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The whistle control on this Lionel Model RW tranformer isn't behaving like my other transformers.  The whistle (postwar) will sound when the button is partially depressed but won't continue to blow when the button is fully depressed.  When the button is half depressed, there is 7.1v DC but all DC voltage drops out when the whistle button is fully depressed.  There should be 0.5v of DC when the button is fully depressed to keep the whistle relay engaged and it's not there.  The resistance wire shows continuity and is about 3 ohms.  The NTE 5812 diode was in place when I bought it, although still with the copper oxide disc in place, which I removed and resoldered the diode.  I don't know if it worked correctly before I removed the copper oxide disc.  Photos of voltages and position of whistle button below.  Anybody seen this before and can suggest the fault?  What to check next?

Whistle button not pushed -  9.5v AC from A-U terminals

03 Whistle up 9.5v AC [Medium)

Whistle button half way down 7.1v DC (& 15.7v AC not shown)

04 Whistle part way down 7.1v DC [Medium)

Whistle button fully depressed 0v DC  (& 15.7v AC not shown)

05 whistle fully down 0v DC [Medium)

RW Transformer Wiring Schematic

Attachments

Images (4)
  • 03  Whistle up 9.5v AC  (Medium): Whistle button not depressed - output 0v DC and 9.5v AC
  • 04  Whistle part way down 7.1v DC  (Medium): Whistle button part way down 7.1v DC and 15.7v AC
  • 05 whistle fully down 0v DC   (Medium): Whistle button fully depressed 0v DC and 15.7v AC
  • RW Transformer Wiring Schematic
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I'd find it hard to think the switch is the problem. As soon as the switch is half way down, it's connecting the diode ( via point A) into the circuit and that works.  The main thing that happens when the button is fully depressed is that it adds the balancing resister (9) when point C is connected.  The diode is dropping out - why?  I have tried pushing on the arm of the copper slider (switch) overlying point A to see if it was losing contact but it doesn't seem to make any difference.  In other words, the extra pressure doesn't suddenly make the copper slider connect to point A and add the DC back, so I don't think it's a worn slider/switch that's the cause.

@R Lamparter posted:

... When the button is half depressed, there is 7.1v DC but all DC voltage drops out when the whistle button is fully depressed.  There should be 0.5v of DC when the button is fully depressed to keep the whistle relay engaged and it's not there

This has to be tested with the rated load. Without a load, yes, all of the current will go around / skip the rectifier.

I was reviewing this again.  I had forgotten that the whistle tender's relay wouldn't stay latched with the button fully depressed which is why I started the thread.  Now it's staying latched and sounding with the button fully depressed.  I don't know what changed, but it's working now.  I tried three or four other whistle tenders and the transformer has no problem making any of them sound.

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OGR Publishing, Inc., 1310 Eastside Centre Ct, Ste 6, Mountain Home, AR 72653
800-980-OGRR (6477)
www.ogaugerr.com

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