[R-390] Troubleshooting Question

Mon Nov 1 17:12:17 EDT 2021

We did see those kind of failures all the time on high power RADARs.  

Best, Francesco K5URG

-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On Behalf Of Alan Victor
Sent: Monday, November 1, 2021 3:50 PM
To: Jim Whartenby <old_radio at aol.com>
Cc: r-390 at mailman.qth.net
Subject: Re: [R-390] Troubleshooting Question

Hi Jim.

Good for you to find it and I put on the list of weird stuff that happens!
It is amazing how the EE in the CAN like DeOxit and so on fixes stuff that a lab full of test equipment may not catch!

Alan

On Mon, Nov 1, 2021 at 3:41 PM Jim Whartenby via R-390 < r-390 at mailman.qth.net> wrote:

> Alan
>
> Could be.  Evidently, the "semiconductor" became more of an insulator 
> over a period of a few minutes.
> Obviously my track record of guessing is not up to par and my physics 
> and chemistry background is dismal but I would hazard a guess that it 
> has to do with temperature.  Sort of like a PTC Thermistor, the hotter 
> it gets, the higher the resistance.
>
> Jim
>
> All we want are the facts, ma'am.
> Joe Friday on  Dragnet, remember him?
>
> Too much agreement kills a chat.  E. Cleaver
>
> -----Original Message-----
> From: Alan Victor <amvictor at ncsu.edu>
> To: Jacques Fortin <jacques.f at videotron.ca>
> Cc: Jim Whartenby <old_radio at aol.com>; r-390 at mailman.qth.net
> Sent: Mon, Nov 1, 2021 1:16 pm
> Subject: Re: [R-390] Troubleshooting Question
>
> I suspect it is even more bizarre than that.... Oxidation on the fuse 
> metal contact forms a semiconductor junction, the net result is some 
> rectification of the line V and not simply an IR drop! It would have 
> been neat to see if the fuse interconnect was hot or if a scope would 
> have displayed the rectification.
>
> Alan
>
> On Mon, Nov 1, 2021 at 11:15 AM Jacques Fortin 
> <jacques.f at videotron.ca>
> wrote:
>
> Well, that happened to me before…
> In my case, it was the fuse itself ( a slow-blow one).
> It behaved as a breaker.
> Took days to find.
> It was not in a R-390 however.
>
> 73, Jacques, VE2JFE.
>
> Le 1 nov. 2021 à 11:00, Jim Whartenby via R-390 
> <r-390 at mailman.qth.net> a écrit :
>
> Roger
> I was concerned that the issue was a failed switch.  Surprised that 
> the problem was simply a dirty fuse contact.
> Just goes to show that experience pays off, good call Jacques!
> Jim
> Too much agreement kills a chat.  E. Cleaver
>
> -----Original Message-----
> From: Rodger via R-390 <r-390 at mailman.qth.net>
> To: R-390 at mailman.qth.net
> Cc: 'Jacques Fortin' <jacques.f at videotron.ca>
> Sent: Mon, Nov 1, 2021 9:35 am
> Subject: Re: [R-390] Troubleshooting Question
>
> Thanks to all for your responses on my power supply troubleshooting 
> question.  Had a taken a quick look at the schematic before posting, I 
> would have realized there was only a few things that could have caused 
> this problem.  After tacking wires onto the power transformer to allow 
> for measurements to be made on both primary and secondary side of the 
> transformer, I was all set to "catch" the problem.  When it next 
> happened, I was losing power to the primary side of the transformer.  
> That left 2 things, both which had been mentioned by list members, the 
> fuse and the line filter.  The FUSE was the culprit as Jacque 
> suggested.  I didn't even have to replace the fuse as it wasn't blown, 
> but just had to twist it around in the socket a few times.  Problem 
> solved.
>
> I am amazed that something as simple as dirty contacts between a fuse 
> and the fuse holder could cause a problem with such a repeatable symptom.
> Before I started troubleshooting, this problem had recurred, probably 
> 25 to
> 30 times and each time was exactly the same.  The 390 worked for about 
> 2 minutes and then shut down.
>
> Thanks all for your input and troubleshooting suggestions.  Lots of 
> lessons learned, including ask this list first!
>
> Thanks,
>
> Rodger
>
> -----Original Message-----
> From: Jacques Fortin <jacques.f at videotron.ca>
> Sent: Saturday, October 30, 2021 10:42 PM
> To: rodger_adams at yahoo.com
> Cc: R-390 at mailman.qth.net
> Subject: RE: [R-390] Troubleshooting Question
>
> Rodger, you will surely found my advice strange, but...
> Just replace the mains fuse with a new one and retry.
>
> 73, Jacques, VE2JFE
>
> Hey All,
> I have an R-390 (non A) that has developed the following problem.  
> When I turn it on, it warms up and works normally for about a minute 
> or so.  Then without warning, it shuts down.  Lights out, no B+, etc.  
> It does the exact same thing every time I turn it on.  Any thoughts on 
> where to begin troubleshooting?  How to easily isolate the B+ from the modules, etc. ?
> For
> the minute that it's on after warming up, the B+ reads 185 volts.
> Thanks in advance for any advice.
> Rodger
>
>
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