Specan H-P 141T/8552B/8553B problem

[VK6OX]

Yesterday I was re-acquainted with an old friend...H-P 141T specan with 8552B IF unit and 8553B (0-110MHz) RF unit. I used to operate this gear many many moons ago in my old OTC days, so was looking fwd to putting it to good use in the shack.

I decided to follow the manuals and do an initial calibration connecting the 30MHz cal O/P from the IF unit to the 8553B. Unfortunately, all I see on the trace is the marker (at 40MHz, as expected) but no signal. I decided to switch the "LOG" switch to "Linear" on the IF unit and can JUST discern pips at 30, 60 and 90MHz...these pips should be MUCH larger in amplitude, even in Log mode.

Does anyone know what my problem may be? I'm suspecting balanced mixer diode failure due to I/P overload but have not done further troubleshooting yet.
Is it something simpler i.e. is my "old fart syndrome" getting the better of me?

BTW, I have other RF plugins as well...swapped the 8553B with a 8554L (1250MHz) unit with the same result. (Haven't tried the 8555A yet).

Any help muchly appreciated!

[VK2XAX]

Hi Andy,

I don't know the answer to your question but I do know that ex HP/Agilent engineers inhabit this group here...

http://tech.groups.yahoo.com/group/hp_a ... equipment/

and much help on many things can be gained by posting questions there and visiting the files section.

I have an old Hp8660, a HP5316B and a HP 8901B and have gained insights into keeping them operational with questions to the group.

regards

Tim

[VK4CDI]

Hi Andy,
Off topic, but where in OTC? Ex Moree here.....

Phil VK4CDI

[VK6OX]

Hi Andy,

I don't know the answer to your question but I do know that ex HP/Agilent engineers inhabit this group here...

http://tech.groups.yahoo.com/group/hp_a ... equipment/

and much help on many things can be gained by posting questions there and visiting the files section.

I have an old Hp8660, a HP5316B and a HP 8901B and have gained insights into keeping them operational with questions to the group.

regards

Tim

Thanks for that Tim, I'll go over there and post my query.

Cheers

[VK6OX]

Hi Andy,
Off topic, but where in OTC? Ex Moree here.....

Phil VK4CDI

Hi Phil, Paddo/Broadway in late 60s/mid 70s (Eng. Branch), then to Carnarvon where I stayed until closure in mid 80s, finally to Perth.

[VK4CDI]

RR Andy, Moree 73-80, spent 6 mths at Paddo first, training.....

Cheers
Phil VK4CDI

[VK3AXH]

Hi Andy,

Have you spoken to Alan VK3XPD who has quite a lot of experience with the HP141T series. At present he is in Norfolk but would suggest if you
don''t get an early answer try him in a couple of weeks time. i've not seen that problem with my unit.

Good luck, Ian Vk3AXH

[VK6OX]

Hi Ian,

Tnx for the heads-up re Alan VK3XPD. I'll keep in mind if I don't don't get anything from the Yahoo group.

Cheers

[ZL1UJG]

Hi,
If I remember correctly from 25+ years ago, there should be a couple of bulbs on the front panel, which turn on/off when switching from linear to log or vice versa. (Either one is on) Might have a log/ lin logo next to them.
Anyway I think they might be part of the circuit and affect operation from memory...
Kevin

[VK3ZIE]

Andy, You grew up on them, too. I had the job of populating two successive calibration/development labs back in the late 1960s and early 1970s, and chose the same setup from HP. I now have two complete 141T/8552B/8553B in the shack, and one of them is in the same boat as yours, only it is almost exactly 30db down in sensitivity displaying the marker, and my HP sig gen.
I've checked both double balanced diode mixers, and they appear to be OK. I'm now considering the input capacitor, or the input balanced transformer for the first mixer.
My number two unit works fully up to spec, so at least I have a check on what they should do - it took me quite a while to get "up to speed" again on the old faithful.
Also have another frame with IF and the 8554B, and of course, it has lower sensitivity than it should have, but only about 15db down.
Alan #XPD is only about 5 km down the road from me, so is likely to get a visit from me soon on this subject.
73s, Don. VK3ZIE

[VK6OX]

Andy, You grew up on them, too. I had the job of populating two successive calibration/development labs back in the late 1960s and early 1970s, and chose the same setup from HP. I now have two complete 141T/8552B/8553B in the shack, and one of them is in the same boat as yours, only it is almost exactly 30db down in sensitivity displaying the marker, and my HP sig gen.
I've checked both double balanced diode mixers, and they appear to be OK. I'm now considering the input capacitor, or the input balanced transformer for the first mixer.
My number two unit works fully up to spec, so at least I have a check on what they should do - it took me quite a while to get "up to speed" again on the old faithful.
Also have another frame with IF and the 8554B, and of course, it has lower sensitivity than it should have, but only about 15db down.
Alan #XPD is only about 5 km down the road from me, so is likely to get a visit from me soon on this subject.
73s, Don. VK3ZIE

Hi Don,
Did you ever get your fault resolved? I'd completely forgotten abt this thread until I happened upon it today while looking for something else !
At this point, I still haven't determined the fault with mine...need to get cracking methinks!

73 Andy

[VK3ZIE]

Andy, It appears that there is one coax connection in the inter-unit shell connector which doesn't make contact unless you are VERY careful in aligning the two plug-ins before offering them up to the main-frame.
It is also quite common to find that a previous user did NOT carefully align the two plug-ins before pushing them together, and, in the process, bent either or both of the mountings of either/both of those connectors so that they don't fully engage, and the coax pin/receptacle is one of the last to engage.