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8032-SK Restoration

Gary C

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New toy picked up

Ebay picture.jpg

Reported as emitting a loud pop when they turned it on so some work to do. Shame the case didn't follow the hinge from the front design of previous machines, but once open, boy is it filthy inside.

Dirty motherboard.jpg

Initially looked like the transformer had failed

Mains transformer.jpg

But, it was the Mains RFI suppressor, which is probably not too bad, at least I dont have to think about rewinding the transformer.

RFI filter.jpg

I will probably just have to jumper this out as I cant find any spare units that look the same, not even sure who made it. Anyone know if there is a suitable visually similar unit made these days ? (and for the eagle eyed, yes it does only have three wires, the fourth was burnt so badly it fell out.)

Also the 8050 disk drive, when powered up does the red centre LED + green drive LED then green centre LED which suggests the drive unit PCB is healthy, which as a free addition is a plus.
 

Gary C

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Looking at the filter, it seems to be generally though to be unnecessary so I might just gut the cylinder, connect the wires together inside the cylinder, then pot with a suitable compound then refit. It would look the part but be bypassed.
 

daver2

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I think you want a tetanus jab before touching that :)...

That is the worst thing I have seen for a while (close to things in the dead pigeon loft)...

Dave
 

Gary C

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Its a bit manky :)

At least being basically an 8032, it should be saveable and it seems to be largely corrosion free which suggests its not been in a damp place.
 

Gary C

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Mains filter bypasses and transformer windings checked and all seems fine.

AC voltages as expected.

DIY lid prop fitted

Prop.jpg

Board powered up but no response. 5V rail measured at ~1.8V then UE4 decided to call it a day. Interestingly, this was the IC directly below the exploding mains filter so might have been shorted underneath by carbon. Time to whip it out and give it all a more thorough clean
 

Gary C

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Hum

UE4 is the oscillator chip and is a 74S04 and needs a S version to be fast enough and I only have a 7404 in stock and it don't work (I am now desperate ;) )

Time to hit the shops again.
 

Gary C

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:)

Found I did have the right chip but the wrong drawings. Replaced the chip but no activity at all on the CPU. Swapped that and now I get the four beeps. No image on the screen though, so that's a job for a different day.
 

Gary C

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Powered up and nothing from the video connector and nothing from the CRT controller. It was also obvious that the system crashed soon after the beeps to no sync on pin 7 of the 6502.

PETTEST installed and now the machine continues to run but nothing from the CRTC.

Dave, your PETTEST as downloaded should initialise the CRTC in an 8032SK without amendment ? its only the 40 column CRTC machines that need a tweak I believe.
 

daver2

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Gary,

>>> Dave, your PETTEST as downloaded should initialise the CRTC in an 8032SK without amendment ? its only the 40 column CRTC machines that need a tweak I believe.

You are correct.

Do you see an initial set of accesses to the CRTC on the chip select pin? This would be the firmware trying to initialise the CRTC.

I do believe my PETTESTER firmware has been tried previously in this type of machine with success.

Dave
 

Gary C

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As its just the later model of the universal dynamic board, then basically it seems to be just an 8032 in a fancy frock.

But the 6450 chip select line, just trying to look at that now

I take it, the PETTEST will initialise the CRTC so there should be a brief flurry of activity then its left to get on with running the timing and RAM access by itself ? I think I have a problem with X8XX but I see brief activity then nothing on the CPU's A11 so just wanted to check that would be as expected ?
 

Gary C

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Something odd. The CRTC isnt running the memory from the TA lines, but briefly I did get it to and BA11 started too.

More investigation (already checked the buffer)

Pin 20 on the CPU only ocassionally gives activity
 
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daver2

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>>> I take it, the PETTEST will initialise the CRTC so there should be a brief flurry of activity then its left to get on with running the timing and RAM access by itself ?

Correct.

Pin 25 (/CS) of the CRTC should have 16 (or so) pulses occurring just after a RESET.

Just organising a trip up to the sunny north for Thursday...

Dave
 

daver2

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You might also want to try a NOP generator and check BA0, BA2 and BR/W - any of these that are 'stuck' would mess the CRTC initialisation up.

Dave
 

Gary C

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It really was sunny today. :)

Shame, I am off to Scotland on Thursday to move one of the Kids into his new flat. First one to get a mortgage :)
 

Gary C

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So to make a NOP

Obviously I disconnect the data lines and spoof EA by connecting some to 0v and some to +5. Via 1k pull up ?
 

Gary C

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Yes, I saw that one and noted it didn't have any pull up resistors in the circuit unlike Daver2's suggested circuit.
 
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