Hello,

a dude named CarlsonLabs has had a 2h video on replacing these neons. Never sat through it all the way to the fartingsound, don?t have a link handy but wanted to mention it. If there is interest I can go hunt it down.


Tam

With best regards
Tam HANNA

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On 2020. 04. 07. 16:41, n4buq wrote:

Same problem with neon-choppers as found in the 410C.? HP replaced that with a fully solid-state board towards the end of production.? I wonder if something similar could be done for the 334A?

Thanks,
Barry - N4BUQ

----- Original Message -----

From: "Chuck Harris" <cfharris@...>
To: [email protected]
Sent: Tuesday, April 7, 2020 8:52:18 AM
Subject: Re: [HP-Agilent-Keysight-equipment] Anyone out there fix a partially working 334A I need desperately to get
it up and running!

The killer problem I have found with 334A's, is they have an optically
driven chopper that relies on NE2 style neon bulbs, and CdS photo resistors
to do the chopping.

The problem is two fold:? First, the neons get smoky inside, and don't put
out enough light to switch the photo resistors, and second, the CdS photo
resistors sometimes fail.

The neons used have a little radioactive material sintered into their
electrodes,
to make them dark fire reliably, and modern replacements don't.? And, the
CdS photo resistors were selected and matched for maximum on/off resistance
spread.? CdS photo resistors run afoul of the RoHS regulations because of the
Cadmium, and are very expensive, if you can get them at all. It is unlikely
you can find the super wide spread selected variety that HP used.

All of the other problems I have seen have been simple capacitor replacement
issues.? The 334A is stocked full of TE/30D style electrolytic capacitors,
and
their rubber seals have pretty much all turned to stone by now.

Replacing the capacitors won't have any real effect on calibration.

-Chuck Harris

Steve wrote:

I have an Hp 334A that powers on and appears to function partially but I’m
not sure what all could be wrong with it. If anyone fixes these units at a
reasonable price I would be interested in having it put back in top notch
shape with a good calibration. I restore vintage hifi and I need to get it
up and going as quickly as possible.

On 4/7/20 12:04 PM, Jeremy Nichols wrote:

Purely out of curiosity, what is the purpose of a chopper in a 334
distortion analyzer? HP used choppers in a lot of their DC voltmeters to
convert the DC to AC. They’d run the AC through some amplifiers and then
convert back to DC to run the meter. That took care of the old DC
amplifier drift problems. Since a distortion analyzer is already working
with AC, I would think a chopper wouldn’t be necessary. Obviously
there’s something I’m missing.?

Unless my memory is failing, it's not strictly a chopper, but it's
part of the automatic tuning system. The choppers are
digitally-controlled switches, but I believe the LDR-based subsystem in
the 33x distortion analyzers are more "analog" in nature, to follow the
fundamental frequency automatically.

-Dave

Thanks Nigel,
I have found the IFR group. I should have looked first. ?
Thanks
Dave

On Apr 7, 2020, at 2:50 AM, nigel adams via groups.io
<nigel.adams@...> wrote:

? Have you tried the IFR group as well - there are people who have
this stuff and might be able to help.
------------------------------------------------------------------------
*From:* [email protected]
<[email protected]> on behalf of Dave Miller
<ve7hr@...>
*Sent:* 07 April 2020 03:55:29
*To:* [email protected]
<[email protected]>
*Subject:* [HP-Agilent-Keysight-equipment] Hints on removing burned
tantalum residue
?
Not directly HP related but this is where the knowledge is.
I am starting to repair an IFR-1200S that had an incident.
<IMG_0884.jpeg>
<IMG_0886.jpeg>


A 150 uF 15V tantalum went up in smoke.
What is the best solvent to remove the residue on the rest of the PCB.
Isopropyl does not take all of it off? Want to get it all clean before
I replace parts and continue the repair.
Thanks
Dave?

hello Dave,

yes, specials:
The Power Line Supply is a Option and not always inside.
427A have a Set of 4 obsolete 6.75V mercury batterys,
if they are tired and there is no PSU, build it self.

The instrument needs ±13,5V.
Another way is to use 2 pcs. of 9V Blocks, it will work with them also.

Martin

Am 07.04.2020 um 06:17 schrieb Dave McGuire:

On 4/7/20 12:14 AM, Paul Bicknell wrote:

Just switched on a 427A volt meter that I rescues a few weeks ago

Just wondering is their any think special about it and is it worth spending
any time on as it reads low

?? I've never put my hands on one, but I checked out the specs a bit.? It
doesn't seem particularly noteworthy in any specific way, but it sure
does look like a nice handy all-around bench meter with a nice big meter
face.

????????????? -Dave

On 4/7/20 12:14 AM, Paul Bicknell wrote:

Just switched on a 427A volt meter that I rescues a few weeks ago

Just wondering is their any think special about it and is it worth spending
any time on as it reads low

I've never put my hands on one, but I checked out the specs a bit. It
doesn't seem particularly noteworthy in any specific way, but it sure
does look like a nice handy all-around bench meter with a nice big meter
face.

-Dave

Same problem with neon-choppers as found in the 410C. HP replaced that with a fully solid-state board towards the end of production. I wonder if something similar could be done for the 334A?

Thanks,
Barry - N4BUQ

----- Original Message -----

From: "Chuck Harris" <cfharris@...>
To: [email protected]
Sent: Tuesday, April 7, 2020 8:52:18 AM
Subject: Re: [HP-Agilent-Keysight-equipment] Anyone out there fix a partially working 334A I need desperately to get
it up and running!

The killer problem I have found with 334A's, is they have an optically
driven chopper that relies on NE2 style neon bulbs, and CdS photo resistors
to do the chopping.

The problem is two fold: First, the neons get smoky inside, and don't put
out enough light to switch the photo resistors, and second, the CdS photo
resistors sometimes fail.

The neons used have a little radioactive material sintered into their
electrodes,
to make them dark fire reliably, and modern replacements don't. And, the
CdS photo resistors were selected and matched for maximum on/off resistance
spread. CdS photo resistors run afoul of the RoHS regulations because of the
Cadmium, and are very expensive, if you can get them at all. It is unlikely
you can find the super wide spread selected variety that HP used.

All of the other problems I have seen have been simple capacitor replacement
issues. The 334A is stocked full of TE/30D style electrolytic capacitors,
and
their rubber seals have pretty much all turned to stone by now.

Replacing the capacitors won't have any real effect on calibration.

-Chuck Harris

Steve wrote:

I have an Hp 334A that powers on and appears to function partially but I’m
not sure what all could be wrong with it. If anyone fixes these units at a
reasonable price I would be interested in having it put back in top notch
shape with a good calibration. I restore vintage hifi and I need to get it
up and going as quickly as possible.

Same problem with neon-choppers as found in the 410C. HP replaced that with a fully solid-state board towards the end of production. I wonder if something similar could be done for the 334A?

Thanks,
Barry - N4BUQ

----- Original Message -----

From: "Chuck Harris" <cfharris@...>
To: [email protected]
Sent: Tuesday, April 7, 2020 8:52:18 AM
Subject: Re: [HP-Agilent-Keysight-equipment] Anyone out there fix a partially working 334A I need desperately to get
it up and running!

The killer problem I have found with 334A's, is they have an optically
driven chopper that relies on NE2 style neon bulbs, and CdS photo resistors
to do the chopping.

From: "Chuck Harris" <cfharris@...>
To: [email protected]
Sent: Tuesday, April 7, 2020 8:52:18 AM
Subject: Re: [HP-Agilent-Keysight-equipment] Anyone out there fix a partially working 334A I need desperately to get
it up and running!

The killer problem I have found with 334A's, is they have an optically
driven chopper that relies on NE2 style neon bulbs, and CdS photo resistors
to do the chopping.

The problem is two fold: First, the neons get smoky inside, and don't put
out enough light to switch the photo resistors, and second, the CdS photo
resistors sometimes fail.

The neons used have a little radioactive material sintered into their
electrodes,
to make them dark fire reliably, and modern replacements don't. And, the
CdS photo resistors were selected and matched for maximum on/off resistance
spread. CdS photo resistors run afoul of the RoHS regulations because of the
Cadmium, and are very expensive, if you can get them at all. It is unlikely
you can find the super wide spread selected variety that HP used.

All of the other problems I have seen have been simple capacitor replacement
issues. The 334A is stocked full of TE/30D style electrolytic capacitors,
and
their rubber seals have pretty much all turned to stone by now.

Replacing the capacitors won't have any real effect on calibration.

-Chuck Harris

Steve wrote:

I have an Hp 334A that powers on and appears to function partially but I’m
not sure what all could be wrong with it. If anyone fixes these units at a
reasonable price I would be interested in having it put back in top notch
shape with a good calibration. I restore vintage hifi and I need to get it
up and going as quickly as possible.

On Apr 7, 2020, at 2:41 AM, Jan Weber via groups.io <jancarlweber@...> wrote:

?

May I suggest using a glass fiber pen/brush for removing burnt-in particulate matter and charring?

I've used them in the past to clean corrosions caused by leaking batteries.?

Regards

Jan

Ed Breya via <edbreya=[email protected]> schrieb am Di., 7. Apr. 2020, 10:35:

What a mess - it really did a number on that board section. I agree that acetone would be a pretty good solvent for some of the char, but unfortunately, it may not clean it all off. Some is likely carbon particles (from burning up the coating) and Ta oxides (from the cap guts) splattered onto (and into) the surfaces, and no conventional solvent will dissolve it. The good news is that even if you can't get it spic and span, any remaining residue probably won't hurt the circuit operation after cleaning and repair.

Besides some solvent action, good mechanical scrubbing should help. I'm not sure if your comment about IPA is a question (will it work?) or a statement (tried and it doesn't work). I'd start with IPA, if you haven't already. Paint thinner or acetone are logical next steps. Acetone may be a little too intense to leave on for very long.

Presuming you don't want to remove the board from the RF assembly, which appears to have its feed-throughs soldered to the board, the trick is to be able to work on board cleanup without getting anything bad into the RF. IPA and acetone would probably be best then, since they're miscible with water and will evaporate quickly, while paint thinner would be a bit messy and slow to depart.

If the board can be readily removed, you have more options such as aqueous washing with detergents, and some gentle abrasive action such as an opaque toothpaste worked with - of course - an old toothbrush, to scrape off the particles that aren't too tightly embedded in the surfaces. Regardless of the solvents and methods, I always use old toothbrushes for scrubbing. Higher intensity solvents may dissolve or degrade the bristles and heads, so you have to work fast in some cases.

Another option, if you have access to the appropriate equipment, is to skip solvents altogether and do purely mechanical cleaning, like with a soda or walnut shell blaster.

Good luck.

Ed

On Apr 7, 2020, at 2:50 AM, nigel adams via groups.io <nigel.adams@...> wrote:

? Have you tried the IFR group as well - there are people who have this stuff and might be able to help.

---

From: [email protected] <[email protected]> on behalf of Dave Miller <ve7hr@...>
Sent: 07 April 2020 03:55:29
To: [email protected] <[email protected]>
Subject: [HP-Agilent-Keysight-equipment] Hints on removing burned tantalum residue

?

Not directly HP related but this is where the knowledge is.
I am starting to repair an IFR-1200S that had an incident.

<IMG_0884.jpeg>

<IMG_0886.jpeg>

A 150 uF 15V tantalum went up in smoke.
What is the best solvent to remove the residue on the rest of the PCB. Isopropyl does not take all of it off? Want to get it all clean before I replace parts and continue the repair.
Thanks
Dave?

I have an Hp 334A that powers on and appears to function partially but I’m not sure what all could be wrong with it. If anyone fixes these units at a reasonable price I would be interested in having it put back in top notch shape with a good calibration. I restore vintage hifi and I need to get it up and going as quickly as possible.

What a mess - it really did a number on that board section. I agree that acetone would be a pretty good solvent for some of the char, but unfortunately, it may not clean it all off. Some is likely carbon particles (from burning up the coating) and Ta oxides (from the cap guts) splattered onto (and into) the surfaces, and no conventional solvent will dissolve it. The good news is that even if you can't get it spic and span, any remaining residue probably won't hurt the circuit operation after cleaning and repair.

Besides some solvent action, good mechanical scrubbing should help. I'm not sure if your comment about IPA is a question (will it work?) or a statement (tried and it doesn't work). I'd start with IPA, if you haven't already. Paint thinner or acetone are logical next steps. Acetone may be a little too intense to leave on for very long.

Presuming you don't want to remove the board from the RF assembly, which appears to have its feed-throughs soldered to the board, the trick is to be able to work on board cleanup without getting anything bad into the RF. IPA and acetone would probably be best then, since they're miscible with water and will evaporate quickly, while paint thinner would be a bit messy and slow to depart.

If the board can be readily removed, you have more options such as aqueous washing with detergents, and some gentle abrasive action such as an opaque toothpaste worked with - of course - an old toothbrush, to scrape off the particles that aren't too tightly embedded in the surfaces. Regardless of the solvents and methods, I always use old toothbrushes for scrubbing. Higher intensity solvents may dissolve or degrade the bristles and heads, so you have to work fast in some cases.

Another option, if you have access to the appropriate equipment, is to skip solvents altogether and do purely mechanical cleaning, like with a soda or walnut shell blaster.

Good luck.

Ed