Topic: sound problems

[simonfr]

I have a Commodore 128 (albeit in C64 mode) which has an issue with sound output. I had the C128 fired up yesterday with my favourite game, Spellbound, but the sound output it 'bitty' and crackly

Its hooked up to a Commodore 1801 monitor through the video (5 pin DIN Plug) port. I know its not the monitor, or the 5 pin DIN lead, as i also have a Commodore 16 alongside, ant the combo works fine.

So my question to your good folks is...... I havent opened up the computer, but assume it could be the port connector itself, or perhaps compromided PCB tracks or dry solder joints.
How easy do you guys think it would be to fix, or is there someone in the UK who could repair the PCB/Soldering etc?

Cheers,

Simon

[Hydrophilic]

If you think it may be the connector, the easiest thing to try first would be some contact cleaner.  Spray a bit on the 5-pin DIN plug then insert/remove the connector several times with the power off.  Give it 30 to 60 minutes for it to dry up, then power on and give it a try.
 
Your guess of cold solder may be right.  Not difficult to touch-up solder points -- once you get the metal shield removed!  The shield comes in two parts (covering the top and bottom of the main PCB).  It has several tabs that are bent that need to be straightened so the shield can be removed, but they are also soldered.  So you got to remove the solder from the tabs, unbend them, and then you will probably find more solder that will need to be removed.  Their are about a dozen tabs, as I recall!  Not really difficult, just time-consuming.
 
I don't know anyone in the UK, but hopefully somebody else here does.

[RobertB]

I havent opened up the computer, but assume it could be the port connector itself...

     I would think that the port connector is bad.

          Back from yesterday's TOGA meeting,
          Robert Bernardo
          Fresno Commodore User Group
          http://videocam.net.au/fcug
          July 28-29 Commodore Vegas Expo v8 -
          http://www.portcommodore.com/commvex

[simonfr]

Hi guys, Thanks for the replies.

I'll take the cover off and give it a continuity check where i can following the tracks from the IC's and through the connector. Hope its straightforward otherwise i might need a nice shiny new soldering iron!!
I'll let you know how i get on...

Cheers
Simon

[simonfr]

Right...  I've opened it it and had a quick look at the board and there is nothing obvious except perhaps one cracked capacitor. Swung through a few of the tracks with a multimeter, and there seems to be continuity on the solder joints so far.
Anyway, I now have a full printout of the schematics. Does anyone have a picture of the board which identifies the main components for reference? I.e with overlaid text boxes for instance?

Cheers

Simon

[Hydrophilic]

I don't have a photo, but I did find the this image in the C128 Internals Book 1.  It seems about right, except that I remember the SID being on the left side of the Video Chips (and not the right side as shown).  It's been a while since I opened one, so it could be bad memory or changes in production...
 
Maybe it will help.  Hopefully the SID isn't defective.  It happens, and it may be the most expensive chip to replace.

[simonfr]

Cheers Hydrophilic!
That's just the ticket...  I did download quite a few things from the library including the Internals handbook, but must have missed that!
:-)