I've seen a this type of problem in the circuit boards of other
Tektronix equipment, this time it's afflicting two of my DM44s.

The problem is semiconductive and resides within the glass composite
of the board itself. I have identified two 1-5 megOhm instances or
resistance between unconnected (I made sure of this disconnection)
copper traces on the DM44 board and located in the A/D converter area
of the board. Freeze spray exacerbates the problem with some wild
resistance readings.

I had a 465 with the same problem in the time/div resistor network on
the timing board. There was this inability to properly calibrate the
instrument on a few time settings, the affected time settings were
related but after pulling resistor ends up for measurement I fould a
750kOhm resistance between completely disconnected traces. This scope
had never seen a soldering iron since the day it was produced and
showed absolutely no discoloration at or around the affected traces.
I gouged out a trough between the traces and viola! calibration
ensued without a hitch.

There are more than these two instances on this DM44 board, but at
this point I'm considering scrapping these 2 units because the work
involved in isolating this type of problem is not time effective. To
solve this type of problem requires scraping out the glass around the
affected trace.

My question is:
Has anyone had the same experience with the DM44 and found all the
defective areas on the board and/or is this problem related to age
and will it become wide spread? Please advise.
Thanks in advance, Mike at Baytekk Designs

Baytekk wrote:
I've seen a this type of problem in the circuit boards of other
Tektronix equipment, this time it's afflicting two of my DM44s.


...snippety for bandwidth..

My question is:
Has anyone had the same experience with the DM44 and found all the
defective areas on the board and/or is this problem related to age
and will it become wide spread? Please advise.
Thanks in advance, Mike at Baytekk Designs


Hi Mike,

well this problem I have seen with instruments used in industrial
areas. As far as I can say about it is a problem of the dirt covering
the boards. And, very interesting, it is most times NO VISIBLE dirt. I
asked chemist from the local university, and he just nooded : He said
that's often hapend due to certain sulfur and chloride chemicals that
contaminate these boards in electronic devices (sorry I forgot about
the full names of the chemicals).

In my situation this helped: thorough cleaning, comparable to the
dishwasher method Jim Yanik descreibes in the newsgroup (use a little
google time to find his articles).


Don't simply scrap the boards, some of the components (mostly
LD110/111 chips) are real hard to get nowadays (at least here in
europe)

hth,
Andreas

Thanks Andreas,

My frustration selected the word "scrap", my apologies, I would never
scrap these old DM44s I may "salvage" them, but only after I try one
last time to search-out & eradicate these resistance phantoms.

Thanks for the reminder on cleaning out the dirt, absolutely a must do
every time you "crack open" a new acquisition. I wish that was the
solution in this instance. I have a shelf full of specialized
chemicals & brushes for this.

The info from your chemist contact helps tremendously, sulfur &
chlorine compounds can be conductive and they can migrate through
certain mediums, like corrosion beginning at a battery terminal.
I looks like this type of contamination is initially very localized
and undetectable in QC yet migratory, and its only a matter of time
before it migrates through the board composite until it contacts a
couple of traces. This migration may take 20 years before it becomes
a problem from what I'm gathering here.

I have a few old Teks (a 453, four 465s, a 475 & the cadillac 485)
that are in beautiful condition. One 465 has one of my DM44s, the
thing is, is that this 465 has serial number B320864, this is near
the end of the production run for the 465 and I really want to keep
it as it was optioned (with the DM44). I could go on eBay & find
another "as is" 465/DM44 and swap out the boards, but I (as most
techs) would feel defeated by taking this route to solve a problem.
Yea, its personal. In the corporate world I would simply frizbee this
problem board.

My last ditch effort will be to unsolder all the components in that
area and begin ghostbusting. I did meet Bill Murray once a long time
ago at a party. LOL

Thanks again, Mike

lid (Baytekk) wrote in
:

Thanks Andreas,

My frustration selected the word "scrap", my apologies, I would never
scrap these old DM44s I may "salvage" them, but only after I try one
last time to search-out & eradicate these resistance phantoms.

Thanks for the reminder on cleaning out the dirt, absolutely a must do
every time you "crack open" a new acquisition. I wish that was the
solution in this instance. I have a shelf full of specialized
chemicals & brushes for this.

The info from your chemist contact helps tremendously, sulfur &
chlorine compounds can be conductive and they can migrate through
certain mediums, like corrosion beginning at a battery terminal.
I looks like this type of contamination is initially very localized
and undetectable in QC yet migratory, and its only a matter of time
before it migrates through the board composite until it contacts a
couple of traces. This migration may take 20 years before it becomes
a problem from what I'm gathering here.

I have a few old Teks (a 453, four 465s, a 475 & the cadillac 485)
that are in beautiful condition. One 465 has one of my DM44s, the
thing is, is that this 465 has serial number B320864, this is near
the end of the production run for the 465 and I really want to keep
it as it was optioned (with the DM44). I could go on eBay & find
another "as is" 465/DM44 and swap out the boards, but I (as most
techs) would feel defeated by taking this route to solve a problem.
Yea, its personal. In the corporate world I would simply frizbee this
problem board.

My last ditch effort will be to unsolder all the components in that
area and begin ghostbusting. I did meet Bill Murray once a long time
ago at a party. LOL

Thanks again, Mike



Before you begin unsoldering,run the PCB thru your automatic dishwasher
with Calgonite,and then put in a heated (120-140degF) drying box for a few
days.

--
Jim Yanik
jyanik
at
kua.net

On Thu, 14 Jul 2005 12:16:56 -0000
lid (Baytekk) wrote:

My last ditch effort will be to unsolder all the components in that
area and begin ghostbusting. I did meet Bill Murray once a long time
ago at a party. LOL

Don't make this harder than it really is. I wash such boards in a
glass pan with water, then alcohol, then dry in a warm place. This
works as long as there are no parts which the water can seep in and
cause corrosion problems.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Mr Yanik,
I'm new here but I've had the opportunity to read a few of your very
informative posts.

I have a dishwasher, per say, (god, I hope she doesn't read this) so I
had to modify your technique using a 409 soaking followed by a
scauldingly hot water bath in R/O water followed by anhydrous
isopropyl alcohol (for dehydration) followed by a hair drier and then
a few hours to sit, low and behold I achieved the desired result.
I must say I'm astounded that the phantom resistors have been
excorcised completely. Hats off to you Mr. Yanick! Many thanks to
Andreas too!

There was a faint smell of what smelled like bleach as I was giving
the board the hot water bath, the smell of chlorine being released
from a compound perhaps? Or more likely being released from being
trapped. I don't think it was a neutralization process because I
wouldn't have smelled anything. Anyways, the process works.
Thanks, Mike

Well Mike,
looks you have got it. Looks like chlorine components. As I can see Jim
Yanik has given the information too.
May be in your case simply rinsing and brushing with warm (100 F) clear
water would help. But I recommend you use calgonite (Jims proposal) or
at least boil the water half an hour (minimum) to get rid of the
chlorine -- as far as I can remember my holidays in Amerika, all
drinkwater is heavily desinfected with chlorine. If you have a local
highschool, just contact the chmeistry teachers. They should have/be
able to advise too.

Don't worry about the dishwater and your spouse. simply give her your
creditcard and send her for shopping. This will take her an houer, and
that's enough time for the rinse of the boards.

nice collection you have started. May be you are interested to look at
the vitual Tektronix museums, par ex. :

www.amplifier.cd (my NOS 7104 and 7904A are pictured , smile)
http://www.helo.de/helo/museum/museum.htm
http://www.tekscope-museum.de

just to name a few.

I personaly prefer use the 2215/2235. Lightweight, reliable, robust.
And if I need more bandwith, a couple 2465/A/B are all handy. After 25
years of scope collection, my wife doesn't groan when I use the
dishwasher ;-))

ciao,
Andreas

Give her the credit card? I'd rather have her read the dishwasher
wisecrack. LOL... Uh oh, now I'm in real trouble. I just can't win.
LOL

You're right about our H2O here, its chlorinated something fierce.
Think'n ahead, I used charcoal treated reverse osmosis "R/O" water for
the board bath (no chlorine content) and it tastes great too.
I'm gonna peek into Calgonite to see what compounds they use.

I had an opportunity to view the museums you linked to, very nice
indeed. What a great time it was when most everything was built to
last, and the craftsmanship was exquisite.
Thanks again, Mike