Commodore PET working intermittently

[SiriusHardware]

John, a favour to ask - as you've probably seen there is another epic PET repair thread on the go - we are up to the point where you were a long time ago, needing to replace at least two of the IEEE 488 buffers.

I remember that the ones you bought were sold as MC3446 substitutes, but I can't remember what the devices were that you actually received and fitted. When you get a moment would you mind reading the part numbers off those?

[John Earland]

Originally Posted by SiriusHardware

John, a favour to ask - as you've probably seen there is another epic PET repair thread on the go - we are up to the point where you were a long time ago, needing to replace at least two of the IEEE 488 buffers.

I remember that the ones you bought were sold as MC3446 substitutes, but I can't remember what the devices were that you actually received and fitted. When you get a moment would you mind reading the part numbers off those?

Hi, yes of course. Let me trawl through my emails and I will get back to you asap. I obtained them from a chap in the Czech Republic I think! I'll have a look and get back to you.

[John Earland]

The actual numbers were 1820-1689 K8139
Hope that helps, J

[SiriusHardware]

Do they look like this?

[ortek_service]

I had tried looking again on https://dsmcz.com/prestashop/
that had been mentioned on the previous thread, I discovered via Googling MC3446 equivalent: https://www.vintage-radio.net/forum/...163589&page=13

However, it seems they no longer have any MC3446's (or the HP in-house part numbered 1820-1689 I've now tried).
So the MC3446AP - £4+VAT at Cricklewood Electronics - now seem the cheapest / easiest for these (Unless there are now others with stocks of the 1820-1689 numbered one)

[John Earland]

Originally Posted by SiriusHardware

Do they look like this?

Hi, yes these are the ICs.

[John Earland]

Originally Posted by ortek_service

I had tried looking again on https://dsmcz.com/prestashop/
that had been mentioned on the previous thread, I discovered via Googling MC3446 equivalent: https://www.vintage-radio.net/forum/...163589&page=13

However, it seems they no longer have any MC3446's (or the HP in-house part numbered 1820-1689 I've now tried).
So the MC3446AP - £4+VAT at Cricklewood Electronics - now seem the cheapest / easiest for these (Unless there are now others with stocks of the 1820-1689 numbered one)

Yes, fortunately I bought three at the time-which I have susequently needed! I believe they were the only ones they had but I am going back some time and assumed they would have more in. I'm assuming that the Cricklewood Electronics ones will work?

[John Earland]

My intermittent issue seems to be a problem with the reset line!

[John Earland]

There's this one for £14.39 https://www.littlediode.com/components/MC3446.html

[SiriusHardware]

Originally Posted by John Earland

My intermittent issue seems to be a problem with the reset line!

Can I ask what's led you to that conclusion?

[John Earland]

Originally Posted by SiriusHardware

Can I ask what's led you to that conclusion?

It's the voltage levels I've been told. Someone is kindly looking at it for me - not sure it's coming out of full reset. The reset to the CPU is going low but not fully high. I think that could also be a bad connector issue too.

[SiriusHardware]

As it's already in hand and you don't have it at the moment anyway, we won't interfere with the process but we are always interested to know about causes and effects, so it would be interesting to know what your looker finds.

[John Earland]

Originally Posted by SiriusHardware

As it's already in hand and you don't have it at the moment anyway, we won't interfere with the process but we are always interested to know about causes and effects, so it would be interesting to know what your looker finds.

I will certainly update the thread when I know more. I also think one of the 3446s has gone bad. Luckily I had bought three way back when, only used 2 so had a spare!

[SiriusHardware]

It it one of the recent replacements which you think has failed or is it the remaining, as yet unreplaced one? Interfaces like that are particularly prone to damage by connection / disconnection of an attached device while the power is on, so definitely don't get into the habit of doing that.

[John Earland]

Originally Posted by SiriusHardware

It it one of the recent replacements which you think has failed or is it the remaining, as yet unreplaced one? Interfaces like that are particularly prone to damage by connection / disconnection of an attached device while the power is on, so definitely don't get into the habit of doing that.

It's the original one. It was rather rusty too. The other two had gone previously so it was just a matter of time me thinks. It's got a new socket now which will help and I've just ordered a few more replacements for the 3446s just in case!

I will definately not do the connection/disconnection whilst power is on again!