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- Опубликовано: 17 июл 2019
- I begin to repair a Marconi 2435 Frequency Counter, I find that channel B is mostly OK, but channel A doesn't work properly.
The damaged channel A section doesn't have any circuit diagrams in the service manual so I replace visually bad and suspected to be bad parts inside the shielded box of channel A and replace parts of the power supply.
Due to the amount of video I recorded working on this I have split it into 2 parts, this is Part 1, Part 2 can be seen here: • 🔴 #601 Marconi 2435 Fr...
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It is great to have the original manuals and well worth the money when doing a repair. Down conversion is a common arrangement in higher higher frequency and cost units like the Marconi. You just reminded my about that high resolution HP counter I half fixed. I cut the tantalums out just didn’t get around to refitting them. Sole destroying but you really have to change them all and the main smoothing and check for ripple on the rails.
AllTheGearNoIdea
I agree, the roadmap of a schematic makes clarity of the utter mess of a circuit layout :-D
But some diagrams look like the drawer was on lsd or similar drug when drawing them, mad diagrams lol.
zx8401ztv I think CB drawing are awful apart form the ones in those SAMS Photofact manuals they are like works of art. The Marconi drawing will be good.
Yes they are, i think modular sections with input/output labels just look simpler.
Then you can test a block one at a time.
AllTheGearNoIdea - I don’t mind cb diagrams, you get used to where they put everything and can find stuff easy enough.
I feel special because your Fix-It Friday's are my Fix-It Thursday's it's like I'm seeing defpom a day early
Its Thursday for me as well in rainy Brazil
Time travel!
Baby tants with values under 1uF simpler to replace with Wima MKF film capacitors, 0.47uF 63V is around the same size, similar enough footprint to fit and in most cases the height is fine as well, or use green dipped mylar capacitors. Close enough ESR wise, and better pulse handling ability.
Great work, can't wait to see part 2! For tough old/crusty rosin I use acetone - a solvent available at most hardware stores here in the states. You just have to keep it away from most plastics! Once the rosin is softened I use alcohol to remove it. You realize that by breaking that seal you have voided your warranty ;-D
Love Marconi gear. My 2019a I bought 5 years ago is great.
Getting a wet slug tantalum backwards is a lot more interesting. They go bang quite violently, as they pop only over 180C case temperature, where the solder melts.
As test engineers we used to tape a tant under the work bench of fellow engineers and when they were in deep thought reverse bias them with a psu. sounded like a gun shot between your legs? elf and safety was not a phrase used much then if at all.
I always test ALL caps and resistors and also any diodes with the diode test in multimeter. Sometimes it takes a while to do that. But anything I thus find gets replaced. Ive also taken out transistors and popped them in one of them $5-10 testers.
Ahh the evil tantalum beads wa wa wa lol :-D
There was a blue one in the squelch circuit of the uk 27/81 cybernet board, they blew up with psu spilkes.
I bunged in a normal electrolitic, always worked :-D
What is your temp on you're desoldering gun please?
😊
I have seen many dipped Tantalum's in test gear fail in the complete absence of noise or ripple on the main PS. 25% headroom for example, 20V rated cap riding on a 15V rail. What is really weird is that I have not yet encountered a wet-slug tantalum failure. I think it's a reliability, cost and end of life issue chosen by the manufacturer.
I have a 78 too :)
Marconi was sold to Aeroflex which was then bought by Cobham.
Next to the two 1000u/25V, you have two ROE brown plastic elyt caps. That model is notorious for going bad.
Edit: Ah good, you found them
Agree there. Had a ton in my Rohde and Schwarz sig gen, all leaking electrolyte.
thulinp - yeah o had come across those before when I fixed a Rohde & Schwarz SPN Generator, I did some videos on it, about 2 years ago.
is it a project or a challenge lol
Not changing the other Tants will drive you mad,every little flicker or wobble your going to be saying to yourself is it the Tants lol
An Englishman in Brazil - it’s fine after I got it fixed at was fine, I ended up selling it as I didn’t really need another counter