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Marconi 2945 Spectrum Analyzer Problem




 
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Author Topic: Marconi 2945 Spectrum Analyzer Problem  (Read 185 times)
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WA2SQQ
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« on: November 07, 2018, 08:06:53 PM »

I just acquired 3 2945’s that ha e been sitting on the shelf for several years. All 3 have the same intermittent problem - they fail the RF level self tests. Each test shows -73.1 dim.  The manual describes self test as internally connecting the output to the input. I’m thinking they have a dirty connection somewhere. Without a schematic, I’m work blind. Anyone have any experience with this model?
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WA2SQQ
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« Reply #1 on: November 09, 2018, 03:56:05 PM »

Here’s an update that will hopefully help someone in the future. I accidentally found a post from an old friend who had the service manual. When he asked what the problem was he told me it was a common problem. There are two modules used for the “self test” mode. Marconi did a shoddy job soldering the center conductor to the PCB. I opened it up and sure enough both were barely soldered. This only effected the “self test” which explained why these have been in service without any problems.

Remove the bottom PCB to access the two small shiny silver modules. In the photo, they are marked with the orange dots. The two brass screws hold the modules to the chassis. Remove the cables. Once the modules are removed, carefully ONLY REMOVE the two bottom screws from each connector. Next, remove the multiple screws from the module’s perimeter. CAREFULLY Remove the BOTTOM cover. The problem is, that the connector is only held in place by a very thin connection which breaks loose. Resolder the connection, reassemble it, and it works just fine! I included a photo of how the connector becomes disconnected. Check both modules.

Time to find new homes for them!


* Marconi Interior 01.jpg (3240.1 KB, 2000x2000 - viewed 41 times.)

* Marconi Interior 02.jpg (2510.1 KB, 2000x2000 - viewed 47 times.)
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