Advice needed...Please help!!

[antony c]

Hi all!
Im new to this forum, but not new to the Commodore scene.
Ok, a little background on me...

I originally was bought my first C64 in 1984 and was hooked. I went on to learn Assembly (even before BASIC, I think!!) and wrote a few unfinished games, and designed a SID based synth cart(just as CBM went wobbly!).

Anyway, roll on a few (i.e. 20) years, and I see on youtube the boing demo running on a friggin C64!! Then I see the Soundemon 4 channel sample demo, amongst other things, and decide to get back into the C64 scene. That machine is still going strong!

Ok, so Ive picked up a C128 and a 128D. The 128D looks like it has terminal rot on the PCB and wont power up, and the 128 looks clean. I then try to wire up the 128D PSU to the 128 with an old amiga lead, only to trip the main fuse box in my house! Oh dear!
I read the diagrams wrong and wired the input from the PSU end to the output from the computer end, so was connecting a mirrored image of what i should have.Lets just say the 128 is unresponsive now!So I have got hold of the SAMS comuterfacts for the 128, but Im a coder not an electronics guy, but Im going to have a go!!

I have a multimeter but what I need to know is can I get by with one of those cheap 'hobby' USB oscilloscopes (-5V to +5V), or will i need a better one for the 9VAC testing?  Also, as an aside  I need a front panel for my 128D, if I ever get it working, and a C128 PSU.Anyone have any spares?

Any advice would be most welcome. Thanks guys for taking the time to read my ramblings. Its taken me about an hour to type this correcting spelling typos and missing letters on an old rubbish Labtec wireless keyboard!! lol
I am going to plug a USB one in as soon as I finish this sentence!   

[Hydrophilic]

Wow!  If I understand correctly, you had the PSU backwards.  It normally steps down the AC mains from a few hundred volts to less than 10V.  But if you reversed it, then it would step up the voltage from a few hundred to a few thousand volts!  Needless to say, the circuitry in the C128 will not handle a few thousand volts...

If your lucky, something in the PSU blew up before the C128 was damaged.  First I suggest getting a new power supply.  If the Commodore doesn't work with that, it might be a nightmare... likely multiple components are blown.  You may be better off buying a new one.  I wouldn't want to work on it, and like working on electronics.

Well, good luck!

[antony c]

Hi,

I dont think it was quite that horrendous!
I basically crossed wires, so 5VDC ended up going to either GND or 9VAC and 9VAC went t GND or 5VDC or another combination similar t that.
I wasnt routing the wrong end of the transformer or anything like that! Still feel a bit stupid though! 

[Hydrophilic]

I dont think it was quite that horrendous!

That's good to hear.  You can use your cheap scope to check the voltage coming from the PSU is still good.  I'm suprised your home's circuit breaker tripped before the fuse in the PSU blew out... or maybe somebody by-passed the fuse in the PSU?

If you ran 9VAC or 5V DC to ground, the C128 may not be damaged.  But if you ran 9VAC to the 5V DC then you may have problems, as most TTL chips have an absolute maximum rating of 7V DC.

Well once you know the PSU is giving good voltage (obviously replace it or try to fix it if not), then you can try out the C128 and see if it works.  If it doesn't then your next step depends on the symptoms.  You might find this useful...

As always, Ray Carlsen's repair articles to the rescue, specifically "C128: chips vs symptoms and diagnostics".

[antony c]

Thanks for the tips. Ive already scoured the net for C128 info, and Mr. Carlsens name has popped up many times!
However, Im not sure the C128D PSU is 100%, and I really dont want to open it up, as Im not really an electronics pro. If I could at least find someone who is selling a working PSU (either one will do for now, 128 or 128D) then at least thats a starting point. If the machine doesnt work, I can then test for low voltage signals on the mainboards rather than risk my life with the PSU!

I dont suppose anyone has any of these PSU's new or refurbished?

[RobertB]

...Mr. Carlsens name has popped up many times!
However, Im not sure the C128D PSU is 100%, and I really dont want to open it up, as Im not really an electronics pro.

Ray Carlsen would repair a C128D p.s..

          Truly,
          Robert Bernardo
          Fresno Commodore User Group
          http://videocam.net.au/fcug

[antony c]

I may well ask him nicely to repair.However, I dont like hassling anyone unless its absolutely necessary (i.e. I cant do it myself), and besides I will need to buy at least one PSU anyway. Was hoping someone local (UK) had some spares.
What I think I will do, is get hold of one of them cheapy (~£50) oscilloscopes and see exactly what this 128D PSU is putting out, and then decide from there if I want to repair a corroded 128D or a possibly blown 128.At least I can figure how many (if any!) PSU's I will need!
Right, so I take it I will need a 'scope that can measure at least up to 9VAC/DC with maybe up to 5Mhz speed?

[RobertB]

I may well ask him nicely to repair. However, I dont like hassling anyone unless its absolutely necessary...

It would be no hassle for Ray.  That's what he's in the business for... to repair Commodores.

          And he has repaired for overseas customers,
          Robert Bernardo
          Fresno Commodore User Group
          http://videocam.net.au/fcug

[antony c]

Im sure if I sent him what needs repairing here, I would have to take out a hefty loan!
And considering that Im coming up to the 'financially drained' part of the year, I think I will have a go myself...
If it was definitely just the PSU, then maybe its a good option, but I really need to see whats broke here, as it may be cheaper to buy another C128 than to have these 2 repaired.

And anyway, Ive got a few C64's hanging around with minor faults. It would be good for me to pick up some electronics knowledge!

If it all fails miserably, you can be sure Ray Carlsen will be approached!