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42-1008 SHORTWAVE BAND SILENT - Printable Version

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RE: 42-1008 SHORTWAVE BAND SILENT - codefox1 - 01-14-2014

Try some Deoxit-5 spray. You can get it online or at any music instrument store. SSSSpray, let dry overnight.

Do not abrade contacts of modern switches with erasers, as they only are plated with a microscopic amount of silver. Old timers used to swipe a dollar bill twice between contacts to teach relays how to behave.

RE: 42-1008 SHORTWAVE BAND SILENT - davidff - 01-15-2014

Success!!, the cleaning (again) of the switch, and cleaning the inside of the antenna terminal area as well as tightening the screws where the antenna wires attach, and SW came to life in a big way. Many thanks to all of you for your helpful suggestions. If I went ahead and tried to remove the oscillator coils as I had originally planned, I would have ruined everything. Now on to the BOL phono.

RE: 42-1008 SHORTWAVE BAND SILENT - morzh - 01-15-2014

The key to a successful troubleshooting is eliminating the most likely and the simplest possible reasons first. And doing it in earnest. Such as if you clean the switch, clean it well.
Then your life will be much easier.

RE: 42-1008 SHORTWAVE BAND SILENT - PAradiogeek - 01-15-2014

Using Brenda's logic, if he is able to receive even one SW station, then isn't the band switch working?

If the station that you are able to receive is all the way at one end of the dial (either high or low), then to me, the problem is somehow related to the tuning. Possibly a trimmer or padder cap for either the antenna or oscillator has failed or been shorted and shifted the tuning range correspondingly. As a test of this, are you able to hear that one station's call sign and/or frequency? If so, does that match 'where' the station is being received on the dial?

My $.02 anyway.

Jon

RE: 42-1008 SHORTWAVE BAND SILENT - hsusmann - 01-15-2014

Sometimes if you have a dirty band switch you will only hear one or two stations because there is so much attenuation somewhere in the circuit that you only hear the really really strong ones.

I find that you can identify a dirty band switch by rocking it back and forth while listening and if it's dirty you will hear crackling and a noticeable change in volume levels as you make/break whatever bad contact is in there.

Can you monitor the front end grid voltages with a DVM as you rock the band switch back and forth? You might be able to detect a bad contact by monitoring the AVC voltage at the grids. If it's jumping around you may have a dirty switch. A conventional analog volt meter is best for this, not a DVM necessarily.

My 2 cents for what it's worth also!

Herb S.

RE: 42-1008 SHORTWAVE BAND SILENT - PAradiogeek - 01-15-2014

Oops, my bad. Didn't see page 2 and that it was already solvedIcon_sad Still surprised though that the switch was the culprit. Live and learn.

Jon

RE: 42-1008 SHORTWAVE BAND SILENT - morzh - 01-15-2014

Jon

If you look back you will see the switch was everyone's very first culprit.

RE: 42-1008 SHORTWAVE BAND SILENT - PAradiogeek - 01-15-2014

Yes, I saw that.

I think that when I was thinking of the switch, I was thinking of it as just a switch, i.e. an ideal switch that is either making a connection or not. I guess when talking about switches that are 60, or 70 years old, I have to account for the fact that, due to oxidation and/or dirt and grime buildup, it is possible that it is acting more like a resistor when it is 'on'. Is that the correct way to think of it?

Jon

RE: 42-1008 SHORTWAVE BAND SILENT - morzh - 01-15-2014

More or less.

RE: 42-1008 SHORTWAVE BAND SILENT - PAradiogeek - 01-15-2014

Got it. Thanks!

RE: 42-1008 SHORTWAVE BAND SILENT - hsusmann - 01-15-2014

Either acting as a resistor or acting as a capacitor.
Sometimes I think the switch contacts plus the wires going
to the switch can leak enough signal through just from the
stray capacitance to hear a faint signal.

RE: 42-1008 SHORTWAVE BAND SILENT - morzh - 01-15-2014

To be honest, having spent most my life in electronics and a sizable part of it in troubleshooting it, I no longer think of components as something....it is some mixed-up common picture in which when there are certain symptoms I have some intuitive image of something that I cannot explain that just tells me "look there".

Same was happening when I had to debug embedded C-code (that was long time ago) - I looked through the code (someone else wrote it), looked at what was happening and then I just looked in a certain procedure.

I don't know how to explain it - but it is associative, I would not be able to tell how it happens. Of course when I find the problem I probably can explain why it was happening, but not the way I found it.

I guess at some point having enough experience in something one starts thinking on a system level.

And the interesting thing is, when this level comes, one no longer has to even know how every single component functions exactly. For example, I do not have much experience with tubes and the schematic solutions using tubes, my lifelong experience is transistors and then microchips, analog or digital. At some point though (except for the part where you get zapped) they are the same.

So, for example, in this particular case I did not think of switch as a resistor, capacitor, bad switch etc.
I just looked at the common picture and some invisible finger in my brain (no, not the middle finger) pointed to the switch. That was it.

Or in Puh-Pow's case, the tube I pointed to first (and the idea this or the next one) is bad despite having been tested.....there was a picture and it did not fall in a certain pattern, so this tube was sort of standing apart, and so I pointed at it first and to the next one as the second possibility. Again, I did not analyze much - it was intuitive.

And, no, it is not a 100% - sometimes you have to analyze on component level.

RE: 42-1008 SHORTWAVE BAND SILENT - Eric T - 01-18-2014

Morzh- he is THE ONE:

[Video: http://www.youtube.com/watch?v=zYwdzYC3uUc]

RE: 42-1008 SHORTWAVE BAND SILENT - BrendaAnnD - 01-18-2014

IIRC, I said that if he was getting even one SW station, the LO was working. Didn't mention anything else about causality.