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Repairing blown up terminators on SD-30

Dd Dd
 

I have an SD-30 head for 11800/CSA803 series with destroyed terminator resistors that I am planning to repair.

They are (were) a pair of thin film 100R on each side of the input microstrip, each connected to it with bondwires. Bondwires seem to be intact and sampling diode bridge works fine.

http://leobodnar.com/balloons/NTP/SD-30-blown.jpg
http://leobodnar.com/balloons/NTP/SD-30-input-detail.jpg

I think someone here repaired SD-24 or SD-26 resistors by installing 0402 but SD-30 playfield is much smaller.

I am contemplating either:

1) soldering 2x100R RF 0201s across the gold plated tabs of protruding part of the 2.9mm connector. This will probably screw up a lot of things (reflections, bond wires inductance compensation, etc) but will keep the head useable to about 20GHz (random nice figure)

2) bonding or conductive-epoxying a pair of 01005 resistors near where original resistors where

3) applying small, controlled amount of conductive epoxy across the destroyed terminators

I am not sure why designers decided to connect terminators to the input section with a bond wire. It looks like it was possible to run the resistor film between the input and nearby groundplane directly. Perhaps it was laser-trimmed after assembly... The terminator bondwire is quite large and ugly. Maybe it got compensated by widening the microstrip near the wires.

Leo

 

On 30 Oct 2017 21:08:23 +0000, you wrote:

...

I am not sure why designers decided to connect terminators to the input section with a bond wire. It looks like it was possible to run the resistor film between the input and nearby groundplane directly. Perhaps it was laser-trimmed after assembly... The terminator bondwire is quite large and ugly. Maybe it got compensated by widening the microstrip near the wires.

Leo
Maybe the bond wire was used to deliberately add a controlled amount
of inductance to the termination?

For surface mount RF terminations using standard parts, I have heard
of people mounting the resistors upside down to minimize the
inductance from the surface mount part end terminations which fold
around the ends.

Dd Dd
 

I use reverse-mounted 0201 resistors on my pulser. I would say the effect is marginal at best. You trade lower inductance for higher capacitance because of the poking stubs.

I am prepared to pony up for proper flip-chip RF resistors like these http://www.vishay.com/docs/53014/ch.pdf
They are about $5-$10 each.

Leo
---In TekScopes@..., <davidwhess@...> wrote :

For surface mount RF terminations using standard parts, I have heard of people mounting the resistors upside down to minimize the inductance from the surface mount part end terminations which fold around the ends.

Dd Dd
 

OK, fixed it for now.

You have 10 minutes to mix deadly epoxy, apply it to 1x1mm total working area and place two 02016 RF resistors without shorting the underlying substrate tracks. No pressure at all.

Cheers
Leo

Dd Dd
 

stefan_trethan
 

Will you satisfy my morbid curiosity and tell me which epoxy this is?
It's rare to see such dire warnings outside the state of California!

ST

On Thu, Nov 2, 2017 at 4:34 PM, groups1234567890@... [TekScopes]
<TekScopes@...> wrote:
Here are some photos from repair session:

http://leobodnar.com/balloons/NTP/SD-30-repair1.jpg
http://leobodnar.com/balloons/NTP/SD-30-repair2.jpg
http://leobodnar.com/balloons/NTP/SD-30-repair3.jpg
http://leobodnar.com/balloons/NTP/SD-30-repair4.jpg
http://leobodnar.com/balloons/NTP/SD-30-repair5.jpg

Cheers
Leo

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Posted by: groups1234567890@...
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Nice work. Can you divulge the epoxy details?

Regards

----- Original Message -----
From: groups1234567890@... [TekScopes]
To: TekScopes@...
Sent: Thursday, November 02, 2017 11:29 AM
Subject: [TekScopes] Re: Repairing blown up terminators on SD-30



OK, fixed it for now.

You have 10 minutes to mix deadly epoxy, apply it to 1x1mm total working area and place two 02016 RF resistors without shorting the underlying substrate tracks. No pressure at all.

Cheers
Leo



[Non-text portions of this message have been removed]

Ed Breya
 

Yes, that picture of the warning label is disturbing - it would be very informative to see what type of Ag epoxy this is, and its MSDS.

Ed

Dd Dd