Author Topic: W&G sna-20/23 spectrum analyzer repair (Read 13964 times)

Pude · « **Reply #75 on:** October 03, 2022, 04:50:17 am »

And here's my B-drive zipped including calibration data.

dxl · « **Reply #76 on:** October 03, 2022, 08:53:59 am »

With the H series software i see accesses to 9000:XXXX and D0000:XXXX segments, which might be the DSP. Any BIOS settings that might interfere with these ranges? (Not sure whether the old units are using the same range)

dxl · « **Reply #77 on:** October 07, 2022, 05:42:28 pm »

Received my unit today. As expected, no way to repair that board. Googling for the type suggested that "CSS Industrie Computer GmbH" seems to be the manufacturer. Not sure whether that's also true for the 386SX based boards.

https://www.industriebedarf.de/firmen/kaufbeuren_css_industrie_computer_gmbh.htm

Pude · « **Reply #78 on:** October 07, 2022, 05:53:03 pm »

Quote from: dxl on October 07, 2022, 05:42:28 pm

Received my unit today. As expected, no way to repair that board. Googling for the type suggested that "CSS Industrie Computer GmbH" seems to be the manufacturer. Not sure whether that's also true for the 386SX based boards.

My mainboard is done By W&G inc USA.

dxl · « **Reply #79 on:** October 10, 2022, 04:26:37 pm »

Some progress on my side...

With a lot of googling, i figured out that the Wandel & Goltermann ANT-20 "Advanced Network Testers" are using the same types of Motherboard. They existed in a lot of varieties from 486DX2 (the one i want, because it's the same as the one in the SNA) up to Pentium II boards. So i searched on ebay for such a unit. Unfortunately you cannot really see from the outside the exact type - the only indication is the location of the ps2 connectors. So i bought one for 50 EUR + the same amount of shipping. Luckily it had exactly that 486DX2 motherboard, just with an addtional adapter board for the TFT/DSTN display.

Putting it into the SNA, i was a bit disappointed because nothing was happening on screen when the unit was turned on. Measuring voltages showed that the 5V power supply rail measured only 1.8V. Turned out that the old motherboard had blown the fuse in the power supply - replacing that one made a picture appear on the external screen. The internal EL displayed just showed the usual Zebra stripes. I played with the Shadow/Cache settings, but that didn't had any effect. I then noticed a 'Simultaneous Display on both screens' option. I enabled that option, and the EL display showed a picture. Unfortunately only until the next boot, now i cannot get a pictures any more, except the Zebra stripes.

The display also has quite a lot missing lines - not sure what to do about them. I never worked on such displays, maybe it's a driver chip that can be replaced, i just don't know.

The Spectrum Analyzer section seems to be fully working, which is the important part - i put in a 1, 10 and 20GHz signal, and it all looked good.

dxl · « **Reply #80 on:** October 10, 2022, 08:24:22 pm »

ok, the display is definitely not repairable - someone applied way to much force (i have no idea why the metal frame next to the floppy drive is bent - it's hidden inside of the front panel)

manicdoc · « **Reply #81 on:** October 10, 2022, 09:32:40 pm »

use some clear curing epoxy on that damaged area to ensure it won't shatter. aim to fill level with everything else.

Pude · « **Reply #82 on:** October 11, 2022, 05:10:31 am »

I'm also in the process to replace this 35670A screen using RGBtoHDMI and modern screen unit.
I got this HP from Lohja, Finland which is the town where Finlux once made these EL-displays. I wonder if any former employees have some old stock somewhere.

SNA-33 also has Finlux screen originally.

dxl · « **Reply #83 on:** October 11, 2022, 06:52:29 am »

Interesting, didn't knew that HP used the EL screens in the 35670A...

dxl · « **Reply #84 on:** October 11, 2022, 07:05:00 am »

Quote from: manicdoc on October 10, 2022, 09:32:40 pm

use some clear curing epoxy on that damaged area to ensure it won't shatter. aim to fill level with everything else.

The problem is not the mechanical stability, but the electrical "wires" which are on the glass and broken.

dxl · « **Reply #85 on:** October 12, 2022, 05:56:23 pm »

I zipped the firmware of my SNA-33 and uploaded it to ko4bb. It's a revision G model, so different from the H model we already have. I tested whether the H software runs on a G model, and it does.

dxl · « **Reply #86 on:** October 17, 2022, 04:03:37 pm »

One thing that wonders me on my unit is whether the fan is working. The one in the Power supply seems to be working, but the other one next to the mainboard in the back doesn't do anything. I haven't checked the schematics whether that one is temperature controlled or so.

Pude, Gerhard, is that one working on your units?

Qw3rtzuiop · « **Reply #87 on:** October 17, 2022, 04:15:15 pm »

Quote from: dxl on October 17, 2022, 04:03:37 pm

One thing that wonders me on my unit is whether the fan is working. The one in the Power supply seems to be working, but the other one next to the mainboard in the back doesn't do anything. I haven't checked the schematics whether that one is temperature controlled or so.

Its temp controlled. Heat up the marked NTC/PTC(?) and it should start spinning.

dxl · « **Reply #88 on:** October 17, 2022, 05:07:01 pm »

Thanks, the fan is working. I applied some heat and it started spinning. Odd place IMHO given that the power supply has its own fan, and that area doesn't get much airflow from the fan.

dxl · « **Reply #89 on:** October 17, 2022, 07:15:12 pm »

I was wondering why the sweep update rate is slower than on a HP8563E. With the information from the map files i partially reversed the communication protocol between the software and the dsps. It's quite interesting that the sweep only takes 25ms, but the processing between sweep takes almost 75ms. Look at the green and blue cursor lines in the listings, this is one sweep.

I wonder whether this could be improved with a more modern mainboard.

dxl · « **Reply #90 on:** November 22, 2022, 10:15:06 pm »

I "fixed" the display problem on my unit now by replacing the EL screen with a 8.4" 800x600 TFT screen. The firmware needed a few tweaks to recognize the 640x350 video mode, but otherwise it's looking ok. Not as sharp as the EL display because the image gets scaled, but still ok. It also has the nice side effect of adding color. The size of the panel is almost the same as the original one, it's a bit more in height, and about 1cm less in width.

alexturner · « **Reply #91 on:** November 24, 2023, 03:27:59 am »

I had a good year or so with mine working immaculately and today I went to use it and noticed that it's deaf

Not sure where to start looking, I've tried frequencies up to 1GHz (limit of my source), have attached a Log Normal antenna and nothing. Changing attenuators makes no change, any ideas where to start with this? This has been a taxing instrument to own so far

dxl · « **Reply #92 on:** December 05, 2023, 08:14:02 pm »

Can you post a picture of the screen in full span mode? Do you see the normal noise floor?

alexturner · « **Reply #93 on:** December 18, 2023, 10:24:46 pm »

Hey dxl - It sure seems as if it's the normal noise floor in full span. How come?

aseok · « **Reply #94 on:** February 19, 2024, 04:33:38 pm »

Following is picture of sna-20 2101b board, the inductor was blown and removed (white blank part of pcb) also at least some other damaged/blown parts visible. Is there any chance to fix this? is it worth the effort at all?

alexturner · « **Reply #95 on:** February 24, 2024, 05:34:36 am »

Possibly, the schematics are available on the web.

alexturner · « **Reply #96 on:** February 24, 2024, 05:52:49 am »

I spent some time with it and found that the power supply to the YIG oscillator had a bad transistor, swapped and it came back to life. Lasted an entire day, and now it's giving me grief again. When it boots, it displays the preset band fine, then when the unit displays the "Calibration Active" message, the entire signal flies up such that the measurement base is on the 0db line and saturated noise above that.

Does anyone know what "Calibration Active" does in the unit? I've re-loaded my calibration data and checked the internal calibration reference, which is fine. Logarithmizer seems fine too given I see the trace on boot. I've recorded a short video here incase you have any ideas - not sure where to look at this point

https://youtube.com/shorts/tnBPF-xLFNI


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Author Topic: W&G sna-20/23 spectrum analyzer repair (Read 13964 times)

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