Spectravideo 328 - Its dead Jim!

[kiwi_steve]

it is an ex-parrot... it has ceased to be!

I picked it up this afternoon and after talking with the guy (a Tait employee... so I figured at that point it might have been played with) it seemed like he thought maybe it would be a power supply fault...

... so I opened it up, checked the voltages from the power pack, and the voltages on the regs - which are fine... which means the fault lies deeper... and I discovered there was some post-jiggery-pokery damage as well... which bodes unwell.

[tezza]

Eww..don't you hate that. Broken stiff multiwire ribbon cables can be a bitch to fix. Not impossible though. Strip back the wire and solder.

Is that a lifted trace by R26?

[kiwi_steve]

No, but the broken wire is the ground for the keyboard... I'm just about to re-attach that. If I get it going I will rewire the keyboard with some ribbon I have here - not as robust, but much more flexible. If I get really keen I will dismember some old hard drive cables and connectors and make it pluggable

I've had it plugged into the monitor and I get a flash of 'black' and a beep... thats all, but thats something. Seems like its either booting or trying to boot. I'm off to do some keyboard jiggery pokery now... watch this space I'm hoping for a functional caps lock LED and power LED when I'm done... small steps.

Steve

[kiwi_steve]

Ok, I now have a power LED (not surprising really, its just an indicator that the +5V supply is functional) and a beep (not sure where thats coming from, but its getting right through the modulator board and out the audio connector). Still just a black screen, and the caps lock key is non-functional... might be more than I can trace with just a small multimeter, but I'll give it a go

[kiwi_steve]

Just for future reference, the power supply in these machines is pretty rough-and-ready. Here is the circuit diagram (I have a copy of all the circuit diagrams for this machine, courtesy of samdal.com).



And here is where the regulators sit:



The 7805 and 7812 are +VE voltage regulators - 5 and 12 V respectively. They can handle 1A each which should be enough... although they have very high relative voltages going into them... I'm almost surprised they didn't suffer from failures over time. The pinouts when looking at them from the front are 1.input, 2.ground, 3.output

The 79-series are -VE regulators - the 7912 is a -12V reg, but the pinout is different on 79xx's. Pin 1 is ground, 2.input, 3.output. Once again, 1A current capacity.
The 79L05 is a low current version (100mA) and hard to see in my crappy photo - but its in a small black transistor casing. The pinout is the same as its big brother, taken when looking at the flat face with the pins facing down. Its 1.ground, 2.input, 3.output. (The output pin is closest to the back edge of the pc for the 79L05).

Having said that, all 4 rails are at the right voltage in my one so its not that... but I thought I would document it in case anyone else has a faulty one.

Steve

[tezza]

Good luck. Keep us posted.

[gnewtonaus]

Great to see people still have these wonderful old machines. I've started to get back into them myself recently and I'm in the process of repairing a Spectravideo SV328 MkII myself at the moment. I bought it on eBay "as-is/for parts". I'm determined to get this little gem going again. I'm documenting it all on my website at https://sites.google.com/site/walztroni ... i-328-mkii if you want to take a look.

Greg

[tezza]

Greg,

Good write up. I'm curious to what happened?

The logic analyser looks useful! I'm not sure I'd have the skills to interprate the output even if I had one but it would seem to beat using my $12 Jaycars logic probe!

[Gibsaw]

Eww..don't you hate that. Broken stiff multiwire ribbon cables can be a bitch to fix. Not impossible though. Strip back the wire and solder.

It's times like this you need (and I have) an all-in-one combined soldering iron / solder sucker very similar to this... You'll never ever look back.

[gnewtonaus]

I finally got the SVI-328 MkII working! Turns out it was a few bad DRAM chips.

Check out the complete updated story with lots of info and pics at https://sites.google.com/site/walztroni ... i-328-mkii

[lizardb0y]

I finally got the SVI-328 MkII working! Turns out it was a few bad DRAM chips.

Check out the complete updated story with lots of info and pics at https://sites.google.com/site/walztroni ... i-328-mkii

Congratulations!

Thanks for doing such a good write-up of your diagnostic process. I'm sure someone else will find it helpful. I'm considering getting the OpenBench Logic analyser myself

--
Andrew

[tezza]

Well done! It's great to see an old machine come back to life. It's also great to see such a detailed write-up of the step-by-step diagnostic process. I'd read about the Openbench logic analyser and felt it would be a good thing to have.