[Test-Equipment] Need help with the HP 8553-L /141-T

[cemilton at aol.com]

Hello Alan and the group...............



Your commented:




"Hi Chuck may be right about the mixer diodes but it doesnt sound like it.

There are a number of other places to look first before diving into a

difficult (or expensive repair)"



Thanks Alan for the comments.  I just started reading the schematic for the 8553B as I don't 

yet have one for the 8553-L (the one in question).  I believe they are at least close enough

to allow me some initial testing.



If you are seeing the 30MHz cal signal and harmonics it sounds as though the

mixer is working in some fashion. The next thing to look at is the mating

D-connectors between the IF and RF modules I actually had one pin bent

inwards on one of the systems I acquired and got exactly the same symptom

that you describe......not gain...you may find the cal signal is does not

align with the quoted value (engraved on the panel) Make sure that these

connectors mate properly before trying to offer up the two modules to the

frame. They can be misaligned and not seated properly ...without the problen

of a bent pin (I managed to carefully straighten it with it breaking !!)



Yes, I see the calibration "blip" but can't really say there are harmonics there too.  The 

mechanical checks of the D-connectors is a good idea.  I'll give them a look under

the magnifier and clean any oxidation I see.



The next most important thing to do is take the bottom cover off the the

frame use the 141T manual and locate the power supply test pins and adjuster

pots. These will have drifted out. Reset them with a reasonable good (one

you trust) DMM they do need to be set farly accurately and the carbon

resistors have a record of drifing up. If you run out of adjustment you may

need to replace one or more fixed  resistor. Do the adjustment in the right

order as per the book.



The 141-T manual is now downloaded and I'll review your suggested procedures.



Thanks so much for the comments.  I've scoured the archives for this reflector and while 

there are numerous comments on the 141-T, none have approximated the conditions I inquired about.  

As the saying goes, "Keep those cards and letters coming".  I will need more advice as the

repair proceeds.



Thanks Alan and others..............



73 de W4MIL

Chuck