late model 8032 board (8032090) and I get 1.6 V for the Vertical Drive and 2.0 V for the horizontal drive signal using both a VOM and DVM with DC selected. That's much different than your PET readings. This data is confusing to me so I will have to dig up my scope and check the waveforms.
 
As Divarin has committed to acquiring a new scope, probably the path of least resistance is to let it arrive, and then those of you who know these machines well will be able to ask tor whatever measurements you need.
 
dave_m said:
I have a late model 8032 board (8032090) and I get 1.6 V for the Vertical Drive and 2.0 V for the horizontal drive signal using both a VOM and DVM with DC selected. That's much different than your PET readings. This data is confusing to me so I will have to dig up my scope and check the waveforms.
Click to expand...
I wonder if this is because I'm running my pet without the monitor connected, maybe there's a different reading when the monitor circuit is drawing a load? Just guessing.
 
Divarin said:
I wonder if this is because I'm running my pet without the monitor connected, maybe there's a different reading when the monitor circuit is drawing a load? Just guessing.
Click to expand...
Nope - it is predominantly a TTL signal and not something that feeds a 50 or 75 Ohm terminator...

It is all to do with the pulse width and frequency. Some models of PETs also have the drive signals swapped over - so they either pulse high or pulse low.

Dave
 
daver2 said:
It is all to do with the pulse width and frequency. Some models of PETs also have the drive signals swapped over - so they either pulse high or pulse low.
Click to expand...
I agree, but if he has a 8032 which his board photo indicates, I'm guessing his 6545 CRTC is not being initialized by the PET ROM or is not working. His new scope will tell us if he has the correct timing signals.
While awaiting China, he should run your pettest which may perk up his CRTC.
 
dave_m said:
I agree, but if he has a 8032 which his board photo indicates, I'm guessing his 6545 CRTC is not being initialized by the PET ROM or is not working. His new scope will tell us if he has the correct timing signals.
While awaiting China, he should run your pettest which may perk up his CRTC.
Click to expand...

Where can I get this PETTEST? It is a program that runs on the pet?
 
It is on my google drive - or there is a copy on Zimmers at http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/other/PETTESTE2KV04.zip.

It is a program that you burn into a 2716 (or similar) EPROM and you put that in place of the EDIT ROM in your PET. The EDIT ROM is the only ROM that is pretty much guaranteed to be in a socket (as it defines the locale/language for the PET).

The extensive documentation is in the ZIP file. Can I suggest reading the manual before using it though...

The PET requires a minimum of hardware to execute - but the RAM and a significant number of the BASIC ROMs can be faulty - and all of that is tested by my diagnostic.

Some of the test reports can be a bit cryptic (especially if you are trying to identify the pattern to isolate a fault), but, as the author, I can help you with this activity...

Dave
 
daver2 said:
It is on my google drive - or there is a copy on Zimmers at http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/other/PETTESTE2KV04.zip.

It is a program that you burn into a 2716 (or similar) EPROM and you put that in place of the EDIT ROM in your PET. The EDIT ROM is the only ROM that is pretty much guaranteed to be in a socket (as it defines the locale/language for the PET).

The extensive documentation is in the ZIP file. Can I suggest reading the manual before using it though...

The PET requires a minimum of hardware to execute - but the RAM and a significant number of the BASIC ROMs can be faulty - and all of that is tested by my diagnostic.

Some of the test reports can be a bit cryptic (especially if you are trying to identify the pattern to isolate a fault), but, as the author, I can help you with this activity...

Dave
Click to expand...
Thanks I'll start reading the pdf.
 
Can the 2716 be used as a direct replacement for the 2316 that's in the pet right now? Or do I need to build an adapter?
 
You must log in or register to reply here.
Back
Top