Recapped Macintosh Color Classic AB now making Ticking Sound & Fluctuating Voltages

[lfletche]

Hey everyone, hoping someone can give me a steer on a problem I am facing since recapping my Colour Classic Analog Board. It was working OK beforehand, but I decided to do some preventative work on it and replace the caps. After recapping all recommended caps (as per the Recap-A-Mac guide) this is the issue I am now facing - the board now makes a ticking sound & both the 5V & 12V voltages are fluctuating and not stable.

I've gone over my work a few times and double & triple checked everything - I also swapped all caps again and reverted it fully back to all the original caps as part of my troubleshooting and the fault still persists now even with the original caps that did work beforehand. So I've clearly broken something along the way.

Here is a shot of the top of the board:

Also a shot of the bottom of the board - note that I had to do some creative trace work near RF20 due to damaged traces that have come off the board due to heat damage. I basically used the legs of the 220uf 35VC capacitor to connect to where the trace was meant to go - all checks I've done seem to check out OK:

With the board removed from the body of the Mac I have recorded this video which demonstrates the fault - both the noise as well as the voltage fluctuating:

Running the board in the case with the CRT and logic board connected basically produces the same result - the Mac starts to do a chime but then stops half-way through because the voltages are all over the place.

Has anyone seen this kind of fault before and able to offer some suggestions on places I should be looking to troubleshoot? Any help you can offer would be greatly appreciated!

Thanks,
Luke.

 

[68Krescue]

Hey Luke- I just saw your post and wondered if you gave it a good alcohol scrub. If not, try spraying it down with 91% isopropyl (or higher), scrub the board and components gently with a toothbrush then blow it dry, preferably with an air compressor. Hope this helps. Good luck!

 

[lfletche]

Hey, I had cleaned up the flux I used with isopropyl locally in the areas I was working on..... but it's a good point. I haven't tried giving it a good scrub as you have suggested here. I've now done that this afternoon and I have the AB air drying. Will give give it a good going over with the air compressor tomorrow and then try it again and let you know.

 

[68Krescue]

Ok hopefully that'll do it. Letting it air dry is ok too, but I prefer shooting compressed air on the wet board and components to blow the alcohol all around, especially in those hard to reach places.

 

[lfletche]

So I finally got this Analog board to stabilise. After getting my hands on another one I was able to do some comparisons. What I have discovered is these boards really do not like to run without any load on them and if you do run them like what I did in that video you see the voltage fluctuations like that and it then seems to take them a while to return to normal behaviour.

In the end how I fixed it was to run it in the machine with the CRT attached but no logic board inserted - the ticking slowly stopped and the voltages while fluctuating around were not as severe. Then powering it on with a CC logic board the voltages stabilised and the machine boots. Now if I power it with the logic board removed again I get a rock solid 5/12V.

The second analog board I secured was really dirty so I gave it a good clean as per what @68Krescue said above. After getting it all looking nice and clean I saw the exact same voltage fluctuations with this board as well - I followed the same process again and it has now also returned to stable voltages.

I’m not sure I fully understand it. But I am glad I’ve got it working again and know how to solve the issue hopefully in the future.

 

[68Krescue]

Glad to hear you got your Color Classic running again!! Thanks for sharing your experience.

 

[Mu0n]

Thanks a lot for sharing that. After a few days of pristine working days, summer time was awful to my Japanese bought CCII and I can't get the CRT to energize anymore. I'll try your trick and test things out thoroughly.

I bought a better multimeter (Kaiweets just like yours!) and I'm waiting for it
I bought a scope (rigol 200 MHz, big splurge) and I'm waiting for it.