Is there still hope for this Osbourne 1?

I have an Osbourne 1 that I am trying to restore. It's round two. I first looked at it in 2009. A capacitor in the power supply went pop, so I replaced the three similar ones on the power supply.
Once that was done the PC started to work seemingly well for a few days. But then it suddenly failed, and there was nothing on the screen. I put it aside at that point.

But I have opened it up to inspect it again, with a mind to get it going.

The power supply looks visibly fine. (I will get to measuring the voltages it produces soon).

But open inspecting the motherboard, I found that the Reset pin on the Z80 has melted, like an awful current has been through it. (pictures attached. The Z80 has, in this photo, been lifted by me from the socket).

Can it be said was the likely prognosis is for this. If the Reset pin on the Z80 has been zapped, how wide spread is the likely damage? Is is worth just trying to replace the Z80 chip? (subject to testing the power supply).

Kind regards,
Richard

If the reset pin had been melted by too much current, the line towards the pin would have melted looooong before the pin did. I think the pin broke off and the previous owner soldered a pin to it and using the socket as an holder.
You can start with replacing the Z80. The board itself looks fine so if that doesn't help, start replacing the parts that have been placed in a socket. After that ask people who have Osborne experience.

Good luck!

That is a very insightful point, Ruud. Thank you. There are no burned out traces around the Z80, or the reset switch.
What then explains the messy orange material around the socket?

Could it just be solder flux residue?

I have measured the power supply DC voltages. It is giving a steady 12.42V and 5.17V.

Do NEVER lose hope.
I completely agree with @Ruud. I would also reccommend you to replace the socket.

All hope is lost.. Abandon ship. I mean they dont even know what the word "reasonable" means in Reasonable offer....

They did it, they blew it up. Those damn dirty apes....

Yeah, that looks like someone did something stupid and bodged over it. Probably first broke the pin, then made a complete mess trying to solder a random bit of wire to the socket, which isn't even close to a sensible solution.

I'd replace the socket too, and I'd try to start by just pulling off its plastic part (some sockets can come apart that way) so that I can desolder the pins one-by-one, much easier than trying to get out a broken socket in one piece. Failing that, I'd try to nip it off in bits, anything so I could remove the pins one at a time, and avoid messing up the circuit board.

Bruce Tomlin said:

I'd replace the socket too

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This, absolutely.

Ya, there's even a blob of solder on the pin next to the reset "pin"



Definitely replace the socket and the CPU.

Thank you all. I think the broken CPU pin and bad fix up is the explanation that matches all the evidence.
I agree the best fix is to replace the socket and the Z80. I will heed the advice in progressing that. Thank you.

It also occurred to me, that for debugging purposes, I could remove this addon board, and plug a new Z80 chip directly into the socket on the main board, and see if the machine will run like that.

rcroy said:

I will heed the advice in progressing that. Thank you.

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Do you have any experience desoldering through-hole components? I'm guessing you don't have a desoldering gun, or you wouldn't have asked I've used one of these with great success. Some people have success with solder wick and flux, but I find I can remove through-hole stuff pretty quickly with that solder sucker. For something with that many pins, if you can carefully snip the plastic socket apart from the top so that you only have to desolder one or two pins at a time, it will make it easier.

Yes, I have seen de-soldering guns used on YouTube. While I don't, myself, have much experience or gear, I have friends and colleagues who have up to professional experience and gear. So together with them I have hope we can do it!

Temu offers a clone of the old big Edsyn Soldapullt for cheap. It's an exact copy of my 40-year old tool that I use--the parts are even interchangeable. Also, get a set of hollow stainless steel needles for clearing holes--again, cheap.
I trust you have a temperature-controlled soldering station? If not, Temu is your friend again.

But then again, I note that you spell Adam's surname as "Osbourne", so I'm guessing that you're in the UK. (Adam spelled it without the "u"... ) I don't know if Temu has a presence in the UK...

I note that you spell Adam's surname as "Osbourne", so I'm guessing that you're in the UK. (Adam spelled it without the "u"... ) I don't know if Temu has a presence in the UK...

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Oh, yes, it's spelt 'Osborne'! That does give away my anglo heritage. But I live in New Zealand. Trust me, TEMU is global, saturated global. I hear mixed reviews.

Temu, like any other import sales outfit, is quite variable. I can speak only to my experience, which has been good thus far.