Strange buzzing, distorted picture followed by corruption

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cheshirenoir
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Strange buzzing, distorted picture followed by corruption

Post by cheshirenoir » Wed Jun 15, 2022 1:36 pm

Hey Folks,
My Wizzard has started playing up again. Every time I think I have this tamed, it happens again.
After an indeterminate amount of time (Sometimes seconds, sometimes hours) it starts to make a buzzing noise, the picture distorts and eventually the program corrupts. Sometimes knocking it(!) fixes the problem.
I've:
  • Replaced the 7805 and 7812.
  • Removed a possible short. (Tin whisker)
  • Improved the earth plane connection on the underside.
  • Reflowed every suspect solder joint.
  • Checked voltages on the RAM. (they looked fine)
  • Replaced the on off switch.
Before I start blindly desoldering things, anything I should be concentrating on? Any areas known to be problematic? I can get an oscilloscope on to it easily enough...

(I want to work on a new project, so having it working again would be good)

Cheers!

Chesh
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cheshirenoir
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Re: Strange buzzing, distorted picture followed by corruption

Post by cheshirenoir » Fri Jun 17, 2022 1:01 am

OK at this point I'll check the caps around the power supply, then look at the RAM, then the 9929.

Chesh
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Scouter3d
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Re: Strange buzzing, distorted picture followed by corruption

Post by Scouter3d » Fri Jun 17, 2022 4:59 am

Hi Chesh,

sadly i have no good ideas...

you could try using "cold spray" find the faulty component, spray one component at a time, when the console starts to act weird and see if it changes behaviour...

Cheers, TOM:0)
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cheshirenoir
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Re: Strange buzzing, distorted picture followed by corruption

Post by cheshirenoir » Fri Jun 17, 2022 6:21 am

No worries :-)
Was mostly asking in case it was something that "everyone" got that I wasn't aware of. (On the Commodore 64, for instance, it's ALWAYS the PAL chip that fails)
I'll treat it as a "normal" problem and try and attack it at the logical spots.

Chesh
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Scouter3d
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Re: Strange buzzing, distorted picture followed by corruption

Post by Scouter3d » Fri Jun 17, 2022 9:42 am

Yes, i think i can change a C64 PLA blindfolded after all the faulty ones i have encountered :0)
Good luck with the fault-finding :0)

TOM:0)
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cheshirenoir
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Re: Strange buzzing, distorted picture followed by corruption

Post by cheshirenoir » Sun Jun 26, 2022 8:04 am

I think it's fixed. Tapped around with a non conductive probe, and the fault seemed to be with the big 8200𝜇F capacitor.
I replaced it, and while I was there I spotted what may have been a dry joint under another capacitor in the area.
Either way, the buzzing seems to have gone away.

Currently trying one more attempt to use conductive ink to fix the controller. After that I can give it a proper test.

Chesh
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Scouter3d
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Re: Strange buzzing, distorted picture followed by corruption

Post by Scouter3d » Mon Jun 27, 2022 9:08 am

Glad you could fix it! Now one of my CVs has started to sporadicaly not work... will look into it... :0)
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cheshirenoir
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Re: Strange buzzing, distorted picture followed by corruption

Post by cheshirenoir » Fri Jul 15, 2022 1:27 pm

Aw man! Good luck fixing it. IF you get distortion like I did, check around the PSU.

Chesh
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