agilent 6632B fault, repair, and several design flaws

[free_electron]

https://keysightsales--c.na158.content.force.com/sfc/dist/version/download/?oid=00D1a000000awb5&ids=0685a00000OMF6P&d=%2Fa%2F5a000001ASPr%2FFgX0i9BUoq0SeRQP0iAWvNDWyAgyHY5n41sMqi9FcUQ&asPdf=true

https://support.keysight.com/s/service-notes?language=en_US
and search for 6632B  it's service note 6632b-03a

text :

"C-13 on the A-3 Bd.has been stressed during the manufacturing process, which causes the
capacitor to short. The shorted cap. pulls down the +5 Volt Bias Supply, thus disabling the
supply from operating.
Solution / Action:
Replace A-3 Front Panel Display Bd. p/n 5063-3432, or if you are equipped to do SMT
repairs, replace C-13, 0.1uf ceramic p/n 0160-7798 "

same misery exists on
6631B-02A 0000A00000 / US37470151
6632B-03A 0000A00000 / US37473858
6633B-03A 0000A00000 / US37470949
6634B-03A 0000A00000 / US37470855
66332A-03A 0000A00000 / US37471398

as they all use the same display board.

i've repaired two with that exact problem and preventively replaced 3 more ( at one point i had 5 of these )
i've had one that failed spectacularly around the big current sense resistor (R473) on the main board. the damn thing burned itself straight through the board at power-on.

the processor board is the same as used in the communication power supplies like 66309d 66311b/ 6613c but with different firmware. and you need to move the flat-flex connector

[free_electron]

anytime you get a HPAK (HP/Agilent/Keysight) machine on the bench : check the service notes

https://support.keysight.com/s/service-notes?language=en_US

[free_electron]

i was re-reading this topic. you used SibaTit . you know where that name comes from ?
SIemens  BArium TItanate capacitor.

They are nothing but class II capacitors which we commonly call X7R , Y5V (and others)
all the ceramic SMD's (class II of course, class i uses a different material ) we buy these days are barium titanate.
They are strange beasts...
- they age :an x7r  can lose up to 5% after 10000 hours, a y5v up to 20%. just by sitting there, doing nothing. When you solder them this effect "resets" . Loss is greatest in the first 10 hours after "reset" (it's logaritmic). so dont use them in opamp filters , or timing applications.
- they are voltage dependent
- they exhibit microphony (barium titanate is a piezoelectric material) . you can make them "sing" , but they can also pick up audio. NEVER use them in frequency loops or opamp feedback circuits in systems subject to large vibrations. They will pick up vibration and create a signal !

the ones you used are the early models ( basically a tube that was squashed down). the later versions are much smaller and basically a 1206 with two legs and overmolded.
Philips(bc components/vishay) produces an orange variant of that.

[Dr. Frank]

i was re-reading this topic. you used SibaTit . you know where that name comes from ?
SIemens  BArium TItanate capacitor.

They are nothing but class II capacitors which we commonly call X7R , Y5V (and others)
all the ceramic SMD's (class II of course, class i uses a different material ) we buy these days are barium titanate.
They are strange beasts...
- they age :an x7r  can lose up to 5% after 10000 hours, a y5v up to 20%. just by sitting there, doing nothing. When you solder them this effect "resets" . Loss is greatest in the first 10 hours after "reset" (it's logaritmic). so dont use them in opamp filters , or timing applications.
- they are voltage dependent
- they exhibit microphony (barium titanate is a piezoelectric material) . you can make them "sing" , but they can also pick up audio. NEVER use them in frequency loops or opamp feedback circuits in systems subject to large vibrations. They will pick up vibration and create a signal !

the ones you used are the early models ( basically a tube that was squashed down). the later versions are much smaller and basically a 1206 with two legs and overmolded.
Philips(bc components/vishay) produces an orange variant of that.

Hello free_electron,

yes I know, I simply  had them lying around since the 1980ties, I think.
I bought these to assemble a 128kB memory extension card for my APPLE ][e clone 
These were ceramic capacitors with higher ESR, I guess, to supress the glitches from the DRAM chips (don't remember correctly anymore).
I just mentioned this strange name SiBaTit so nobody wondered about these blue capacitors.

This problem with high C-V ceramic capacitors is really a pain. As Ta capacitors are not allowed/wanted any more, our engineers use e.g. 22µF/6.3V X7R or X7S capacitors behind a 5V LOD regulator, and some brands, even for these Automotive grade ceramics, show an excessive capacitance drop to 30%, or below, with DC bias  , over time and over temperature, so that the LOD soon starts oscillation. I really mean, that this 22µF might drop to < 6µF!
This effect was, or is not so prominent with lower CxV capacitors, like these 100nF blocking caps, and with reasonable compliance voltage, i.e. operating voltage well below nominal / max voltage rating.

Singing ceramic capacitors are quite rare, we have more problems with singing coils, sitting in SMPSUs.
Root cause is a subharmonic due to loose coil windings.

Frank   

[Dr. Frank]

"C-13 on the A-3 Bd.has been stressed during the manufacturing process, which causes the
capacitor to short. The shorted cap. pulls down the +5 Volt Bias Supply, thus disabling the
supply from operating.
Solution / Action:
Replace A-3 Front Panel Display Bd. p/n 5063-3432, or if you are equipped to do SMT
repairs, replace C-13, 0.1uf ceramic p/n 0160-7798 "

Many thanks for this heads-up, I only have seen and downloaded SN -08 and -09.

Following the description, it was a manufacturing damage, i.e. they cracked this big 1206 because the pick and place nozzle was incorrectly programmed in height.
Or it was cracked by bending the whole PCB after reflow.
We've blocked such big case sizes, also because of this latter problem.

I don't see a hint, that a wrong nominal voltage was used.

Anyhow, I will also look for the schematics from these other devices..

Frank

[Pete2]

Thanks for the information all, didn't know about the service notes. I will soon have a 66332A for repairs. Apparently it's a no power unit, maybe even the mentioned blank display type.

I noticed another service note for the unit: 66332A-10 that requires a diode to be added on the board. The note is dated 2011 so I would have to add that too? Seems like its a BAS45 according to a cross ref. table for HP parts (1901-1344).