Commodore PET 3016

[John Earland]

No problem- do you mean a repeat of previous task?

[QUOTE=SiriusHardware;1243480]Sorry to ask, can you get those measurements again, but this time taking the connector pin closest to you as pin 1 and the one furthest away as pin 8, so counting from the one nearest to you...

1 0.09 (on 2V DC)
2 0.05 (on 2V DC)

(I am assuming there is a gap or something else between pins 2 and 3) Yes

3 0.02 (2V DC)
4 3.98 (20 V DC)
5 0.27 (2V DC)
6 0.117 (2V DC)
7 0.27 (2V DC)
8 4.32 (20V DC)

Also with your meter on AC volts, 200V AC range, could you measure the voltage between pin 1 and pin 2 (ie, red probe on pin 1, black probe on pin 2). 17 V

[SiriusHardware]

Your 17VAC is exactly the sort of figure I hoped to see on pins 1 and 2 as they are the AC power input to the monitor

I'm not really keen on the results for the other pins. They only make sense if the pin numbering for the 6-pin group on the other side of the gap runs the other way, with pin 3 furthest away and pin 8 next to the gap. (See attached sketch).

To settle this question I need you to power the machine off, and with your meter on 200 ohms resistance and (referring to the attached sketch for pin numbers) measure between the connector pin 4 and 0V, connector pin 6 and 0V, and connector pin 8 and 0V to see if those three connector pins are all connected to 0V. (Should be no or very low ohms resistance in each case).

If that's right, then move to pin 7 (as per attached sketch) and trace or measure the connection from that connector to wherever it goes on the PCB - probably to a nearby 1K resistor (R33) but possibly to a capacitor (C16).

[John Earland]

Originally Posted by SiriusHardware

Your 17VAC is exactly the sort of figure I hoped to see on pins 1 and 2 as they are the AC power input to the monitor

I'm not really keen on the results for the other pins. They only make sense if the pin numbering for the 6-pin group on the other side of the gap runs the other way, with pin 3 furthest away and pin 8 next to the gap. (See attached sketch).

To settle this question I need you to power the machine off, and with your meter on 200 ohms resistance and (referring to the attached sketch for pin numbers) measure between the connector pin 4 and 0V, connector pin 6 and 0V, and connector pin 8 and 0V to see if those three connector pins are all connected to 0V. (Should be no or very low ohms resistance in each case).
4 = 0
6 = 0
8 = 0

If that's right, then move to pin 7 (as per attached sketch) and trace or measure the connection from that connector to wherever it goes on the PCB - probably to a nearby 1K resistor (R33) but possibly to a capacitor (C16).

The only one that gives me a 0 reading is the capacitor labelled CR8 on the diagram-the small horizontal one in the photo which appears to be right next to pin 7!

[SiriusHardware]

The pins I decided to call pins 4, 6, and 8 are all connected to 0V? That's a great start.

But the pin I have suggested is pin 7 is connected to (diode) CR8? In that case, that pin is actually pin 3, or at least corresponds to pin 3 on the circuit diagram.

Let's redraw the connector again, this time oriented the way it looks to you looking into the rear of the monitor. (Attached).

You've now identified four of the group of six pins - three are zero volts and correspond to pins 4, 6, and 8 on the circuit diagram. The other one you have identified so far goes to CR8, and that tells us it is the vertical sync / vertical drive input (pin 3 on the circuit diagram).

The remaining two must be [video - in] and [horizontal drive / horizontal sync in].

Of the two pins marked '??', can you find out

-Which one is connected to one end of CR1 - that will be the Video input, corresponding to pin 5 on the circuit diagram.

-Which one is connected to one end of R33 (1K) or one end of C16. That will be the horizontal drive / horizontal sync input, corresponding to pin 7 on the circuit diagram.

[SiriusHardware]

Just caught your edit with the new photo.

I'm going to guess that the top unidentified pin goes to CR1, therefore is Video In.

The other one (third down from top) goes to that disc capacitor which is probably C16, and if so that will be the horizontal drive / horizontal sync in. Can you verify that?

[SiriusHardware]

By the way, if anyone is wondering why we heven't just looked at the layout diagram with its PCB foil patterns to work out where things are going, look again:

http://www.zimmers.net/anonftp/pub/c...deo-layout.gif

In particular, look at the foil pattern underneath the line output transformer, top left - the track / pad layout in that area bears no resemblance to the footprint of the line output transformer. Now look at the foil pattern in the top right area of the layout diagram. There are the pads for the line output transformer.

The component layout is correct but the foil pattern is left-right mirrored, shown as though looking at the underside of the PCB rather than looking through it, rendering it useless.

[John Earland]

Originally Posted by SiriusHardware

The pins I decided to call pins 4, 6, and 8 are all connected to 0V? That's a great start.

But the pin I have suggested is pin 7 is connected to (diode) CR8? In that case, that pin is actually pin 3, or at least corresponds to pin 3 on the circuit diagram.

Let's redraw the connector again, this time oriented the way it looks to you looking into the rear of the monitor. (Attached).

You've now identified four of the group of six pins - three are zero volts and correspond to pins 4, 6, and 8 on the circuit diagram. The other one you have identified so far goes to CR8, and that tells us it is the vertical sync / vertical drive input (pin 3 on the circuit diagram).

The remaining two must be [video - in] and [horizontal drive / horizontal sync in].

Of the two pins marked '??', can you find out

-Which one is connected to one end of CR1 - that will be the Video input, corresponding to pin 5 on the circuit diagram. - PIN 7 (PIN 5 on Circuit Diagram) - gave a reading of 06.6 Ohms

-Which one is connected to one end of R33 (1K) or one end of C16. That will be the horizontal drive / horizontal sync input, corresponding to pin 7 on the circuit diagram.

I'm getting confused and will start again!

[John Earland]

Originally Posted by SiriusHardware

Just caught your edit with the new photo.

I'm going to guess that the top unidentified pin goes to CR1, therefore is Video In.

The other one (third down from top) goes to that disc capacitor which is probably C16, and if so that will be the horizontal drive / horizontal sync in. Can you verify that?

Yes - there is a connection between the top pin and CR1
Yes - third one down goes to C16

[SiriusHardware]

This might be jumping the gun a bit, but, pulling everything we now know together, this is how I think the monitor input connector looks. Notice we're back to the pins being numbered 1-9.

On the second of three possible circuit diagrams, the input pins are numbered from 1-8, but on that diagram the horizontal sync input goes to a resistor (R33).

Since seeing John's new photo of the connector it is pretty clear that the horizontal sync input goes to a capacitor (C16) which rules out the second diagram. We're therefore back to diagram #1 or diagram #3, both of which have their input pins numbered from 1-9.

Now that it is obvious which pins serve which purpose it is also obvious that they should be numbered from 1-9 as shown in the (once again revised) sketch.

Transposing John's earlier voltage readings onto this layout, we get:

1 AC Power

2 AC Power

3 (Missing)

4 0.02 (0V)

5 3.98 (Vertical Sync Input)

6 0.27 (0V)

7 0.117 (Horizontal sync input)

8 0.27 (0V)

9 4.32 (Video in)

Circuit diagrams 1 and 3 both show the vertical sync to be normally high, active low and the horizontal sync signal to be normally low, active high but even so that average voltage of 0.117 on the horizontal input looks quite low.

Edit: Thanks for confirming the connections as outlined here. I'm still not sure, given the very low average voltage on the horizontal sync input, whether there actually is any horizontal sync. If only we had a scope or frequency meter.

[John Earland]

I could look at buying this? https://www.ebay.co.uk/itm/113877132370

[SiriusHardware]

I've only looked briefly but while it does look like a useful thing and it does have a basic frequency meter capability as well, the 'scope' part of it is very limited - doesn't go up to very high frequencies.

There was a recent thread elsewhere about LCD oscilloscopes, have a read through that if you can find it. I think you might be able to get a compact handheld LCD scope with better 'scope' capabilities for not much more than that meter.

I'm open to suggestions for any reliable 'bush mechanic' method of determining the definite presence of a sync waveform when the only instrument available is a multimeter.

[John Earland]

Originally Posted by SiriusHardware

I've only looked briefly but while it does look like a useful thing and it does have a basic frequency meter capability as well, the 'scope' part of it is very limited - doesn't go up to very high frequencies.

There was a recent thread elsewhere about LCD oscilloscopes, have a read through that if you can find it. I think you might be able to get a compact handheld LCD scope with better 'scope' capabilities for not much more than that meter.

I'm open to suggestions for any reliable 'bush mechanic' method of determining the definite presence of a sync waveform when the only instrument available is a multimeter.

What sort of frequencies should I be looking for?

[SiriusHardware]

You mean in a scope? At least 20MHz for hobby use, but the higher the better really. The frequency of the horizontal sync on your PET is only going to be between about 15KHz - 20KHz but if you are going to buy a scope for general electronics servicing, the higher the frequency it can go to the better.

Only thing is, more MHz = More Money.

[John Earland]

Originally Posted by SiriusHardware

You mean in a scope? At least 20MHz for hobby use, but the higher the better really. The frequency of the horizontal sync on your PET is only going to be between about 15KHz - 20KHz but if you are going to buy a scope for general electronics servicing, the higher the frequency it can go to the better.

Only thing is, more MHz = More Money.

I came across this: https://www.ebay.co.uk/itm/80MHz-Dig...Condition=3000

[SiriusHardware]

If you already had a frequency meter or you had a multimeter with a frequency measuring range on it, I would have asked you to use that to verify the presence or absence of your sync pulse waveform.

However, if you currently have neither a scope or a frequency meter then I would urge you to go for a scope rather than a frequency meter, because a scope is a much more versatile instrument.

If you did find that you had horizontal sync going to pin 7, the very next thing you would need to do would be to follow that signal further into the horizontal output stage, and for that, you'd really need a scope anyway.

[John Earland]

Originally Posted by SiriusHardware

If you already had a frequency meter or you had a multimeter with a frequency measuring range on it, I would have asked you to use that to verify the presence or absence of your sync pulse waveform.

However, if you currently have neither a scope or a frequency meter then I would urge you to go for a scope rather than a frequency meter, because a scope is a much more versatile instrument.

If you did find that you had horizontal sync going to pin 7, the very next thing you would need to do would be to follow that signal further into the horizontal output stage, and for that, you'd really need a scope anyway.

Ah - I see. I'll see what I can find.

[SiriusHardware]

When looking at older CRT scopes, the 'MHz' figure quoted is the figure to focus on. Typically you will find 20MHz, 40MHz, sometimes up to 100MHz, but they get very expensive once you get past 40MHz. In fact I find myself astonished at how much basic CRT scopes now seem to be going for. Not long ago, you could have picked one up for £10-£40 without having to fight somebody for it.

If looking at compact LCD scopes it is the 'Analogue Bandwidth' figure you need to take heed of.

I personally prefer analogue CRT scopes but they are big, heavy, fragile and usually quite old and temperamental with a glass CRT and a dozen fragile knobs and switches sticking out on the front, probably the last thing you want to see thrown out of the back of a delivery van.

You'd probably be better off getting one of the compact and much more robust digital LCD scopes, but I am not the person to ask about them. If you find one you like the look of, I suggest you wake up this other recent thread and ask for opinions about the particular one you want to know about.

https://vintage-radio.net/forum/showthread.php?t=165603

A word of caution though - links to current ebay items are frowned upon in this forum so to avoid running foul of the forum rules, state the detailed make / model number of any unit you want to know about, rather than providing a direct ebay link.

[John Earland]

Originally Posted by SiriusHardware

When looking at older CRT scopes, the 'MHz' figure quoted is the figure to focus on. Typically you will find 20MHz, 40MHz, sometimes up to 100MHz, but they get very expensive once you get past 40MHz. In fact I find myself astonished at how much basic CRT scopes now seem to be going for. Not long ago, you could have picked one up for £10-£40 without having to fight somebody for it.

If looking at compact LCD scopes it is the 'Analogue Bandwidth' figure you need to take heed of.

I personally prefer analogue CRT scopes but they are big, heavy, fragile and usually quite old and temperamental with a glass CRT and a dozen fragile knobs and switches sticking out on the front, probably the last thing you want to see thrown out of the back of a delivery van.

You'd probably be better off getting one of the compact and much more robust digital LCD scopes, but I am not the person to ask about them. If you find one you like the look of, I suggest you wake up this other recent thread and ask for opinions about the particular one you want to know about.

https://vintage-radio.net/forum/showthread.php?t=165603

A word of caution though - links to current ebay items are frowned upon in this forum so to avoid running foul of the forum rules, state the detailed make / model number of any unit you want to know about, rather than providing a direct ebay link.

That’s great advice-thank you. Yes-I was a bit nervous mentioning the dreaded EBay!

[John Earland]

Hi, having looked through the thread regarding LCD oscilloscopes - I found one that measures upto 30MHz Analog Bandwidth with 200MS/s Sampling rate. I think I will go for that.

[SiriusHardware]

Generally speaking any scope capable of working at 30MHz should be good enough for looking at video and sync signals.

Since you quote a sampling rate, I assume you went with an LCD scope. What make / model did you decide to go with, and are you getting a probe with it?

Edit: Sorry, I see you didn't actually choose yet. Definitely avoid the version which is only 5MHz tops, and if you go for the 30MHz version you will need to source a X1 / X10 probe separately, which will add to the cost.