ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 [2] 3  All   Go Down

Author Topic: Question for the experienced bench techs  (Read 3151 times)

Hayden J. Nebus

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 637
  • Richmond, VA
Re: Question for the experienced bench techs
« Reply #10 on: June 17, 2018, 09:59:41 PM »


JR described a number of issues.  But to add, for gear that pulls to much current is to use an ohm meter (in the diode test position) to test all the diodes and normal transistors.  I can't begin to count the number of hours looking for shorted parts that way.

Diode scale is like the Swiss-army setting on a DMM! Continuity, shorts, capacitor polarity, capacitor leakage, transitor leg orientation, the list goes on... Oh yeah, diodes too!
Logged

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3381
  • Isle of Wight - England
Re: Question for the experienced bench techs
« Reply #11 on: June 18, 2018, 04:53:09 AM »

And then you have the intermittants.

Meaning it works perfectly every time you have it in to look at it but goes wrong every time you give it back to the customer!


Steve.
Logged

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 9534
  • Atlanta GA
Re: Question for the experienced bench techs
« Reply #12 on: June 18, 2018, 07:28:40 AM »

Meaning it works perfectly every time you have it in to look at it but goes wrong every time you give it back to the customer!


Steve.
I worked for a guy once who told the customer to take a picuter of him and put it under the lid of their VCR.

That way the electrons inside the VCR would "behave" because a tech was looking at them.

TRUE STORY.  He could not find the intermittant (he was a very good tech) and just gave up.
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 17176
  • Hickory, Mississippi, USA
    • Resotune
Re: Question for the experienced bench techs
« Reply #13 on: June 18, 2018, 09:26:01 AM »

Diode scale is like the Swiss-army setting on a DMM! Continuity, shorts, capacitor polarity, capacitor leakage, transitor leg orientation, the list goes on... Oh yeah, diodes too!
Some of us old timers will recall before we had DMM and fancy diode scales. The old school Simpson 260 could check diode/transistor junctions using the ohms scale...

I suspect modern DMMs could too but dedicated diode scale is better.

JR
Logged
Cancel the "cancel culture". Do not participate in mob hatred.

Chris Hindle

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 2693
  • Montreal, Quebec, Canada, Earth, Sol System,......
Re: Question for the experienced bench techs
« Reply #14 on: June 18, 2018, 12:19:29 PM »

Some of us old timers will recall before we had DMM and fancy diode scales. The old school Simpson 260 could check diode/transistor junctions using the ohms scale...

I suspect modern DMMs could too but dedicated diode scale is better.

JR
Jeez, that brings back memories.
I still have my 260 - somewhere..
Pulled the batteries, but didn't have the heart to bin it.
Chris.
Logged
Ya, Whatever. Just throw a '57 on it, and get off my stage.

Frank Koenig

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1318
  • Palo Alto, CA USA
Re: Question for the experienced bench techs
« Reply #15 on: June 18, 2018, 12:27:12 PM »

I suspect modern DMMs could too but dedicated diode scale is better.

Modern DMMs are specifically designed NOT to turn on P-N junctions in Ohms mode unless using the diode setting. This is to allow in-circuit testing of connections and passives. A great innovation, I think.

As to intermittent problems, there has been a standing joke among my friends (for decades) that I possess the "laying on of hands". Whenever someone brings me some broken thing and I lay my hands on it it starts working. Of course when I send something to a shop to get fixed it starts working, too, more often than not. This leads me to think that another aspect of trouble shooting is thinking in terms of setting traps for intermittent problems. Digital scopes, data logger, buzzers with alligator clips, etc.

--Frank
Logged
"Nature abhors a vacuum tube." -- John Pierce, Bell Labs

Frank Koenig

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1318
  • Palo Alto, CA USA
Re: Question for the experienced bench techs
« Reply #16 on: June 18, 2018, 12:39:55 PM »

I still have my 260 - somewhere..

I've got one sitting on my bench right now with leads attached ready for action. But I confess I don't use it much.  -F
Logged
"Nature abhors a vacuum tube." -- John Pierce, Bell Labs

Frank Koenig

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1318
  • Palo Alto, CA USA
Re: Question for the experienced bench techs
« Reply #17 on: June 18, 2018, 12:46:30 PM »

Frank are you a pilot?

Hi Scott, FAA still thinks I'm a pilot. I have my doubts sometimes. I'm going to fly more next year -- really, I am, really. -F
Logged
"Nature abhors a vacuum tube." -- John Pierce, Bell Labs

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2672
Re: Question for the experienced bench techs
« Reply #18 on: June 18, 2018, 01:03:39 PM »


As to intermittent problems, there has been a standing joke among my friends (for decades) that I possess the "laying on of hands". Whenever someone brings me some broken thing and I lay my hands on it it starts working. Of course when I send something to a shop to get fixed it starts working, too, more often than not. This leads me to think that another aspect of trouble shooting is thinking in terms of setting traps for intermittent problems. Digital scopes, data logger, buzzers with alligator clips, etc.


I've fought my share of "intermittents" in industrial electronics-but I have to ask, are there any really, truly intermittents?  The laws of physics are never intermittent-so there is always a cause-the trick is finding the root cause-be it vibration, thermal, radiation or whatever.
Logged
Steve Swaffer

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 17176
  • Hickory, Mississippi, USA
    • Resotune
Re: Question for the experienced bench techs
« Reply #19 on: June 18, 2018, 01:22:42 PM »

I've fought my share of "intermittents" in industrial electronics-but I have to ask, are there any really, truly intermittents?  The laws of physics are never intermittent-so there is always a cause-the trick is finding the root cause-be it vibration, thermal, radiation or whatever.
For analog circuitry I agree and age old techniques to parse out intermittence include cold spray (to force thermal stress), and percussive (tapping) troubleshooting for mechanical stress. OTOH modern digital circuitry can get into what appear to be intermittent states from combinations of flawed software, and or obscure button press combinations. While technically this is deterministic, this can be very difficult to replicate.

I have one digital controlled appliance that can lock up under random powering up sequences. Almost impossible for me to troubleshoot (without access to code, boot-up circuitry, etc). I just leave it always powered up. (Life is short and I already fix enough of other product designer's mistakes.) 

A little like a couple of my GFCI outlets that randomly trip for no known reason. One likes to trip when power is interrupted. I don't know how to fix that, other than replacement, while I doubt the fault is from old age or stress.

JR

PS: A classic joke about percussive repair is that the repairman charges the big bucks because he knows where to smack it.  ::)
Logged
Cancel the "cancel culture". Do not participate in mob hatred.

ProSoundWeb Community

Re: Question for the experienced bench techs
« Reply #19 on: June 18, 2018, 01:22:42 PM »


Pages: 1 [2] 3  All   Go Up
 



Site Hosted By Ashdown Technologies, Inc.

Page created in 0.033 seconds with 19 queries.