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Old 30th Sep 2017, 6:32 pm   #1
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Default BBC AC test meter ATM/1/257

I have had one of these units for over 25 years & it has performed faultlessly.

Then, just as I needed to use it (things always develop a fault then!) the internal calibration & also the left-hand meter, is reading incorrectly.(not the PPM, which is reading correctly).

Does anyone have a circuit diagram for this unit, as annoyingly, unlike its partner the TS10P/341, which I also have, there's no circuit diagram in the lid.
The lid went missing some years ago & I had to fabricate another.

Any help would be much appreciated.

Dave.
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Old 30th Sep 2017, 7:42 pm   #2
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Default Re: BBC AC test meter ATM/1/257

There's the ATM1 on the ECO pages of bbceng.inf if it's any good. If it's not there I'll look in our BBC ECO books which we still have kicking about at Skelton.

http://www.bbceng.info/ti/eqpt/ATM_1.pdf
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Old 1st Oct 2017, 12:46 pm   #3
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Default Re: BBC AC test meter ATM/1/257

Thanks Russell,

Really appreciated, that should help me sort out the problem.

Just checked it against my Lindos, and the valve voltmeter part of the ATM/1 more or less consistently reads 5 dB low, so it should be fairly easy to find.


Thanks again,

David.
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Old 1st Oct 2017, 6:31 pm   #4
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Default Re: BBC AC test meter ATM/1/257

All done, several very leaky capacitors, & resistors that had gone virtually o/c - and it's as good as new. Within 0.1dB on most of its ranges.

I'll have to look at the TS10/341 next as the oscillator on that isn't as pure as it might be!
Is there a full description/ circuit available for that on the bbceng info site?
I wasn't able to locate it, but it would be useful, as the only circuit of that I have is in its lid, & that's fairly illegible, having gone completely yellow.

Thanks again Russell.

David.
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Old 1st Oct 2017, 9:05 pm   #5
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Default Re: BBC AC test meter ATM/1/257

There's the ACO info (I called it ECO, sorry... ) for the TS10 tone source here, David.

http://www.bbceng.info/ti/eqpt/TS_10.pdf

The Apparatus in Code Order list is buried amongst the 'Technical Instructions' tab
under 'quick links', here. Well worth a read!

http://www.bbceng.info/ti/ti_top.htm
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Old 2nd Oct 2017, 9:49 am   #6
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Default Re: BBC AC test meter ATM/1/257

Absolutely wonderful,

Thanks for that Russell, really appreciated. I hadn't realised so much had been scanned & archived.

Have just used the ATM/1 to set up a compressor limiter I needed to use in order to make a CD of a friend's wedding.

I could have of course used the Lindos LA101, but then that's in my workshop, underneath a load of other test kit on the shelf above my bench.
Well that's my excuse,- I actually prefer the analogue meters on the ATM/1 for 'live' applications.

Thanks again, I can now sort out the TS10, which I need to use, as my Lindos LA102 has now developed a strange fault! It must be 'audio equipment fault month'...

David.
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Old 2nd Oct 2017, 1:31 pm   #7
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Default Re: BBC AC test meter ATM/1/257

David,

Glad you got sorted. We still have three ME2 / 4A sets kicking about: the 'economy' version of the EP14 Wien-Bridged-based a.c. test sets, as well as a pair of Lindos units (Lindii?). Handy to have around although greatly underused except perhaps for homers (foreigners)*. The last time I used a valve a.c. test-set was the old 'sound-dalek' at Kirk o' Shotts back in the '80s.

Best thing we had a was a Neutrik set, but the TV and domestic radio lot (Crown Castle, later NGW, now Arqiva) got that when we divvied up the equipment upon break-up of BBC Transmission.

What's the matter with your Lindos?

* See other thread.
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Old 4th Oct 2017, 1:17 pm   #8
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Default Re: BBC AC test meter ATM/1/257

Thanks Russell,

After having used the ATM/1 in earnest as it were, I discovered some negative drift on the PPM 'zero-set', to the point where I couldn't get the needle back on to zero. So, out of the case it came again, & I replaced a number of resistors in the meter driver stage with modern close-tolerance types. This fixed the final fault, & I left it on for a day, with negligible drift. Used it last night in PPM mode to monitor the audio I was transferring to CD. Worked a treat, very nostalgic PPM! Very satisfying in the glow of firelight, with a glass of red wine in the other hand!

In total I replaced 13 resistors & 5 capacitors, - none of them 'blanket-changed' they were all causing various symptoms. The capacitors, mostly the TCC metal can types were exceedingly leaky. Interestingly, none of the electrolytics have failed. I was certain that one of the cathode bypass caps would be dodgy, but it wasn't. Absolutely perfect both capacity-wise, and with an ESR that puts some modern caps to shame.

I'm now enthusiastic to do the same with the TS10, just for fun, as I doubt that I'd use it for serious applications.

Interesting that you mention the Neutrik, I had one of those back in the 80's I really liked that, very intuitive, and a decent analogue meter. I also have here a Ferrograph RTS-2 & the aux unit (adds balancing, for real audio!) that I used to use before I got the Lindos. Still use it occasionally for testing mics etc, as it has it's own low-power amplifier. Sadly the meter has seen too much UV, and the red markings for 'set, and 0dB' have all but faded away. Could do with a new meter, as the needle is bent, although I can probably fix that, having just repaired an 'Unrepairable' (according to Canford) Ernest Turner PPM, where the needle had actually broken off.

The Lindos, or Lindii, it is a pair, - it's the LA102 that has the major problem. It is an intermittent fault, but on power up, the LCD display goes crazy, & starts pulsing. It may then settle down, but in mid-use it can start jumping out of the selected mode & do its own thing, then revert back to a black screen.

I keep thinking of sending it back to Lindos for the latest upgrade, I thought about it two years ago, but now the price has gone up considerably!

The problem is being retired, I can't really justify the cost, as I probably won't use it enough on 'paying jobs' to get my money back. However, 'The Boss', - my wife thinks I should do it or bin it, which I'm certainly not going to do! If I do get the upgrade, I'd rather like to go for the PC 'Win for Lin' software, but that's also not cheap.

Sorry, gone a little 'off- thread' here, but it is all allied.

Regards,
David.
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Old 6th Oct 2017, 6:25 pm   #9
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Default Re: BBC AC test meter ATM/1/257

Re-seating all the socketed ICs on the logic PCB usually helps. The analogue board is not immune either. Having a look at the PSU is worthwhile too...

We still use the Neutrik TP401 for teaching - nothing else has such an intuitive user interface. We'd love to have one or two more, but they are very rare. Other test sets have lower noise floors or deeper distortion filters, but are pigs to drive by comparison. We have the replacement - the A2D - and that's a horror in the UI department, which is a shame as we would have bought a couple more to replace the TP401s if they'd been any good. Now discontinued, but these days we don't have any budget anyway
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Old 14th Oct 2017, 10:43 am   #10
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Default Re: BBC AC test meter ATM/1/257

Thanks for that.

Haven't been on the forum for a few days, -restoring a Philips 17" TV, so missed your very informative reply.

I will have a look at the IC sockets as suggested. Also I have had PSU problems with the Lindos before, so will also look in that area.

All agreed re the TP401, a great piece of kit, very easy to use.


David.
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