EEVblog Electronics Community Forum

EEVblog => EEVblog Specific => Topic started by: EEVblog on September 12, 2019, 10:28:30 pm

Title: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: EEVblog on September 12, 2019, 10:28:30 pm
Can you find the fault in the IBM PCjr wireless keyboard before Dave does?
A most excellent adventure in troubleshooting.

https://www.youtube.com/watch?v=9inGSp2QnfI (https://www.youtube.com/watch?v=9inGSp2QnfI)
Title: Re: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: SparkyFX on September 13, 2019, 02:11:29 am
Wow, the logic chip testing feature in the device selection dialog of the MiniPRO, either forgot or overlooked it. Thanks for showing and pointing out that failure mode of the capacitor.

That keyboard needs some cleaning as well :D
Title: Re: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: poot36 on September 13, 2019, 03:31:34 am
Around the 8:22 mark on your video what is the bubbly liquid that drops on to the ESD mat?
Title: Re: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: NivagSwerdna on September 13, 2019, 04:23:23 pm
It appeared that the C was OK when tested with the DE-5000 LCR meter.... this is a bit worrying since I tend to use that device when repairing things... tell me more...
Title: Re: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: Kleinstein on September 13, 2019, 05:32:46 pm
The cap tester may not check for leakage.  With an electrolytic cap this leakage could be current for reformation of the oxide layer. So there is a slight chance that just leaving the circuit powered for some time could have fixed the problem.
Title: Re: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: SparkyFX on September 13, 2019, 09:47:29 pm
Quote from: Kleinstein on September 13, 2019, 05:32:46 pm
The cap tester may not check for leakage.
Got a quite similar one, from what i read in the manual, it tests with 0.6Veff and runs AC tests (C,ESR, D, theta) in serial mode.
Measuring Rp in parallel could do the job if i got it right, but probably not at 6V and without knowledge of typical comparison values. So questionable if it can show "leaky" caps without other symptoms?

Quote
So there is a slight chance that just leaving the circuit powered for some time could have fixed the problem.
The CMOS input probably does not feed/draw enough current for this self healing to happen. Would need to ground the input artificially for the time.
Title: Re: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: orion242 on September 14, 2019, 02:40:17 am
Quote from: poot36 on September 13, 2019, 03:31:34 am
Around the 8:22 mark on your video what is the bubbly liquid that drops on to the ESD mat?

Lol, spit.  Dave must be foaming at the mouth, rabies from his outback adventures!
Title: Re: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: wilfred on September 14, 2019, 02:43:07 am
Quote from: orion242 on September 14, 2019, 02:40:17 am
Quote from: poot36 on September 13, 2019, 03:31:34 am
Around the 8:22 mark on your video what is the bubbly liquid that drops on to the ESD mat?

Lol, spit.  Dave must be foaming at the mouth, rabies from his outback adventures!

Australia is free of Rabies. Dave must have been foaming at the mouth for other reasons.
Title: Re: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: orion242 on September 14, 2019, 02:46:59 am
Quote from: wilfred on September 14, 2019, 02:43:07 am
Australia is free of Rabies. Dave must have been foaming at the mouth for other reasons.

Australian Bat Lyssavirus!!

He's always talking about bat $hit, must be near them.
Title: Re: EEVblog #1245 - Most Excellent IBM PCjr Keyboard Repair
Post by: Per Hansson on September 14, 2019, 06:46:22 am
Would be fun to see the Vloss indicated by your cheap component tester (EEVblog #1020) of that leaky capacitor.