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EIP 545B Frenquency counter

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HighPrecision:

--- Quote from: douardda on January 22, 2018, 11:31:07 pm ---when locked on a (strong enough) signal on band 3, the IF sits at roughly 127.9MHz instead of 125MHz as described in the manual, for which the troubleshooting tree concludes that "VCO or LOCK CIRCUITRY on A108 BAD".

--- End quote ---
127 MHz is correct, EIP has changed IF frequency in later A203 revisions, all 'B' models are 127 MHz.

You can look at the A203 internal IF amplifier, if I remember correctly at right side looking from front, sometimes I've found some leaking SMD ceramic capacitors. Please DO NOT touch the small wires coming from YIG filter through a hole, these are folded as a kind of inductance during factory calibration.

Check also if the screws holding the YIG filter to A203 box are tighten, sometimes loss of performance happen for these loose screws.

douardda:

--- Quote from: HighPrecision on January 23, 2018, 10:17:04 am ---127 MHz is correct, EIP has changed IF frequency in later A203 revisions, all 'B' models are 127 MHz.

--- End quote ---
Ghezz, thanks you so much.


--- Quote from: HighPrecision on January 23, 2018, 10:17:04 am ---You can look at the A203 internal IF amplifier, if I remember correctly at right side looking from front, sometimes I've found some leaking SMD ceramic capacitors. Please DO NOT touch the small wires coming from YIG filter through a hole, these are folded as a kind of inductance during factory calibration.

--- End quote ---

Ok I'll be extra careful! How leaky are we talking about there? like they begin to behave like a resistor on DC? Is probing with an LCR meter is enough to detect them (like the DER DE-5000 I have)?


--- Quote from: HighPrecision on January 23, 2018, 10:17:04 am ---Check also if the screws holding the YIG filter to A203 box are tighten, sometimes loss of performance happen for these loose screws.

--- End quote ---
I'll give the YIG filter a look too. In fact I've opened the YIG to be able to clean it (enclosure was really rusty, as can been seen on the pictures I posted at the beginning of the thread), so maybe there is some "alignment" that must be taken care of when putting is back together. However, it did have poor sensibility before being taken apart, so...

[mode miracle]Don't you have a copy of the 545B service manual somewhere? It would be so much easier! [/mode miracle]

douardda:
I've opened A201 to make a quick check of capacitors in there, nothing stroke my eye.
But I've also disassembled the YIG filter, and I may have found the reason it works poorly on band 3... and it's probably not a very good news.

I've looked at the YIG spheres (since there are 2 of them in this filter) using my cheap USB microscope.

Top side:


And the bottom side (with copper shim removed):


For which a closer look gives:



on which you may see the problem, more visible on this one:



It's not attached to the "holding rod" any more. Luckily, the cage is small enough for the sphere not to fall, but it not seated at it's correct position either...

Should I try  to stick it back to the holder? With what kind of "glue"? For the record, these 2 balls are very small, maybe 2 or 3/10 mm, so it will not be an easy task...

David
   


 

douardda:
And in the (probable) case I do not succeed in fixing this YIG filter, any idea what is the "meaning" of the '-09 REVA' on my unit (part number is 2010241-09 REVA)?

There are a few of the on eb, but none have exactly the same part number. For example there is a reasonably cheap 2010241-08 Rev. D available, is there a chance it will work (after recalibration)?
 
David

HighPrecision:

--- Quote from: douardda on January 23, 2018, 10:17:43 pm ---There are a few of the on eb, but none have exactly the same part number. For example there is a reasonably cheap 2010241-08 Rev. D available, is there a chance it will work (after recalibration)?

--- End quote ---
"-08" is for 5x8B (26.5 GHz) models, odd numbers are for 20GHz ones, 'B' models start with "-05" (127MHz IF), my informations are too old, I suppose that the "-07" is also for 'B' 20GHz... no idea for Special WB-68 of your unit.


--- Quote from: douardda on January 23, 2018, 10:01:03 pm ---Should I try  to stick it back to the holder? With what kind of "glue"? For the record, these 2 balls are very small, maybe 2 or 3/10 mm, so it will not be an easy task...

--- End quote ---
Sorry, I haven't tried any repair at this level, normally the entire A203 converter has to be returned to factory for exchange, in few cases I have repaired the manageable areas, only in one case I have success in repair the MW fllter for a short of COMB drive signal to ground, purely a mechanical issue :)

If you have the possibility to measure the input RL (VSWR) setting the YIG coil current for a specific tune frequency, you can determine if the coupling between input RF link (that is critical) and the YIG sphere is compromised or not.


--- Quote from: douardda on January 23, 2018, 09:21:35 pm ---Ok I'll be extra careful! How leaky are we talking about there? like they begin to behave like a resistor on DC?

--- End quote ---
Yes, DC leak that affect BIAS of amplifiers stages.


--- Quote ---[mode miracle]Don't you have a copy of the 545B service manual somewhere? It would be so much easier! [/mode miracle]

--- End quote ---
I have some in paper form, unfortunately NOT in pdf, another member has already asked me for a manual, at the moment don't have much time to do long and tedious scanning sessions...

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