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Tek 492 SA PSU removaal

 

Hello again

Have a working Tek SA 492, SN?B05 1984 , 2500 hrs.

to check power supply for RIFA caps, lytic and tants, the. PSU remove procedure in manual is vague on the location of connectors before you pull it.
Any tips or diagrams ? caps to replace or change ?
Your thoughts and advice appreciated?
Many thanks
Jon
 

I've replaced the RIFAs and the cooling fan in my 492AP.

You are right; the manual is not good in this respect. That reflects the, um, "ingenuity" the designers used to fit all the connectors and parts into the available space.

Basically it is a right royal pain in the backside, but I managed it. Having a front cover enables the 492 to be positioned vertically on the bench, which is a major advantage.

The passage of time has mercifully erased many of the details from my mind, but there's weirdly positioned small multipole connector on the side that is "just" pushed back a short distance (?into the carcase?) to release it. When you get a bit further in and are trying to split several subassemblies apart (?a30 from a30a57?), it is easy to remove irrelevant screws.

So my best advice is rather thin: use the manual as a guide, proceed slowly and carefully looking at the problem from all sides (literally!) several times. Then jiggle things. Rinse and repeat. Not for the fainthearted!

ke5fx has created a pdf containing his "Tektronix 49x/275x/279x-Series Spectrum Analyzer Service Notes"


On Sat, 25 Jan 2025 at 23:27, Froggie the Gremlin via <jonpaul=[email protected]> wrote:
Hello again

?Have a working Tek SA 492, SN?B05? 1984 ,? ?2500 hrs.

to check power supply for RIFA caps,? lytic and tants, the.? PSU? remove procedure in manual is vague on the location of connectors before you pull it.
Any tips or diagrams ?? caps to replace or change ?
Your thoughts and advice appreciated?
 

Tom, many thanks for the info.

This analyzer is like a Chinese puzzle, 53 assemblies, huge 2 volume service manual.

Have read KE5FX, fine site.

Analyzer PS voltages , ripple are well in spec, working fine.
On 120V line, VDE caps unlikely to fail.

I will pass on the PS rework for now...

"If it ain't broke, don't fix it".

Jon
 

Change the Rifas as they WILL blow.

? I've worked on a few of these PSU's and they are very reliable, however many/most are 40+ years old now and need some TLC.

?Do you have BOTH manuals??
If not I'll post the 2nd one (with the PSU details) into the archives.

?Good luck?
?
James
 

James thanks for your RIFA warning

They tend to fail on 240v mains, we are 120v here.

This 492 was unused for 20 years and in great shape

Thus I leave it for now as it's working fine, but should rework the PS sometime

Looking for a front cover and printed service manual as I am very bad with PDFs

Have an absolutely fantastic day


Jon
 

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Back in the day...? While I was working at Tek UK (Maidenhead.)

The first 492 that came into the UK was unpacked by Sales for a demo, and instantly blown up!

Those early units were 115V input only...? While the UK was 240V mains!

So (no pressure of course) with no manual, figured out how to get inside, remove the PSU, stripped it down, found the dead parts, and traced the input circuit, converted it from full wave doubler, to full wave rectifier (one trace cut, from memory.)

Replaced the Diodes, Fuse, and power FET'setc in the primary switching side, and gently wound it up on a Variac.? Some strange noises (no load) but no fire or brimstone either.? Checked some secondary voltages, that seemed to be "safe", so powered down, and re-assembled it all.

It powered up fine* and worked without issues.

(*No such thing as PAT testing then, if the ELCB(RCD) on the bench didn't trip, it was good to go!)

Shortly after, it was in the back of a car on it's way to a major UK customer for demo/evaluation, who eventually bought several of them...

(A "Portable" microwave SA?? Only if you were built like Arnie, and even then you'd end up with one arm longer than the other!?? Good instruments for what they were capable of in a "portable" form factor back then.)

Did I get any kudos for that "emergency repair"??? Of course not.?? The first of many such events working for a string US based companies in the UK, when I bailed out sales or similar...? I never learnt!

The 492P appeared a few days before before I left.

I still sometimes come across a 492 (as well as other Tek kit of that era, I was there for 3 years) still sporting stickers, showing my initials...? Never gets me any discount though!

73.

Dave. "DJB"

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