741 Wall phone short circuit issue? - UK Vintage Radio Repair and Restoration Discussion Forum

Ryan_1993 · 28th Aug 2014, 8:10 am

Hello all I have just noticed a problem with my Ivory 741 wall phone. It has been working fine since I converted it on sunday, but last night I lifted the receiver and it was extremely quiet, dial tone barley audible. I have a double phone socket splitter and also have connected a bakelite 232 telephone. Out of curiosity I picked that up and the dial tone sound level is normal.

i have tried the master socket downstairs with all other phones disconnected the same results

I have swapped speakers off several other 746 models I have, same results. I did manage to get it to work briefly at normal sound level when taking the cover off the phone and jiggled the wires around, however, as soon as I put the case on and hung it back on the wall the volume level went quiet again. My guess is something could be shorting slightly?

Out of curiosity though is the printed circuit board in the desktop 746 the same as in the 741? as I would just do a straight swap over. I got a ivory 746 the same day as getting this.

I hope someone can help

Thanks Ryan

Nickthedentist · 28th Aug 2014, 8:28 am

I'm sure you're right, but could also be a crack in the PCB, a dry joint on one of its connections, one of the wires adrift on the ASTIC (transformer), the board being shorted out by the metal base and so on.

Another thing to check is that the dial contacts that short-out the receiver (earpiece) are OPEN when the dial is at rest.

And yes, you could swap the PCB to narrow down the fault if you wished.

Nick.

Ryan_1993 · 28th Aug 2014, 6:16 pm

bit of an update

I swapped out the circuit board and all seems fine, no idea what the issue was, but I guess something wasn't quite right with the board that was in it originally.

Dave Moll · 28th Aug 2014, 7:36 pm

Have you tried reassembling the 746 with the circuit from the 741? If so, has the fault now migrated to the 746?

If the answer is yes, then there is indeed a fault in the circuit board. Tracking it down wil be the next challenge.

If no, there was presumably a dodgy connection that has been been cured during the swap over by removing one set of connections and making the other.

28th Aug 2014, 8:10 am	#1
Ryan_1993 Hexode Join Date: Sep 2012 Location: Yorkshire, UK. Posts: 329	741 Wall phone short circuit issue? Hello all I have just noticed a problem with my Ivory 741 wall phone. It has been working fine since I converted it on sunday, but last night I lifted the receiver and it was extremely quiet, dial tone barley audible. I have a double phone socket splitter and also have connected a bakelite 232 telephone. Out of curiosity I picked that up and the dial tone sound level is normal. i have tried the master socket downstairs with all other phones disconnected the same results I have swapped speakers off several other 746 models I have, same results. I did manage to get it to work briefly at normal sound level when taking the cover off the phone and jiggled the wires around, however, as soon as I put the case on and hung it back on the wall the volume level went quiet again. My guess is something could be shorting slightly? Out of curiosity though is the printed circuit board in the desktop 746 the same as in the 741? as I would just do a straight swap over. I got a ivory 746 the same day as getting this. I hope someone can help Thanks Ryan

28th Aug 2014, 8:28 am	#2
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,864	Re: 741 Wall phone short circuit issue? I'm sure you're right, but could also be a crack in the PCB, a dry joint on one of its connections, one of the wires adrift on the ASTIC (transformer), the board being shorted out by the metal base and so on. Another thing to check is that the dial contacts that short-out the receiver (earpiece) are OPEN when the dial is at rest. And yes, you could swap the PCB to narrow down the fault if you wished. Nick.

28th Aug 2014, 6:16 pm	#3
Ryan_1993 Hexode Join Date: Sep 2012 Location: Yorkshire, UK. Posts: 329	Re: 741 Wall phone short circuit issue? bit of an update I swapped out the circuit board and all seems fine, no idea what the issue was, but I guess something wasn't quite right with the board that was in it originally.

28th Aug 2014, 7:36 pm	#4
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,130	Re: 741 Wall phone short circuit issue? Have you tried reassembling the 746 with the circuit from the 741? If so, has the fault now migrated to the 746? If the answer is yes, then there is indeed a fault in the circuit board. Tracking it down wil be the next challenge. If no, there was presumably a dodgy connection that has been been cured during the swap over by removing one set of connections and making the other. __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)