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Old 3rd Feb 2020, 11:08 am   #1
Rudolph
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Default London 8

Hi all

My London 8 has been hanging on the wall since 1989 giving excellent service with only the occasional bleat for a new battery, but it is now in need of a little TLC. The extension phones are not ringing as loudly as before and extension
22 (a Real Phone with a bell) just goes 'ping'.

The ringing volts off load are now down to 25, half of what I would have expected.

If anyone could offer some advice on this, maybe even a circuit diagram, I would be very grateful.

Rudolph
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Old 3rd Feb 2020, 4:20 pm   #2
AndiiT
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Default Re: London 8

Hi, It's doubtful that you will be able to obtain a circuit diagram for your London 8 as most PBX's of this kind were intended to be swapped out in the event of any obscure faults.
It may be worth checking and replacing any suspect electrolytic capacitors in the PBX though as they could be the cause of your problem depending on how the ringing current is obtained.

Regards

Andrew
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Old 4th Feb 2020, 3:05 pm   #3
Pellseinydd
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Default Re: London 8

I never managed to get a circuit diagram for one and I did the course on them at National Telephones. I used to maintain plenty of them. The problem was always the PSU in both the L8 and the L16. Another thing if you power it down, it is very likely that the small cell which retains the memory will need renewing as you'll probably find the memory has gone. You can still get ones on eBay. They were a great little PABX designed to use pulse dialling phones without a recall button normally used on electro-mechanical PABXs.

My very late version with 'multi-network routing' ( where different codes 91, 92 etc were dialled for BT, Mercury etc ) still hangs on the wall - must fire it up one day.

Ian J
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Old 5th Feb 2020, 1:48 am   #4
Graham G3ZVT
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Default Re: London 8

I've asked someone in the uk.telecom newsgroup who I know has a London 8 if she has any manuals, and she does have the user and installation manuals for the London 16. There won't be any proper schematics, they're never are unfortunately, but she will look if anything else is useful.

What might be an even better plan is if you could take detailed photographs of the boards, particularly the PSU area, maybe one of us might spot something.

Bear in mind if you do that, the normal Forum upload system seriously reduces definition, you can circumvent that by uploading them as ZIP files or linking to imgbb.com, Google photos, or other external site.
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Old 5th Feb 2020, 2:04 am   #5
Graham G3ZVT
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Default Re: London 8

I always associate London systems with seedy hotels, which is where many of them were installed when I worked for a particular firm based in Bury.

Oh, and often equipped with earth-start lines for some reason, guaranteed to confuse the inexperienced (like me).
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Old 5th Feb 2020, 10:31 am   #6
Pellseinydd
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Default Re: London 8

The L16 was the popular one as it was the smallest of the London range which had 'hotel' software that produced a ready produced 'invoice' with all the calls listed & costed for any extension by just plugging a printer in. No other system of its size at that time had that facility. They needed an external PC with program plus printer Hence the popularity of the L16. There wasn't an L8 version with 'hotel' software.

I think I may have mentioned it before but the London range was manufactured by LM Ericssons' factory up in the North East of England for National Telephones. Alcatel bought out National Telephones and produced a few London range L8/16's badged 'Alcatel' then stopped product. About then some of the guys from Ericssons set up near Scunthorpe to repair London range as they had all the circuit diagrams test kit etc. That was where I used to get complex main circuit boards fixed. They'd never part with the circuitry for obvious reasons. Not sure if they are still going but was in an industrial estate on the outskirts of Scunthorpe. Andy's suggestion of checking the capacitors is a good starting point.

When it comes to 'earth start' exchange lines - that was a system that BT PABXs tended to use so if new lines were fitted for a PABX they made the assumption unless you specifically asked fir 'loop start'.

I have the engineers' singe volume for the L8 which includes the User Guide, Installation and Programming manuals plus those for the rest of the London Range. Somewhere in the loft is a London 64 - an unusual version as it has 64 extensions plus the exchange lines. Normally the maximum number of both the exchange lines and extensions was that of the title i.e. a London 64 had a maximum of 56 extensions plus 4 or 8 exchange/tie lines.
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Old 10th Feb 2020, 11:57 am   #7
Rudolph
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Default Re: London 8

Thank you all for your thoughts and suggestions. As it is over 40 years old electrolytics were my first thought, and my second thought was what are electrolytics doing in a 50v 25Hz supply. How would you get the 25Hz supply?

The suspect electrolytics are shown in the pics and look ok at first glance apart from the couple of blobs of araldite to stop them moving around too much - getting them out could be a problem. Everything looks alright on the board but R70 and its neighbour and R59 are showing signs of a little overheating.

But 'swapped out', Andrew, I don't think I could explain to my good and faithful London8 that it is time to be 'swapped out'.

Regards
Rudolph
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