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Old 20th Apr 2022, 8:21 pm   #81
ScottishColin
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Default Re: Perth PET

OK. I hesitate to say this but I'm back up and running. Here's what I did, but slightly frustratingly I cannot be 100% certain of what fixed the problems.

I removed all ROMs and inserted the Slothie test EPROM into UD9. That didn't work, so I powered off and then removed and reinserted the Slothie EPROM and the test started to work properly and reported no errors, either with RAM or the keyboard.

Having done that, I removed the Slothie EPROM and inserted the Daver2 EPROM into UD8. That didn't work. I then inserted the old ROMs into UD9 and UD7 and then the test started to work successfully again reporting no errors.

At the same time, I was having issues with the monitor flickering off - it seems like there is an intermittent problem with the two brown wires from the transformer. I have removed and reinserted the plug on the monitor board and the flickering has gone away.

I now can successfully boot the PET both from the original 6502 and the Tynemouth board. I have also tested the SD2PET which works successfully too.

So I guess it's either a problem with the ROM pins/sockets which I may have resolved by exercising the pins, or perhaps the PET needs the monitor to be working properly at boot (although I'm not clear if the PET is really that clever).

So. Working.

For now.

Thanks all.
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Old 20th Apr 2022, 10:50 pm   #82
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Default Re: Perth PET

That's good news Colin! I guess it was always going to be an intermittent connection of some sort.

Alan
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Old 20th Apr 2022, 10:57 pm   #83
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Default Re: Perth PET

For information, as stated somewhere a while further back, the Daver2 test EPROM requires that a working original UD9 is fitted, plus the character generator PROM UF10.

Slothie's requires only UF10 to be fitted, all other PROMs can be missing.

Were the PROM sockets ever replaced or are they still the original Commodore parts?
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Old 20th Apr 2022, 11:06 pm   #84
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Welcome back - I have at some point replaced the UD9 socket in this process.

Colin.
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Old 20th Apr 2022, 11:21 pm   #85
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I'm not quite back yet - still just using a phone for net access (which I don't enjoy) and have none of my usual resources available. It sounds as though the machine could start grumbling again but while it is working there is unfortunately no fault to trace. We'll just have to start fresh if any new symptoms appear.

I remember you did have to replace the UD9 socket because inserting the turned-pin 'adaptor' in which the original Slothie EPROM was fitted seemed to have spread / damaged the contacts in the original socket. I think when I did Retromit's Slothie EPROM I made it using a conventional socket with flat pins as the 'carrier' so that would not happen again.
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Old 21st Apr 2022, 7:54 am   #86
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Default Re: Perth PET

The one I'm using right now (Retromit's) has a conventional socket as you say.

I wonder if there is any kind of handshake between the motherboard and the monitor at power on to see if the monitor is 'ready' and whether that got in the way of booting this time.

As you say - I expect I'll have more problems here with this one, especially with the amount of inexpert soldering that I have done here on an old motherboard - I think I'm getting more confident at Problem Determination at least though.

Disk Drive next - when a cable arrives anyway.

Colin.



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Originally Posted by SiriusHardware View Post
I'm not quite back yet - still just using a phone for net access (which I don't enjoy) and have none of my usual resources available. It sounds as though the machine could start grumbling again but while it is working there is unfortunately no fault to trace. We'll just have to start fresh if any new symptoms appear.

I remember you did have to replace the UD9 socket because inserting the turned-pin 'adaptor' in which the original Slothie EPROM was fitted seemed to have spread / damaged the contacts in the original socket. I think when I did Retromit's Slothie EPROM I made it using a conventional socket with flat pins as the 'carrier' so that would not happen again.
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Old 21st Apr 2022, 7:58 am   #87
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Default Re: Perth PET

The 'conversation' between the computer and the monitor is entirely one-way, the computer (when working) generates sync pulses which 'activate' the monitor. If no sync pulses, the monitor does not run.

You could try the SD2PET - a good workout / test for the IEEE port in preparation for any efforts on the disc drive.
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Old 21st Apr 2022, 8:37 am   #88
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Default Re: Perth PET

Understood re handshake - there isn't one.

I briefly tried the SD2PET last night and it worked first time - I intend to play with it some more this weekend.

It led me to realise that even though they are the same size, there's a difference between the IEE port and the User Port though......

This looks interesting:

http://www.6502.org/users/sjgray/pro...ort/index.html

Colin.


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The 'conversation' between the computer and the monitor is entirely one-way, the computer (when working) generates sync pulses which 'activate' the monitor. If no sync pulses, the monitor does not run.

You could try the SD2PET - a good workout / test for the IEEE port in preparation for any efforts on the disc drive.
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Old 7th May 2022, 9:58 pm   #89
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Ok. As you suspected I'm back because the same symptoms are back after a couple of good weeks. With the Tynemouth ROM/RAM in I get the right boot screen, but with a few extra characters dotted around and the keyboard doesn't work.

If I use Slothie's ROM or Dave's they do nothing.

I'm wondering if it's either the 6502 socket - although new, it has had a lot of insertions of the CPU, or perhaps UF10.

Any good ideas where I should start?

Colin.
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Old 8th May 2022, 9:48 am   #90
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If you suspect a socket, one thing you can try is, with your scope and a needlepoint probe, go round all 40 pins of the IC putting the probe first on the top shoulder of the IC pin, then on the contact of the socket. Be careful not to join the pin and the socket contact together with the probe tip itself.

All things being normal, you should see the same scope 'picture' on the IC pin and the associated contact, whether it is a steady voltage or a waveform of some sort. Where you see a difference between the 'picture' on the IC pin and the 'picture' on the associated IC socket contact, that would mean that the two are not connected together, although of course they should be.

Of course you could arrive at the same end just by measuring the resistance / continuity between each IC pin and the associated contact but it can be quite difficult to get the comparatively 'fat' ends of two meter probes onto the required points without them making contact with each other.

A reminder, for the Daver2 EPROM to function in UD8 position the original UD9 must also be fitted.

Last edited by SiriusHardware; 8th May 2022 at 9:54 am.
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Old 8th May 2022, 4:33 pm   #91
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Default Re: Perth PET

Also if you suspect a turned pin socket, but visual inpection shows none of the gold inserts missing, as a last resort you can plug another new turned pin socket into the suspect socket and then fit the chip into that socket. This is a last resort because the pins on the new socket that are intended to solder into a pcb are slightly larger than IC pins and larger than the male header pins that plug into turned pin sockets. The original socket will probably never be reliable after this without keeping the piggyback socket fitted.

Last edited by Mark1960; 8th May 2022 at 4:34 pm. Reason: Typo
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Old 10th May 2022, 9:54 pm   #92
ScottishColin
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Default Re: Perth PET

Here's where I stand today. I have not taken the motherboard out and checked continuity from the underneath to the chip pins of those in turned pin sockets as suggested - I'll get on with that tomorrow.

I have removed the ROM/RAM kit so I just have the 6502 in C4. I have a Slothie EPROM and a DaveR2 EPROM but I can get neither of them to kick into life.

The screen I get is attached - it's pretty consistent but does vary from power cycle to power cycle.

I have dug out my scope and have my meter to hand to start checking, but I'm afraid I need your help to get me going again - I have reseated every chip that I can to no avail. I have tried reading though my old thread but I'm not sure where to jump in using that information.

Thanks in advance.

Colin.
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Old 10th May 2022, 10:08 pm   #93
SiriusHardware
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Default Re: Perth PET

To my casual eye that screen says that the video circuit is still working, but the code which should clear the video RAM is never being executed, or it does run but a hardware fault is preventing bytes from being written to the video RAM.

We'll let you get through with the connection checks first, because when you have a situation where the machine works / doesn't work / works again / doesn't work that is unlikely to be a chip failing / healing / failing, it is more likely to be a physical problem.

A chip which fails will usually stay failed once failed, although I should say - to cover my own rear exit - that it is not entirely unheard of for silicon to go intermittent. It's just more likely that this is a connection, like a bad socket receptable, broken track, broken solder joint or faulty through hole VIA coming and going.
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Old 10th May 2022, 11:52 pm   #94
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Default Re: Perth PET

Another couple of possibilities for intermittent problems are

Component lead bent over on the back of the board and touching something else, creating an intermittent short.

A piece of loose wire, component lead etc floating about under one of the sockets.
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Old 11th May 2022, 1:01 pm   #95
ScottishColin
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Default Re: Perth PET

Two things:

1) I got my can of air out and sprayed under every new socket and it worked for one boot. Job done I though so I powered down and went back later to be met with the same screen as in post 92. That has stayed like that since through several reboots.

2) I'm doing simple continuity checks and wonder what a 'good' reading is. On my meter I get the sound/green light for continuity n some pins, but the resistance reading can be over 1 ohm. Is there an unacceptable resistance continuity reading that still gives me continuity?

My next task is to use the schematic and track every pin on all replaced chips to the pins' source/destination elsewhere to see what readings I get then.

Thanks

Colin.
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Old 11th May 2022, 1:17 pm   #96
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Default Re: Perth PET

Where the circuit diagram indicates that two points should be directly connected together, anything which shows more than about 1-2 ohms would be cause for further investigation.

Bear in mind that your meter leads may have a small amount of resistance which is included in the total resistance reading, so start by seeing what the meter indicates when you just touch the probes directly together. Anything more than that reading is accounted for by the resistance of the connection under test.

The problem with the continuity test mode on most meters is that it often beeps even when the resistance is relatively high, sometimes in the hundreds of ohms, so don't assume that a beep from the meter means that the two points you have the probes on are closely connected or shorted together. Always look at the meter reading as well.

Those air cans can have the secondary effect of cooling / frosting whatever you spray with them as the residue evaporates, so maybe it was the act of cooling a socket or joint (or possibly chip) which did the trick.

Here's a left-field idea (not compulsory). Put the whole PCB in the fridge, if it will fit, for an hour or two, then quickly fit it and see if it works until it warms up.
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Old 11th May 2022, 3:05 pm   #97
ScottishColin
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re the fridge - nope. It had an hour but made no difference.

Colin.
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Old 11th May 2022, 3:24 pm   #98
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OK, carry on with the metering out, if you have the patience to do that.
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Old 11th May 2022, 3:32 pm   #99
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Looking ahead, do you still have that NOP testing rig (or does your Ram / ROM Gizmo have a facility like that built in?)
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Old 11th May 2022, 5:02 pm   #100
ScottishColin
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I have it - I'd need to re-check it (pins/resistors) but I do still have it.

Colin.

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Looking ahead, do you still have that NOP testing rig (or does your Ram / ROM Gizmo have a facility like that built in?)
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