[R-390] Troubleshooting Question

Chuck Kembring kembring at epix.net
Tue Nov 2 18:57:50 EDT 2021 

People tend not to consider the simple fuse in the circuit.
I spent a significant time in my career in the nuclear power industry and we could only use fuses from a specific manufacturer but also down to the specific manufacturing facility due to the audited manufacturers quality program.
That focus didn’t come about by chance.


Sent from my iPhone

> On Nov 1, 2021, at 5:12 PM, frledda at att.net wrote:
> 
> 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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