|
Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
|
Thread Tools |
11th May 2019, 11:21 pm | #1 |
Dekatron
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,748
|
Avo EA113 faulty resistance range fixed - again
Almost exactly two years ago, I posted this Success Story and since then the instrument has given excellent service as my main workshop meter.
This week, a fault appeared, namely the loss of the 'ohms x 100' range. I studied the circuit diagram and homed in on R59 (10k) which on inspection had a very obvious dry joint at one end, shown by the white arrow in the attached picture. I re-soldered the joint and all was well again, but a little bell rang somewhere in the deep recesses of my memory that I had done this before. Sure enough, I had re-made this same joint exactly two years ago, and I mentioned it in the original posting. I can't explain why this joint has failed again. I'm not known for making dry joints. Perhaps there is some residual contamination present which led to the joint failing? I will put a note in my diary to open the meter up in May 2021 and check it again! Phil
__________________
Phil Optimist [n]: One who is not in possession of the full facts |
12th May 2019, 5:45 am | #2 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,614
|
Re: Avo EA113 faulty resistance range fixed - again
Very odd. I must open mine and see if there’s any evidence of a similar problem.
The only thing I can surmise is that it may be a heat related problem, if the resistor warms, expands and then contracts it may disturb the solder.
__________________
Richard Index: recursive loop: see recursive loop |
12th May 2019, 7:09 am | #3 |
Dekatron
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,748
|
Re: Avo EA113 faulty resistance range fixed - again
Morning Richard. Yes, that’s a valid suggestion under normal circumstances, and the solder does indeed appear to have flowed away from the component leg back towards the pool, but in this location the resistor is dissipating virtually no power. It’s very odd, but it’s easy enough to keep an eye on. Fortunately this resistor is easily accessible, unlike so many other components...
Did you manage to make any progress repairing your faulty EA113s? ISTR you have one working example and two faulty ones.
__________________
Phil Optimist [n]: One who is not in possession of the full facts |
12th May 2019, 7:20 am | #4 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,614
|
Re: Avo EA113 faulty resistance range fixed - again
Hello Phil,
Unfortunately my stash of EA113s is still the same - one working and in fairly constant use, one with a faulty AC or DC, I don't remember which, and one that is quite dead. I have been diverted by a number of other 'projects' - the Gould DSO took a lot of time, and now I have a Radford LDO3 on the bench with an intermittent fault. I will have a look at my EA113s and see if the same resistor exhibits any solder issues.
__________________
Richard Index: recursive loop: see recursive loop |
12th May 2019, 7:24 am | #5 |
Dekatron
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,748
|
Re: Avo EA113 faulty resistance range fixed - again
Happens to me, too, all the time! Good luck,
__________________
Phil Optimist [n]: One who is not in possession of the full facts |
12th May 2019, 7:35 am | #6 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,902
|
Re: Avo EA113 faulty resistance range fixed - again
Any other joints looking iffy?
It must be quite difficult to get any heat into a 10k resistor with only 4 AA cells to go at. You don't have a goblin infestation problem you haven't noticed? Tiny hands, tiny soldering irons and an unfriendly sense of humour... Good mystery, Phil. Our equivalent to a locked-room Agatha Christie. David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
12th May 2019, 10:11 am | #7 |
Dekatron
Join Date: Aug 2016
Location: Colchester, Essex, UK.
Posts: 4,108
|
Re: Avo EA113 faulty resistance range fixed - again
Out of all the yards of solder we use, i suppose there will be the occasional inch that is short on rosin.. Or a duff reel that has less Pb in it than the label declares..Mixing that with older solder could move the %age of Pb into the 'bad' zone?
Dave |
13th May 2019, 9:38 pm | #8 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,614
|
Re: Avo EA113 faulty resistance range fixed - again
Here's photos of the same resistor on my three EA113s, none seem to have a problem with the solder (in order, working, faulty, dead):
__________________
Richard Index: recursive loop: see recursive loop |
14th May 2019, 10:59 am | #9 |
Dekatron
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,748
|
Re: Avo EA113 faulty resistance range fixed - again
Certainly no visible problem with the soldering there. Mine had a visibly obvious dodgy joint. As David says, one of life’s mysteries, of which when dealing with Avos there are many.
__________________
Phil Optimist [n]: One who is not in possession of the full facts |
14th May 2019, 2:52 pm | #10 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,614
|
Re: Avo EA113 faulty resistance range fixed - again
I wonder if the rivet is giving a problem? Mine seem to have through-hole rivets a bit like some Philips machines, in the Philips CD players (104?) there's a well-documented issue where the rivet develops a dry joint to the print....
__________________
Richard Index: recursive loop: see recursive loop |
14th May 2019, 4:37 pm | #11 |
Dekatron
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,748
|
Re: Avo EA113 faulty resistance range fixed - again
Hard to see a rivet on my example, but the range board is quite thick and double-sided so it probably does have rivets.
I know some problems did arise many years on with the early plated-through holes on some PCBs in 1970s gear too.
__________________
Phil Optimist [n]: One who is not in possession of the full facts |
15th May 2019, 7:42 pm | #12 |
Octode
Join Date: Jul 2004
Location: Dundee, UK.
Posts: 1,813
|
Re: Avo EA113 faulty resistance range fixed - again
Phil's original picture shows a fibreglass board while Richard's pictures show two SRBP and one fibreglass board of a different type to Phil's. It seems probable that these different materials may be used with different connection techniques which might be significant.
PMM |
15th May 2019, 10:16 pm | #13 |
Dekatron
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,748
|
Re: Avo EA113 faulty resistance range fixed - again
Peter, you’re absolutely right, and your keen eye has spotted the deliberate mistake... er, well, my mistake anyway. I uploaded the wrong picture in post #1. That was one I found whilst researching a couple of years ago. The actual picture of my meter is attached, together with a close-up of the repaired dry joint at the upper end of the 10k resistor.
My PCB is a conventional SRPB type and closer study shows that it definitely incorporates rivets for through-board connections. The instrument’s serial number is 1377. The glass fibre board must have appeared in later production. Phil
__________________
Phil Optimist [n]: One who is not in possession of the full facts Last edited by Phil G4SPZ; 15th May 2019 at 10:19 pm. Reason: Clarification |