Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #21   Report Post  
Old October 12th 18, 01:36 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jun 2012
Posts: 1,635
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

"The grease has dried out..."

I guess now would be a good time to dispel this old husband's tale.

When the union between heatsink and transistor is undisturbed, dried out grease that is like cement is perfectly fine. I have conducted a few studies on it albeit subjective. That is that the temperature difference between a transistor and the heatsink to which it is mounted is not significant, AS LONG AS IT IS NOT DISTURBED.

That assumes it was installed properly in the first place.

First of all you never spread the compound, you put a dab or a bead where it will be squished out as it is tightened. this eliminates air pockets. If you have a big air pocket between there you would be better off with no compound at all.

Granted, the old dried out compound does not have as good thermal conductivity as nice new wet goop, but it is seated over the years and works quite well. If you doubt what I say take a meat thermometer and check the case of a TO-3 and its heatsink on one that has been there for decades and ne that you remount with new goop now. In fact to make sure there is no error, clean those surfaces with "things". Scrub pads, alcohol, maybe acetone, and finish with a coffee fitter to get the surface nice and smooth. Apply a dab or bead right where the ounting will exert the mos even force, on a TO-3 for example, that will be about in the center and it is normal for some of the goop to squeeze through the holes for the pins. then get that thermometer out after using the unit to get the heat up, like on a stereo amp, run both channels at like 1/3rd power for an hour, that'll warm er up. As soon as you detect heat, measure. It has JUST been produced so it is still conducting to the heatsink. That would be the most accurate comparative test, but not for absolutes. It is not a number except for "how much" one is better than the other. Your actual calories of heat/watts dissipation and all that **** matters not. Iti s simply better or worse. Try it.

  #22   Report Post  
Old October 12th 18, 02:01 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Mar 2007
Posts: 1,335
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

An infra-red heat gun is better at very close range. It will show variations of fractions of a degree.

Also very good for pinpointing hot-spots. Within a couple of inches, the spread is 1/6" for a standard 12:1 unit. There are narrower devices, but they are comparatively pricey.

Peter Wieck
Melrose Park, PA
  #24   Report Post  
Old October 12th 18, 03:19 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jun 2017
Posts: 322
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Friday, October 12, 2018 at 8:36:35 AM UTC-4, wrote:
"The grease has dried out..."


I guess now would be a good time to dispel this old husband's tale.

When the union between heatsink and transistor is undisturbed, dried out grease that is like cement is perfectly fine.


You beat me to it. It's not the liquid component of heat sink compound that transfer heat, it's the solids that are suspended in the goop. The compound may get hard, but the solids are still packed between gaps doing their job.


  #25   Report Post  
Old October 12th 18, 04:27 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Sep 2006
Posts: 612
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On 10/12/2018 10:19 AM, John-Del wrote:
On Friday, October 12, 2018 at 8:36:35 AM UTC-4,
wrote:
"The grease has dried out..."


I guess now would be a good time to dispel this old husband's tale.


When the union between heatsink and transistor is undisturbed,
dried out grease that is like cement is perfectly fine.


You beat me to it. It's not the liquid component of heat sink
compound that transfer heat, it's the solids that are suspended in
the goop. The compound may get hard, but the solids are still packed
between gaps doing their job.


Provided they're really undisturbed. Thermal cycling can cause
delamination problems that don't occur with the oil present.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
https://hobbs-eo.com


  #26   Report Post  
Old October 12th 18, 08:19 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Mar 2007
Posts: 1,335
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Friday, October 12, 2018 at 9:24:31 AM UTC-4, Phil Hobbs wrote:

Providing that the thermal infrared emissivity of the surface is high,
e.g. plastic or glass. A dab of grease or some tape will make it work a
lot better.


I have not experienced that issue, for the record. What I find is that accuracy starts to suffer as the battery gets weak. I view them the same as smoke-alarm batteries - 2x per year, whether I need it or not. And the used batteries are put aside for my increasing number of novelty radios that the grandkids are fighting over. Not in them, but with them for demonstration purposes.

Peter Wieck
Melrose Park, PA
  #29   Report Post  
Old October 16th 18, 07:19 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Mar 2007
Posts: 1,335
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Tuesday, October 16, 2018 at 1:03:31 PM UTC-4, Phil Hobbs wrote:

Your accuracy requirements aren't high, then. A shiny metal surface can
easily show up as 90% room reflection and 10% surface emission. A bit
of tape will reverse those numbers.


Perhaps not. 90% of the use is to verify that I am not looking at a freeze-out on an AHU coil or at the discharge temperature of a chiller. And in such cases, it is pretty much go/no-go. I am not the mechanic, but I have learned over the years that "trust but verify" does not only apply to the former Soviets.

But, for 10% of the use, it is to let office workers, docs or other staff know the temperature in their space. The docs have, on more than a few occasions, pulled out a thermometer of their own - and so far, they and my little heat gun have agreed.

On rare occasion, I will use it at home to verify radiator temperature against the gauge on the boiler, or to look for hot-spots in some bit of audio or radio equipment, or other. And, if one tube on an output pair is acting differently from another, I understand I have an issue.

Peter Wieck
Melrose Park, PA
  #30   Report Post  
Old October 16th 18, 08:35 PM posted to sci.electronics.repair
external usenet poster
 
First recorded activity by DIYBanter: Jun 2012
Posts: 1,635
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

"Provided they're really undisturbed. Thermal cycling can cause
delamination problems that don't occur with the oil present. "

What I consider the better TO-3s are aluminum, not steel. Another advantage is that they won't bend as much if the mounting surface is not perfectly flat.

T


Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Harman Kardon Citation 17 Pre-Amp One Channel Intermittent [email protected] Electronics Repair 27 April 1st 18 07:55 PM
Harman Kardon FM100 - early version? - Harman-Kardon Model FM-100 Centerpoint.pdf (0/1) legg Electronic Schematics 4 August 6th 12 01:48 PM
Harman Kardon FM100 - early version? - Harman-Kardon Model FM-100 Centerpoint.pdf (1/1) legg Electronic Schematics 0 July 30th 12 07:59 PM
Harman/Kardon Receiver AVR-75 channel out Steve Electronics Repair 3 June 14th 05 02:53 AM
Harman/Kardon HK3370 Tuner Hum Robert Nogo Electronics Repair 3 January 1st 04 08:09 AM


All times are GMT +1. The time now is 11:56 PM.

Powered by vBulletin® Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright 2004-2019 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"

 

Copyright © 2017