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Old 2nd Apr 2021, 6:54 pm   #161
Matt kd4pbs
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Default Re: Spectrum Analyser TR4172

Sorry guys - I've been swamped with some other projects as of late, and have not had a chance to visit you all. That's great news, Lex! I will certainly look there as well, and it sounds as if you saw the exact same thing with the 30MHz amp as I did. I finally called it a day on that one and moved on; I'm sure it's working fine. If something were bad, I'd see it at DC, or wouldn't be able to control the level through the amp, or would see lots of loss.
In the meantime, I did get some time to spend with the SpecAn, and got all of my extender bits in. The video game extender cables work, more or less. The leads are so long that it causes problems... the cabling is all unshielded conductors and are almost a meter long! I'll need to shorten those a bunch, but I actually do enjoy there being cables instead of a card. It makes it easy to lay the board on the table and work from there. For the smaller card edge cards, I did find an extender card. As such, I was able to go through part of the calibration - namely most of the stuff in the display chassis. What I found was that there were quite a few noisy trimmer pots, and I imagine this was causing some of my lock up problems. So far, between that calibration and finding a broken wire on that little YIG driver piggyback board modification, I am not having the lockup issues that I had before. Only one remains; with a signal in it or not, if I select a CF of 50.050MHz and a span of 500KHz, it freezes. I can do it all day long at 50MHz, or 50.1MHz. Even if I dial it into 50.050, it freezes. I haven't spun through the range yet to see if it freezes anyplace else. Quite aggravating.
I will certainly look closely at that filter section. I hope it is that easy.
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Old 12th Apr 2021, 6:59 pm   #162
SATOLEX
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Default Re: Spectrum Analyser TR4172

Hi all, I have fixed the broken inductor ground connections in the 206 MHz band-pass filter and have trimmed the amplifier-filter combination. This solved my 14 dB gain loss issue in the RF part, see picture . I have a gain adjustment margin of about +1.5 dB (cal. screw) and this is ok for the moment. I managed to do the auto calibration and for what I have seen so far is that it does not freeze anymore. I have trimmed the 206 MHz BPF based on the service manual instructions on page 11-65. According my paper manual version the maximum gain ripple has to be smaller than 0.3 dB, a symmetric response with a maximum level. The picture in the manual suggests that it has to be flat in a certain bandwidth but this not specified. Im not sure what the right response has to be, I assume a narrow bandwidth, see my picture. Jeremy do you want to perform one more measurement for me, please? You only have to connect the tracking to input-1 and press some keys. Im curious how your 206 MHz BPF response looks like.
Best regards,
Lex
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Old 12th Apr 2021, 7:42 pm   #163
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Default Re: Spectrum Analyser TR4172

I can dig out my TR4172 and try a few tests but I don't think my analyser IF1>IF2 block is the same as yours. I think both of my TR4172 analysers are the same as each other with similar serial numbers but I don't think they have the same 206MHz BPF technology as shown in the service manual. I assume mine is newer (but it could be the other way around).

When I had the original IF1 failure mode I did trace the signal path from the input to the 3.3MHz IF output at the back of the RF unit. Looking at the old internal images of my analyser the 206MHz filters are vertical with top adjuster screws. The filter cans stick out through the main lid, i.e. the RF block lid has square holes in it to allow these filter cans to poke out. In other words, my filters can be adjusted without removing the metal covers of the RF/IF block. I'm not sure my analyser has the two switched 30MHz BPFs at the 3rd IF either. It looks like the signal path of my analyser is quite different here.
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Old 12th Apr 2021, 7:51 pm   #164
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Default Re: Spectrum Analyser TR4172

See below for an image to show what I mean. I'm not sure which of my TR4172 analysers this is but they are both the same. This looks different to the images in the service manual.

The picture is a bit fuzzy but the circled area is where I think the 206MHz filter is located. I don't think I have any images with that cover removed.
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Old 12th Apr 2021, 8:19 pm   #165
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Default Re: Spectrum Analyser TR4172

I managed to find some internal images on a backup disk and these are probably of my main TR4172. The pictures are really fuzzy but I was in the middle of faultfinding so they were taken in a hurry. it looks like the camera didn't focus properly.

I've uploaded some of them here.

https://www.qsl.net/g/g0hzu//RF%20Tr...ctures/TR4172/

These show that this analyser is a bit different to the one shown in the service manual. If you look at all the images there are some piggy boards with printed filters on them in the LO section so this looks a bit bodgy in places to me.
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Old 12th Apr 2021, 9:34 pm   #166
SATOLEX
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Default Re: Spectrum Analyser TR4172

Thanks. You do not have to dig the TR4172 out but if you have it out one day and you have some time left Im still curious (or Matt). You do not have to open it, only connect TG to input-1 and press a few keys. No hurry!

Indeed, your RF part looks completely different than mine. I think that I have the same RF part version as Matt, the third mixer looks the same. For this moment the analyser is good enough for some hobby measurements. At a later moment I want to check the performance better and do some calibrations and more adjustments. This is nice to do in winter time. At this moment I have to focus on some other (home) projects. Jeremy, Matt and David thank you for the support! Mine is alive again and I'm happy .

Best regards,
Lex
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Old 12th Apr 2021, 10:03 pm   #167
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Default Re: Spectrum Analyser TR4172

If you list up the key presses for the test I can try and do the tests over the coming weekend.

One test you could do would be to measure the noise floor with 0dB attenuation at 50MHz on a 500kHz span. I have done this test many times over the years. I think I used to set the reference level to -30dBm for this test but when I select the 1Hz noise marker and turn on video averaging I always used to see -147dBm/Hz here. However, when I did this test a few weeks ago it was -146dBm/Hz so maybe it needs a fresh run at the cal/error correction routine.

Back in 2015 I did make up an excel spreadsheet to simulate the signal path for gain/loss and noise figure and IP3 performance and it does show -146dBm/Hz. This would have been based on stage gain/loss measurements I made when I had it apart.

Have you checked the condition of the internal backup battery? This lives on a PCB card in the top unit. See the image below. I think the original battery is under this grey cover but I can't remember what it looks like. I recall that mine had died and I fitted some rechargeables here. Note the amusing spelling 'BATTLY' in the image below.
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Old 13th Apr 2021, 6:13 pm   #168
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Default Re: Spectrum Analyser TR4172

No, I did not check the condition of the BATTLY. If I turn the analyser off and pull out the power plug for a while then I still have the calibration. I assume if I can readout the resolution bandwidth calibration it is still working. What do you think of these values? About the noise level, yours is much better. I have measured about -141dBm/Hz. During this noise floor measurement I observed an other issue. At a certain setting I saw repeating spurious tones in the noise floor and if I turned the marker readout off the spurious tones disappeared. Does this ring a bell to you Jeremy? Is this a problem in the display part? What I have mentioned before I have to check the analyser completely but that is a lot of work.

I have attached two pages out of the manual. You have to adjust the RF level in range, thanks.

Regards,
Lex
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Old 13th Apr 2021, 6:53 pm   #169
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Default Re: Spectrum Analyser TR4172

Yes, on my TR4172 the marker seems to introduce some strange spiky gating effects on the display trace under certain settings. Mine has always done this and I think the spare TR4172 does it too. I'm not sure if it is a fault but it doesn't look good when it happens.

Your calibration results look a lot more consistent than mine for the narrow RBW settings. I keep meaning to adjust the 7Hz and 10Hz RBW filters in mine. I usually see error corrections of 2.5dB for the 7Hz RBW for example.
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Old 14th Apr 2021, 4:09 pm   #170
Matt kd4pbs
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Default Re: Spectrum Analyser TR4172

Glad that your unit is working again, Lex! I am having the same "other" problem as you though... higher priority work in the form of home projects to contend with.
So far, I have been able to get through the calibration up to section 11-6-8 where I need to remove the tracking generator block for adjustment. I am debating whether or not to perform this, as to this point, the machine seems to perform very well. I was able to gain a couple of dB through the alignment procedures to this point. After I'm done doing some real work, I'll re-visit this just to see how difficult it will be to remove the TG block for calibration.
Edit:
I too saw the "BATTLY" and appreciated the Japanese humor in that. I bet the design engineer got a little giggle... I wonder if he/she was Japanese? Anyway, I had ordered these a while back and will be swapping with the original NiCd cells, which, incidentally, had not leaked and actually still would hold enough of a charge to keep the memory good for a couple of days.
https://www.amazon.com/4pcs-Coin-200...dp/B088G2393T/
Thanks a bunch for your help with this, gentlemen!
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Matt
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Old 1st May 2021, 4:08 pm   #171
SATOLEX
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Default Re: Spectrum Analyser TR4172

Hi Jeremy, my 'battly ' is also bad (no surprise). After a week the calibration is gone. Where did they hide the circuit board which you have showed. I want to have an idee where I can find it before I take it completely apart.

Regards,
Lex
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Old 1st May 2021, 6:36 pm   #172
SATOLEX
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Default Re: Spectrum Analyser TR4172

Found it, did not looking closely .

Regards,
Lex
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Old 5th May 2021, 1:24 pm   #173
Matt kd4pbs
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Default Re: Spectrum Analyser TR4172

Well, I buttoned her up, put all the panels back on, the screws back in, and got my son to helpp me heft the thing back up on the shelf above the bench, and surprise... it's exactly 10dB deaf.
Grr.
The saga continues, once I can get help to pull it back down to the bench.
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Old 7th May 2021, 2:15 pm   #174
SATOLEX
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Default Re: Spectrum Analyser TR4172

That is bad luck! I had the same with my IF1 module, after putting the analyser together it did not work anymore. In the beginning I thought that I had damaged the front-end. The 10 dB loss sounds like my loss problem. Check the inductor ground connections of the 206 MHz BPF in the RF part. Matt, I discovered why my LO2 power was too low. After tuning the LO2 chain I had more LO2 power. It is still less than yours but it is now +7 dBm at the output of the 1.84 GHz BPF which is going to the tracking generator. What I found in the manual is that this should be sufficient. Due to the higher LO2 power I also have more RF gain. So, relative to the -20 dBm calibration signal I have +3 .. -2 dB adjustment range. I also adjusted the 10 MHz time base reference and compared it with a 10 MHz GPS standard. I am still a little bit confused about the frequency reading. The -20 dBm reference is "exactly" 50 MHz if measured back with the GPS 10 MHz standard. The marker readout is telling me that the frequency is 50.0005 MHz. According the Freq counter function it is 50.002474 MHz and with Tuned Amp. Function (most accurate) it is 50.000000 MHz. Is this normal or do I have to calibrate other parts of the analyser?
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Old 7th May 2021, 4:00 pm   #175
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Default Re: Spectrum Analyser TR4172

Exactly 10dB suggests a stuck attenuator section or a programmable gain stage, or maybe a section in a log detector.

Nature doesn't normally do round decimal numbers.

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Old 13th May 2021, 8:43 pm   #176
Matt kd4pbs
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Default Re: Spectrum Analyser TR4172

David, I am thinking the same thing... Attenuator. Other pressing time wasters.. I mean... projects seem to have taken priority. I'll certainly report when I find the issue, but summer time is usually "anything but diddling with electronics bits at the workbench" time.
I, too have noticed an increase in sensitivity after re-tuning the RF section from the manual. I gained a few dB - enough that I actually don't need the amplification stage that I bodged in after the 1st mixer any longer. Still, I kept it in there and installed appropriate attenuators inline.
Lex, from what I can see of the 206MHz filter section, mine was nice and tight and solid.
This will be more interesting times spent fiddling after this summer for sure.
73, all-
-Matt
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Old 30th May 2022, 2:18 pm   #177
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Default Re: Spectrum Analyser TR4172

Thread reopened at member's request.
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Old 30th May 2022, 9:17 pm   #178
Alan Bain
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Default Re: Spectrum Analyser TR4172

Thanks to moderator for reopening! So I also have a TR4172 which is deaf 35db and interestingly the voltage measurements in the IF1 amp match those reported by Lex in #24 above (110mV CE of the RF device, and VTP3 around 7V instead of 10V, current draw from 15V supply 22mA). There was a black blob of epoxy over bias device and attempting to gently scrape this pinged off the device and a small capacitor to earth off to infinity and beyond, fortunately with minimal track damage. I have no idea what the capacitor value was but appears connected base to earth of the biasing transistor. Does anyone have any idea?

Fortunately no blobs of glued on absorber and no signs of track damage. This is an early Takeda-Riken badged model.

My resistors all look good and measure
R1=2180 ohm
R2=406 ohm
R3=10K
R4=4K7
R5=436 ohm

I imagine that a generic PNP SOT-23 like a BC857 should do - does anyone have any advice on what to use both as equipment and as solder for soldering it (I have a stereo microscope)? I'm not familiar with this sort of almost hybrid like board with chrome and gold layers.
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Old 31st May 2022, 6:49 pm   #179
Matt kd4pbs
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Best wishes with this, Alan. I have yet to find the round tuit to help me work on this some more. Lots of pressing projects in the past year have kept it dormant in the corner of the workshop/hamshack upstairs. Now if only I could convince my wife that it's more important than the honey-do list...
Also, unforunately it appears the YIG oscillator has gone out again on my trusty 8753D, so I've also lost the only piece of test equipment I had that I could press into service to generate the signals needed to troubleshoot this more. So, it's kinda on a perpetual standby until either I get the chance to fix it all or get fed up with it all and throw it all in the trunk of a person who could use it, in the trash, or in the lake as an anchor for my boat.
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Old 31st May 2022, 10:07 pm   #180
Alan Bain
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Default Re: Spectrum Analyser TR4172

I know the feeling about finding test gear for the test gear - I have a working MI TF2370 (too low frequency at 110MHz upper limit to help here) and a HP8558B but the 8444A tracking generator for that is not working (the 1.55GHz cavity oscillator insists on oscillating at 1.85GHz), so have been having to rely on harmonics from the HP8640B as my only suitable signal source! A nice handy VNA that was working would help a lot here...
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