Author Topic: Repair and experiments thread: HP 3458A U2  (Read 51894 times)

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Offline TiNTopic starter

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Re: Repair and experiments thread: HP 3458A U2
« Reply #125 on: February 02, 2017, 12:47:57 pm »
Than maybe your fans are just dried out / bad. Replace with new same spec/size Papst/Delta and off you go. I can't hear the unit if I just go another room and close a door :)
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Online Dr. Frank

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Re: Repair and experiments thread: HP 3458A U2
« Reply #126 on: February 02, 2017, 01:07:50 pm »

Dr. Frank
40K resistor from dead A1 is Vishay 301031 hermetical



40K on my 3458A's A1 is Vishay VHP101 (photos posted above). I think same is in my second unit, as it's 5 years younger.

Hi TiN,

so that's the  original resistor (i.e. technology from 1988) which you tested.
It has 1.4ppm/K only, as specified for the 3458A.
Again, I assume C- or K- foil technology inside, by selection fulfilling the tighter spec.

The VHP101 on the other hand, is different, a series combination of a C- and  a K-type resistor element, giving a 5 time better T.C., maybe.

I write "maybe", as this is not reflected in the spec.(which never improved over the version from 1989), and because it's not clear, whether the ~2005 Vishay specification of the VHP101 reflects the same components, as of from 1995 onwards, as used in the 3458As from then on.

I know, that it's a big wish, but maybe it's possible for you, also to measure the T.C. of the 40k, VHP101 resistors, on one of your working A1 boards.
This would give a better baseline about the actual specification also.

Frank
 

Offline TiNTopic starter

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Re: Repair and experiments thread: HP 3458A U2
« Reply #127 on: February 02, 2017, 01:29:48 pm »
Your wish may come true sooner than expected. To celebrate my BD today, I didn't fight my TEA and bought a nice lot of 59 foil resistors off ebay. I mean at 1.65$/piece it's a steal.  :-DMM



Hermeticals are rumored to come from Datron 4950  ;D. One of which is 40K, so in few weeks I hope to receive these and test for TCR. If it's actually much below 0.3ppm, I'll replace original 40K VHP101 to try  ^-^
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Offline mimmus78

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Re: Repair and experiments thread: HP 3458A U2
« Reply #128 on: February 02, 2017, 03:58:16 pm »
Ohh I've seen those resistors on eBay, than I thought it was better to leave to you. :-)
 

Offline mimmus78

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Re: Repair and experiments thread: HP 3458A U2
« Reply #129 on: February 02, 2017, 04:04:23 pm »


New A3 too :). However I'd strongly suggest against replacing fan, it's airflow speed and force are important and I'd keep them as designed.

I'd like start something easy ... getting a fan with similar specs. Only less noiser.



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Online lowimpedance

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Re: Repair and experiments thread: HP 3458A U2
« Reply #130 on: February 02, 2017, 11:16:49 pm »
 Neat little collection of precision goodness there  :). So those hermetic resistors come 'supposedly' from a 4950 !. Or they were going to be used in one as the leads look to be never been soldered.
The 40k and the other one with shorter leads still maybe have not been used either.  :-//
Also noted the values of the other hermetic's is a secret  :D
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline mimmus78

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Re: Repair and experiments thread: HP 3458A U2
« Reply #131 on: February 10, 2017, 09:55:41 pm »
So despite what TiN think I replaced fan of my 3458a with the:

HA60251V4-1000U-A99

on paper this fan should be 13.8 CFM (0,391m³/min) and 10dBa of noise while the original part is rated at 12 CFM at whopping 26dBa (considering the fan is running at 15V I gues it will be more the 30dBa).

This unit can accept up to 13.8V but the 3458a original fan is powered by 15 V, so the idea was to run it with a couple of diode dropper to lower voltage from 15 to 14 V (the plan was also to have a little more CFM to compensate this little voltage drop).

At 14V the fan is very silent, I barely can notice the 3458a when was powered on. Unfortunately 3458a measured +17°C over the ambient temperature so this was to much difference from original fan.
So I decided to give it a push at 15V by removing the diodes and now I have 14°C over the ambient temperature that is slightly better of what I had with the original fan (14.5°C to 15°C).
Air flow and noise was increased (I guess if at 12V is 10 dBa now is around 20 dBa) but it's still acceptable and "down to the noise". Now the question is how much will the fan last with this overvoltage ...

Most probably the next time I will try to use the:

MF60251V2-1000U-A99

this has 19 CFM, still more silent than the original and same power rating than the original fan.
With this fan you will have enough margin for lowering voltage to the rated value and still keep decent air flow and noise.
« Last Edit: February 10, 2017, 10:16:03 pm by mimmus78 »
 

Offline TheSteve

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Re: Repair and experiments thread: HP 3458A U2
« Reply #132 on: February 10, 2017, 10:32:02 pm »
For reference the fan Keysight currently sells for the 3458A is the Papst 622L - easy to get at Digikey/Mouser etc and it will assure proper air flow and is rated to handle 15 volts.
« Last Edit: February 10, 2017, 10:34:45 pm by TheSteve »
VE7FM
 

Offline TiNTopic starter

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Re: Repair and experiments thread: HP 3458A U2
« Reply #133 on: February 13, 2017, 04:33:30 am »
Resistors arrived, time to get that Keithley 7168 nanovolt scanner card busy :)
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Offline View[+]Finder

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Re: Repair and experiments thread: HP 3458A U2
« Reply #134 on: January 21, 2021, 06:49:49 pm »
Is there a better place to discuss repairs to my 3458 option 002 reference? If not, what to do?
 

Offline TiNTopic starter

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Re: Repair and experiments thread: HP 3458A U2
« Reply #135 on: January 21, 2021, 11:15:13 pm »
Just make own thread, like "Standalone 3458A A9 operation" or "troubleshooting A9 module".
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