Uh Oh.Electron inbound

Any 8bit repairs, images, cool things, upgrades etc.
User avatar
rubber_jonnie
Site Admin
Site Admin
Posts: 10462
Joined: Thu Aug 17, 2017 7:40 pm
Location: Essex
Contact:

Re: Uh Oh.Electron inbound

Post by rubber_jonnie »

stephen_usher wrote: Sun Jun 20, 2021 2:05 pm :dualthumbup:
Ok, resistance checks are done, and I did have to swap over the +ve and GND leads to get a reading. Power was off.

They are a long way off 25K though, which was what was suggested they should be over at *.

A0-A12 & A15 all read 400K

A13 read 40K.
A14 read 22 ohms.

Potential CPU fault then?
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
User avatar
stephen_usher
Posts: 5578
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: Uh Oh.Electron inbound

Post by stephen_usher »

Oh! 22 ohms of A14. That would be why it's low then!

Are there any other components between the CPU's A14 and the ULA?

To be honest, without the CPU being out of the circuit it's probably impossible to determine where the fault is.

Actually, IC17 (74LS00) and one ROM are on that same bus aren't they? Hmm... I'd still remove the CPU myself so as to try to find the fault. Once it was out I would check the resistances again.

Did you check the resistance between the address lines and VCC so as to see what the pull-ups are?
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
User avatar
rubber_jonnie
Site Admin
Site Admin
Posts: 10462
Joined: Thu Aug 17, 2017 7:40 pm
Location: Essex
Contact:

Re: Uh Oh.Electron inbound

Post by rubber_jonnie »

stephen_usher wrote: Sun Jun 20, 2021 5:30 pm Did you check the resistance between the address lines and VCC so as to see what the pull-ups are?
I did measure them, yes, and all come in at 56K other than A13 & A14.

A13 reads 40 ohms, A14 I can't get a clear read on it right now as I snipped it after talking to hoglet over on *.

IIRC it as not 56K though, it was much lower. I'm swinging more and more towards just pulling the CPU and dropping in a socket so I can test with a known good CPU.

If that doesn't work then we know it's most likely to be the ULA or the ROM.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
User avatar
rubber_jonnie
Site Admin
Site Admin
Posts: 10462
Joined: Thu Aug 17, 2017 7:40 pm
Location: Essex
Contact:

Re: Uh Oh.Electron inbound

Post by rubber_jonnie »

Ok, there will be an interlude now I think. We may need to move house a week sooner, which is next week, so I'm packing things up ready to go.

I'll keep you posted.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
User avatar
stephen_usher
Posts: 5578
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: Uh Oh.Electron inbound

Post by stephen_usher »

Good luck with the move!
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
User avatar
rubber_jonnie
Site Admin
Site Admin
Posts: 10462
Joined: Thu Aug 17, 2017 7:40 pm
Location: Essex
Contact:

Re: Uh Oh.Electron inbound

Post by rubber_jonnie »

stephen_usher wrote: Mon Jun 21, 2021 2:56 pm Good luck with the move!
Thanks, I'm sure it'll go just fine.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
User avatar
JezC
Posts: 2081
Joined: Mon Aug 28, 2017 11:44 pm

Re: Uh Oh.Electron inbound

Post by JezC »

Certainly hope it goes with minimal fuss... always lots of stress though!

I might have to find an excuse to put some carpet offcuts on the garage floor and cover up the breeze block walls.
Will follow your updates with interest as you get setup in the new house.
User avatar
rubber_jonnie
Site Admin
Site Admin
Posts: 10462
Joined: Thu Aug 17, 2017 7:40 pm
Location: Essex
Contact:

Re: Uh Oh.Electron inbound

Post by rubber_jonnie »

JezC wrote: Mon Jun 21, 2021 3:27 pm Certainly hope it goes with minimal fuss... always lots of stress though!

I might have to find an excuse to put some carpet offcuts on the garage floor and cover up the breeze block walls.
Will follow your updates with interest as you get setup in the new house.
Thanks, fingers crossed we'll be out of here ASAP as it's getting uncomfortable here now and we want to be gone.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
User avatar
rubber_jonnie
Site Admin
Site Admin
Posts: 10462
Joined: Thu Aug 17, 2017 7:40 pm
Location: Essex
Contact:

Re: Uh Oh.Electron inbound

Post by rubber_jonnie »

Right, since I've located my de-solder gun, I can get cracking on this little guy again :)

I had a delivery of CPUs the other day too and sockets, so I think I'll just go for replacing that and see what's what.

If it is still dead after that, then there isn't much else it can be other than the ULA. I'm hoping it isn't, as that is a tougher nut to crack.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
User avatar
rubber_jonnie
Site Admin
Site Admin
Posts: 10462
Joined: Thu Aug 17, 2017 7:40 pm
Location: Essex
Contact:

Re: Uh Oh.Electron inbound

Post by rubber_jonnie »

And the word is: ULA

Sadly after a CPU transplant it still has the exact same pattern of white bars on screen. I haven't got the 'scope out yet (I haven't found it yet, but it's here somewhere!) but pretty much all it can be now is the ULA.

I may try swapping out the last 3 RAM ICs since I am in a much better position for IC removal/replacement now I have my desolder gun again, but it really does look like the ULA, so on the hunt for a replacement.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
Post Reply

Return to “8 BIT CORNER”