Who's gonna save my nicely bent SK-1 ?

[alienized]

Hi there,

I started playing with a LTC1799 module yesterday and only bad things happened to me from there...

I could't make it work on a PT-88 so I tried to install it on my already nicely bent SK-1, working like a charm.

I followed GetLoFi instructions and wiring diagram and first it just worked perfectly. I was amazed by the sounds it produced !
I wanted to make better solder joints so I turned the SK-1 off and resoldered the two wires that allow to switch between original clock component and the LTC module.

When I turned the SK-1 on again, not a sound. Then I noticed that the led stayed on even on the "off" position. I tried to switch it on and off, unplugged the power supply, tried it with batteries, switched on and off again for several minutes... Nothing.

And still the led is on whenever I plug the power supply or put batteries...
(I must confess I left the power supply plugged to the SK-1 when resoldering; however the power was off)

I haven't tried to discharge the capacitors yet (I just need to connect both pins, no precautions whatsoever like with a big 110/220V amp?...) but I'm not very optimistic. Any clue? Where should I start looking ?
I must say I have another working SK-1 so I can try exchanging components (well, maybe not the main IC... I hope the problem isn't in there !)

After that (yes you can say I'm stupid...) I tried to connect the LTC module to my PT-88 again (the one that still worked, not the one I damaged yesterday and has now very low volume, see my other post) following the same diagram. And guess what ? It also stopped working. No sound when volume on positions 1 & 2, a big nasty noise when on positions 3-5...

After this I checked voltages coming out of the LTC module to see if it could fry something but it never goes above 3V (at least that's what my voltmeter reads, but it has no peak function).
I noticed that some of the caps have a greeny sticky thing that holds some of them together but I don't think this is leakage as they are not swollen or anything.

Thanks in advance for your help and tips : your posts will keep me out of depression.  

[Circuitbenders]

Either leave the SK off for a few days or short the pins of that big cap near the power input, it won't hurt you.

You can't get a reliable measurement of the output of the LTC with a multimeter as its not fast enough. You'll probably get a rough average between 0 and 5v, i.e. about 2-3v or so.

This may seem obvious but have you checked, checked again and then checked on more time for solder bridges and track breaks etc etc? It pays to suspect hardware problems before you assume its an electronic problem. Check with the continuity tester on your meter that everything is still actually connected, i.e. is the coil leg still attached to whatever pin of the CPU its meant to be wired to etc.

If your LTC circuits are killing everything you try to attach them to, it might be pretty safe to assume that you might want to use a different circuit. Theres no real way to be sure whats going on without a scope.

That sticky stuff is just glue that holds things in place.

[alienized]

Thanks for your advice.
I uncharged the big cap (it gave something around 0.2v before that) but nothing changed.
I checked the connections and joints around the coil (where I worked) but everything is properly connected.
The power led still stays on all the time. When I switch from "off" to "on", the speaker doesn't even make a small "pok" ; it's absolutely silent, without a single hiss or parasite when volume to its maximum...
Could a defective coil do that ? (although I doubt it could have been damaged).  How do I test it ? Any other ideas ?...

[Circuitbenders]

Well, i'm no expert on the SK1 so all i can offer is general advice, but if theres no hiss or pop etc  then i guess that would suggest that its only the LED thats actually getting power and the amp / output sections aren't. I'd imagine there should be some hiss from the amp even if the CPU isn't starting up.

You might have something connected wrong on your LTC and you've been accidently grounding the power rails on stuff every time you connect the LTC. I take it you've checked that you're actually getting power to any of the IC's on the SK?

Could a defective coil do that ? (although I doubt it could have been damaged).  How do I test it ? Any other ideas ?...

Again, you'd need a scope to see it its actually ouputting anything.

[electoyd]

hi alienized
first up i would always check for solder bridges, esp after developing faults after opening it up.  Open it up again try taking your wires off and see if it works.  If it still does not work leave wires unconnected and take an (old) toothbrush rub it over the solder joints just make sure there is no solder bits short circuiting anywhere (make sure it is not one you will use again!).  Resolder any points you have touched if it is still not working it could even be a faulty ltc, i'm pretty sure they are vulnerable to voltage.  O/scopes are very handy but if you dont have one you can get software versions for PC but i've never used one, they are good for finding out whats going on in a circuit, i.e what area's are not getting power.

Important lesson if it works sometimes your best to leave it!

Your quite lucky because i happen to have a spare circuit board for an SK-1, well it's actually the 3 boards joined together.  I bought a box of casio spares years back amongst there was 6 circuit board skeletons in the box (no plastic cases just circuit boards) and one is an sk-1 this thing is dusty as hell and has been kicking about for 20 years with no real protection but seems in okay condition (all the connecting cables are in good condition).  If you pay postage on it you can have it, as i would rather see it getting used than more dusty, just email me i know how gutting it is when a fav machine karks it.

[electoyd]

hers a pic so you know i aint bullshitn u...................

[alienized]

GREAT !
I did more testing today : ICs are getting 5V. What I could do is test the amp section by injecting a sound signal before it. But where ?...
And the fact that it always stays lit isn't a good sign probably... Does anyone know what controls the power led ?