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g4uui_op 11th Dec 2011 10:15 am

Spectrum Analyser TR4172
Hello all,

I wonder if anyone out there knows what the amplifier in the interface unit is, as I have no information on this device. This is the only info that does not appear in the manuals. My unit is now approx 20-30dB deaf and I would like to bring it back to a fully working unit.

stuartp 12th Feb 2012 1:02 am

Re: Spectrum Analyser TR4172

I also have a sick TR4172 in my case the RF section seems to be completely useless?

However, I got the unit without the main interconnecting lead between the two units and have used a standard one to one connection lead. Could someone confirm that is correct or are the plugs wired up differently i.e. the pins from one plug connected two different pins on the other plug?

Stuart Perry

G0HZU_JMR 12th Feb 2012 7:17 pm

Re: Spectrum Analyser TR4172
Hi Stuart
Are you referring to the J2-J2 connector lead or the one called J1 BUS - J1 BUS?

I have one of these analysers and mine has two main connecting leads at the back (plus the IF coax connection of course)


stuartp 22nd Feb 2012 8:58 pm

Re: Spectrum Analyser TR4172
Hi Jeremy
I'm refering to the J1 - J1 lead (I wired this up pin to pin i.e. pin1 to pin1 etc)as I think the J2 -J2 lead is for makers as from memory it has two / three rf connectors and nine pins which I assumed are wired one to one? Any help with the lead configuration settings would be greatly appreciated!

I have connected the IF BNC connectors up.

Many thanks
Stuart Perry

G0HZU_JMR 22nd Feb 2012 10:37 pm

Re: Spectrum Analyser TR4172
3 Attachment(s)
Hi Stuart

I'm pretty sure the J1-J1 connector is wired straight but I'll buzz it out tomorrow.

Here's some quick images of the insides to show how the originals are made.

I'll check out the screening jacket as well to see if it goes to any pins or just the connector shell.


G0HZU_JMR 22nd Feb 2012 10:53 pm

Re: Spectrum Analyser TR4172
I had a quick look inside the J2-J2 connector shells and got a bit of a surprise...

The 5 'data' pins are dummies at both ends!

i.e. there is no connection to these pins at either end. Not even a termination or link etc. Just untouched as new unused pins on the insides at BOTH ends.
Note that my analyser has options 5 and 7 stamped on the back so maybe these 5 data pins on J2 get used for other options?

The RF connections are one to one on J2-J2.

I'll test J1 tomorrow as it's a bit late and also a bit fiddly. Best done in daylight.

G0HZU_JMR 23rd Feb 2012 6:13 pm

Re: Spectrum Analyser TR4172
OK I just buzzed out the J1-J1 bus cable and it is indeed a 1 to 1 cable. I took some time over this and marked up the edge connector every 5 pins to make sure I didn't lose synch between cables.

It buzzes out 1:1 and also the screen shells show good conductivity from end to end and they also have conductive screen plates as per the images above (the long shiny metal plates running the length of the blue body) to ensure a solid screen connection around the outside of the whole assy and the screen of the cable.

The plates mate with the outer body of the connector on the analyser to give a solid screen connection from the screen on the cable to the analyser chassis.

There is no connectivity from the outer screen on the cable to any of the bus pins when the cable is tested in isolation from the analyser.

stuartp 23rd Feb 2012 9:16 pm

Re: Spectrum Analyser TR4172
Thank you guys I guess I must have a sick RF section?

Stuart Perry

G0HZU_JMR 24th Feb 2012 2:17 pm

Re: Spectrum Analyser TR4172
Hi Stuart
I'm not sure if you mean the RF front end is faulty or what is referred to as the RF Block.
The RF Block does the 2nd, 3rd and 4th mixes.

If you ever feel like scrapping it then I'd offer you something for the analyser because I'd ideally like a second unit for spares to support this one.

I've been using this one for over 22 years either at my place of work or more recently here at home and it's been a great analyser and I dread the day it finally develops a major fault that puts it out of service for good...


stuartp 26th Feb 2012 6:12 pm

Re: Spectrum Analyser TR4172
Hi Jeremy
I'll try and spend some more time on it when I can but have a two year old to contend with she has just woken up bye.

Stuart Perry

Brian G8MUE 19th Aug 2012 12:59 pm

Re: Spectrum Analyser TR4172
Hi Folks,
I have a TR4172 which is about 30db deaf ! I have full manuals and suspect that the 1st mixer is zapped. Thats the usual reason for deaf Spectrum Analysers. Anyone know a suitable substitute for the ring of 8 diodes ("D1" which only has a "house code" in the parts list). Because opposite sides of the ring are DC connected, I cannot see an easy way to test it without removing it. GUII OP's post of December 2011 sounds similar - was that problem resolved?
Regards, Brian G8MUE

G0HZU_JMR 20th Aug 2012 8:58 pm

Re: Spectrum Analyser TR4172
1 Attachment(s)
I've not looked at the mixer circuit yet but what I can share is what happened to my TR4172 a while ago. It suddely went deaf on one attenuator setting which meant I couldn't run the inbuilt auto cal routine any more (takes a minute or so to run) to sharpen up the accuracy for critical measurements.

So I was faced with buying a new attenuator or taking it apart to see what was inside.

What I did find was that Advantest had fitted a tiny little soft ferrite? block over the microstrip path to this attenuator and they had glued it there.

Over time the glue attacked the microstrip and one day it finally went open circuit. So the >40dB attenuator settings all died.

Luckily it proved an easy repair.

See the image below. The yellow arrow points to the start of the eroded microstrip areas.

There's no way this happened with RF overload because the signal break is on the 'attenuated' side of the attenuators and the attenuators are intact and there was no sign of thermal damage. Also, the erosion area was perfectly contained under the old glue.

You can see how tiny the attenuators are and why this analyser has max +20dBm drive level. The big black thing under the yellow arrow is the soft ferrite? thing.

It does seem to improve the attenuator accuracy up at >1500MHz so I refitted it with different adhesive once repaired. TBH I don't really know what it is made of of why it is there.

The reason I'm telling you this is because they may have used this ferrite + glue elsewhere. My analyser must be nearly 25years old so this nasty glue has had all this time to react with and eat away the microstrip.

zack003 5th Nov 2012 10:57 am

Re: Spectrum Analyser TR4172
Hello everyone,

I'm another owner of a TR4172 with defective CRT. I don't want to sell it because RF part continue to works well in spite of its 25 years, so I need to repair it. Is there anyone wants to sell the visualization module (upper part)? Here is some pictures of the defective CRT:

G0HZU_JMR 6th Nov 2012 9:10 pm

Re: Spectrum Analyser TR4172
Can't help you with a spare CRT or top unit but are you still able to use it by getting display data onto a PC or other display?

The reason I ask is there is the XYZ (option 3) to allow a remote display.

Also, you can access internal memory via GPIB so you could in theory dump the 1000x1000 point trace data to a PC and get a display on a PC screen if you created suitable SW.

I'd imagine the refresh rate would be quite slow but these are things I am considering with mine as my CRT won't last forever and I don't have option 3 fitted...

In the meantime I have controlled it and dumped 'some' data from mine via GPIB using some simple VB code when I was experimenting with the programming command set and I've also managed to get some screen plots using the freebie KE5FX toolkit via GPIB.

G0HZU_JMR 8th Feb 2015 1:05 am

Re: Spectrum Analyser TR4172
Sorry to drag up an old thread but in recent weeks I've been servicing both of my Advantest TR4172 analysers and I found a minor issue in the dreaded and undocumented mixer/IF interface unit.

So I spent a bit of time reverse engineering it. All my findings are subject to a degree of technical risk but if anyone wants to know about the amplifer in there or how it is biased or how the rest of the interface unit is designed (i.e. what is in there and what it does) then I can post the info up on here. I can do the same for the first mixer unit too.

Both of my analysers were showing a gradual reduction (over time) in front end linearity and a gain loss of a few dB and a slight degradation in DANL.

This analyser has a very beefy first mixer using 8 diodes (+22dBm LO drive level typical) and typically gives a mixer input IP3 of +22dBm.

But my analysers had slowly faded to giving only about +10dBm IP3 and this is down at the performance level of my old HP8568B with its very basic two diode mixer.

If I had not spotted/fixed this slow decline in gain and IP3 then the interface unit would have degraded to a point where the analyser had gone very deaf. i.e. there is an issue in this module caused by corrosion over time.

I can post up all the service/repair info if it is needed. i.e. if G4UUI and G8MUE still have their analysers stashed away as BER.

Brian G8MUE 22nd May 2015 2:41 pm

Re: Spectrum Analyser TR4172
Since my post in Aug 2012, I have continued to use my TR4172 despite the 30db deafness. When I switch on and set the centre to 145MHz and the span to 10MHz, the baseline (the middle of the noise fuzz) is at -83db (displayed). Connecting a signal of -50dbm from my HP8654A to input 1, is just visible in the noise. I have no reason to suspect the HP which also agrees with the 50MHz reference output from the TR4172. The input attenuator operates as it should on all steps. The pre-amp at input 2 works as it should.

Without a spare diode ring for the 1st mixer, I am reluctant to open it up. (A deaf SA is better than no SA). I have recently purchased (about £50 from a well known auction site) a "simple spectrum analyser" from Hong Kong. This USB instrument does seem to be able to make useful measurements of signal amplitude and frequency with an effective bandwidth of 250KHz. Frequency coverage is 138MHz to 4.4GHz (which will no doubt tell you which Analog Devices chip is being used). I was looking at the "RF section level diagram", Fig 10-10 in the TR4172 manual, and thinking how much of this I may be able to verify?

I am very interested if you can post or mail me some of the details you have found. Here in Cyprus it gets quite warm (it was 36C last Sunday) and I have found that in a number of instruments that have "plastic foam", the foam has turned to sticky tar. (This includes professional kit from Racal, B&K and HP as well as amateur items such as my KW2000 with its mechanical IF filter supported with plastic foam). Acetone is the only thing that I have found to clean the mess but it also dissolves many wanted items!

G0HZU_JMR 23rd May 2015 5:18 pm

Re: Spectrum Analyser TR4172
Hi Brian
I'm very busy over this weekend but I'll try and find time to post up some info. However, what you must NOT do is open up the first IF module (that sits under the mixer box) and touch any of the PCB traces. Especially around the IF amplifier section where there are some little blocks of absorber stuck to the PCB.

I found the same issue with softened copper traces that I found in the attenuator section and I think the glue they used to hold down the RF absorber ages or cures badly in terms of becoming a chemical hazard.

On my IF1 unit this glue had attacked one of the printed bias resistors in the active (16mA) bias circuit to the IF amplifier and slowly eroded it. The effect was that the resistor suddenly went up in value a lot and the IF amplifier lost its power supply. The module still biased it at 16mA but the voltage at the amplifier was down at about 200mV!

Also, I think this glue has caused accelerated ageing/corrosion to the fasteners and connections in the IF1 module. They go VERY rusty like they have been underwater for a few years. Also, the connections from the SMA launchers to the PCB are done with tiny ribbons of gold? metal and the connection to the SMA centre can corrode here (the SMA centre corrodes rather than the gold ribbon) and this can break the connection or make it unreliable. There's no other corrosion like this anywhere else in either of my analysers so I blame the glue...

The good news is that the IF amplifier device survived in my analysers and you just need to solder in a SMD resistor in place of the printed resistor if yours has the same fault as mine.

But the copper microstrip on this PCB seems to go very soft. Almost like rotten paint on a car. So if you touch it or try and scrape any residues from it, it will lift up and fall to pieces like it is thousands of years old!

So the fix is easy but you have to do the whole thing like it was surgery in an operating theatre because one slip means the copper traces are gone... They can't be stuck down again like regular copper tracks because they seem to go very soft and fall apart.

I doubt that your mixer will be damaged but I did find the original manufacturer's part number for it and I think they are still available online (but not from Advantest)

i.e. this is not an Advantest part number but the real part number for the diode ring.

It's a VERY strong mixer with 8 diodes inside and the LO drive level is about +23dBm so you may be OK and your mixer will be healthy.

I'll dig out my documentation and post up the part number and a few internal pictures when I get a chance.

G0HZU_JMR 25th May 2015 12:44 pm

Re: Spectrum Analyser TR4172
I found my old notes on the mixer and the part number is DMJ4708 which also has an HP equivalent part 1906-0279 according to some sources.

I think Alpha (now renamed to Skyworks) used to make/sell the DMJ4708. There are a few US retailers selling new/old stock online but not for overseas buyers.

Patience is probably your best bet here. If you keep searching you may find one cheaply. Or maybe get someone in the US to buy one for you.

However, I'd be surprised if the mixer is dead.

Here's a couple of faults I would consider more likely than a blown up mixer.

IF1 amplifier lost bias voltage due to eroded (printed) resistor on the active bias board.
Corroded/broken connection to one of the SMA connector centres inside the IF1 module.

Brian G8MUE 25th May 2015 11:34 pm

Re: Spectrum Analyser TR4172
Thank you G0HZU_JMR for the helpful response. Yes I did manage to get a quote for the Skyworks product but the minimum order was 100 off for about £700. Thanks for all the warnings about the PC tracks in the 1st IF. I was once involved in the offshore oil business and sometimes asked to recover an instrument which had flooded with sea water. Often this was possible but very often the repaired item would fail in 3 to 6 months through corrosion of the PCB or other components. Your post should keep me out of mischief for a while.

G0HZU_JMR 29th May 2015 1:21 pm

Re: Spectrum Analyser TR4172
2 Attachment(s)
Here's a couple of images of the IF1 amplifier device.

The IF1 amplifier is marked K in a 35 micro X package and I think it is the same as Q16 on the RF board = 2SC2150.

The first image shows all three bits of absorber and the second shows the printed resistor (arrowed red) that sits under the middle bit of absorber after the absorber is removed. This resistor had been attacked by the glue and had gone very high in resistance. It was also very faint as it seemed to have been eaten away.

The microstrip track arrowed in yellow is likely to be very soft as it also seems to get attacked by the glue. So it falls apart if touched with any tools. For this reason, don't touch ANY of the printed traces in the filter sections as these may be soft too.

You can also see how corroded the screws fasteners are. I think either the glue or the absorber sweats some form of catalyst that causes this corrosion.

This is a sealed unit and the same screws and metal tabs are used elsewhere in sealed parts of this same IF1 module but they are in sub compartments that don't have absorber or glue and the screws still look shiny.

So I don't think there's a dissimilar metal issue causing the corrosion.

To fix mine, I replaced the printed resistor (arrowed in red) with an SMD equivalent. I found a model for this type of transistor and modelled the stage for gain and noise figure on Agilent Genesys and found that the optimum bias point was about 2.5Vc. Biasing it at 5V Vc degraded the gain and the noise figure and I proved this with tests on the real module. With the corroded printed resistor the bias point was down at a tiny fraction of 1V because the resistance had gone quite high and this caused the stage gain to collapse. On my second TR4172 analyser the resistor wasn't as degraded and this still had reasonable performance and Vc was something like 1.5V.

The circuitry on the little piggy board is the active biasing network that biases the 2SC2150 device at a constant current of about 15mA.

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