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Old 12th Feb 2021, 7:50 pm   #1
Dave Moll
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Default Vanguard 10E (4005)

I have recently acquired a Vanguard 10E telephone (also known as telephone 4005) which initially I thought was in working order, but having left it plugged in I found it was trying to make calls while left on hook. Having plugged it into my telephone tester I found that the "line seized" indicator was flashing away randomly, mostly with a loop made but fairly rapidly flashing off - with the inevitable result that this these disconnections were being interpreted as dial pulses (as confirmed by random digits appearing in the "dialled digit" display).

Having opened the set up, I found that the cradle button (which operates the gravity switch) fell out as its return spring had come unhooked, and I thought this had turned to be a simple problem to solve, especially as it worked when I plugged it back in after re-attaching the spring - releasing the line when I pressed the button and seizing it when released. I then reassembled the 'phone and found that the problem had returned even though the cradle switch was now working correctly. After opening up once again, I confirmed that the button was still correctly attached, but the problem persisted.

Any thought about possible causes of this problem?

Edit: I should add that I have checked the operation of the switch operated by the cradle button and it conducts when not operated (on-hook) and is open-circuit when released (off-hook).
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Last edited by Dave Moll; 12th Feb 2021 at 8:09 pm.
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Old 13th Feb 2021, 1:43 pm   #2
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Default Re: Vanguard 10E (4005)

Having fully dismantled the instrument, including disconnecting all internal plugs, to give the circuit board a closer inspection (and finding no visible problems) I reassembled everything and it seems to be working fine now. I can only assume there was some bit of conductive foreign matter somewhere causing an intermittent short and the dismantling has dislodged it.
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Old 14th Feb 2021, 4:51 pm   #3
AndiiT
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Default Re: Vanguard 10E (4005)

Hi, is the phone being used in an environment where there's a degree of humidity or condensation?
I ask because the Vangaurd instruction manual stated that the phone was not suitable for use in somewhere such as a kitchen where there may be large(r) variations in temperature and humidity.

Just a thought

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Old 14th Feb 2021, 6:00 pm   #4
Dave Moll
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Default Re: Vanguard 10E (4005)

I'm using it in the office of my centrally-heated house, but whether it had been subjected to humidity prior to delivery I don't know. As I say, the problem has gone away, so it may be that it did have damp that has now dried out.

I now have a frustrating new problem in that the button to select the loudspeaker function has stopped working. When I open up and press the stud over the circuit board (containing a conducting disc that bridges two contacts on the board) it works fine and after reassembly continues to do so for two or three presses of the external button before stopping again. The problem has to be mechanical in that either the external press isn't being transmitted through to the stud or the disc isn't bridging the contacts correctly, but is has been put to one side for the moment to get on with other matters.
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Old 17th Mar 2021, 4:23 pm   #5
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Default Re: Vanguard 10E (4005)

I think I've finally identified the problem with the loudspeaker switch. It was indeed mechanical.

The external button presses onto a switch on the circuit board to toggle the loudspeaker function on and off. It would appear that the circuit board is not held sufficiently solidly in position so that after a few presses it has slipped off the peg to hold it in place and the button no longer reaches far enough to operate the switch.

To circumvent the problem I have attached a stciky pad to the underside of the circuit board so that it is held slightly raised (but still allowing sufficient travel for the button). This seems to have restored functionality.

I'm not sure whether this is a design fault or whether there has been damage to the peg so that it doesn't secure the circuit board as well as it should. There is no visible sign of damage.
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