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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 28th Oct 2018, 11:28 am   #61
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Default Re: G & E Bradley CT-471

Power supply seems ok. 12v cal check is working.
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Old 28th Oct 2018, 5:38 pm   #62
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Default Re: G & E Bradley CT-471

So, what's happening now and I don't know why, as I have no idea how these things work is....

on DC current, on the 0.4 range I get meter movement, but the reading doesn't correleate at all with what I'm sending it.

The same on DC volts, on the 0.4 and 1.2 range.

So I need to work out why that is and why still nothing on any other range.

Though if I go to AC, the needle moves around to the centre and floats about a little.
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Old 28th Oct 2018, 8:31 pm   #63
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Default Re: G & E Bradley CT-471

Although it's not really working at all, I thought I'd have a go at the setting up/calibration process, to see what voltages I measure.

Going through the manual I have, which may not strictly be for the C version, if there is a difference in this part, I observe the following...

from page 42 of the PDF,

Quote:
Connect the test meter to the collector of VT18. The meter should read 5V +- 0.1V; note the reading. Set the function switch to V-AC. Adjust RV12 until the test meter reads 5.25V +-0.1V.
I was reading around -2v and when on AC couldn't adjust the voltage above 3.8V. If I adjust RV13 again, I can achieve the 5.25 and 5V, but that brings the collector voltage of VT13 up from a measured 13.78V to 15.66V.
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Old 28th Oct 2018, 11:48 pm   #64
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Default Re: G & E Bradley CT-471

So apart from that, todays progress is showing more activity from the meter, still have a long way to go though.

In the absence of a troubleshooting/fault finding guide with test points, all I can go on at the moment is the calibration/set up procedure.

It may be due to differences between the CT471 and CT471-C but I couldn't find tonight R80, to perform the test where I need to short R79 and R80 to earth to make checks to the chopper circuit.

In paragraph 5.6.4, the DC overall gain checks, RV1 adjustment was making no difference at all.

So those two areas are in need of some investigation.
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Old 2nd Nov 2018, 5:19 pm   #65
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Default Re: G & E Bradley CT-471

Can I confirm that these meters have a 1mA FSD movenemt?
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Old 2nd Nov 2018, 5:30 pm   #66
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Default Re: G & E Bradley CT-471

According to the cct diagram, yes.
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Old 2nd Nov 2018, 7:31 pm   #67
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Default Re: G & E Bradley CT-471

Thanks.

I'm getting somewhere.

Just going again through the set up procedure.

I find adjusting RV1 is making no difference, I've put a different pot in for now as the pot was stuck at 2.5k and wouldn't adjust to anything else, but still nothing. I've got to leave it now for the evening but I'm wondering what else could be causing no adjustment to the set up.

RV1 should be adjusted to set the meter to read FSD on VDC, 0.04v range with 40mV supplied.
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Old 3rd Nov 2018, 7:41 pm   #68
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Default Re: G & E Bradley CT-471

hi i had the same issue on one of these found it was resistors gone high in value around that part of the board,been a ew weeks so cant remember exactly what i changed. m3vuv.
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Old 3rd Nov 2018, 9:01 pm   #69
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Default Re: G & E Bradley CT-471

I haven't my notes in front of me right now but I do remember one of the CT471 meters I repaired had a duff pot: one of those with a bakelite top that carries the wiper and having the three hollow connecting posts.
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Old 4th Nov 2018, 2:42 am   #70
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Default Re: G & E Bradley CT-471

If you need any parts give me a toot as I've five of these. As long as I get one going the rest are surplus to my needs.
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Old 4th Nov 2018, 2:02 pm   #71
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Default Re: G & E Bradley CT-471

I may be interested in taking them off your hands to give me some future projects.
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Old 4th Nov 2018, 6:21 pm   #72
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Default Re: G & E Bradley CT-471

Have you sorted yours yet? They are a good source of hardware. I used one case for an ESR meter and the case and lid from another for a waterproof battery box for my eBike. I've just built an Atmel 328 based transistor/ESR/lc meter, so I'm going to check all the transistors for gain, leakage etc with that and see if I can nail it.

Cheers M3VUV.
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Old 4th Nov 2018, 10:17 pm   #73
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Default Re: G & E Bradley CT-471

I was thinking of fixing them up and getting them working.
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Old 8th Nov 2018, 11:23 pm   #74
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Default Re: G & E Bradley CT-471

Those with a working one of these, would it be at all possible to find out and let me know what value yours has RV1 and RV17 set to? This may help me pin point another issue.

Thanks.
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Old 9th Nov 2018, 1:22 am   #75
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Default Re: G & E Bradley CT-471

A 'C' ? I can do tomorrow for you. Pleae let me know any voltage measurements etc you may need before I close it up again.

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Old 9th Nov 2018, 2:26 pm   #76
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Default Re: G & E Bradley CT-471

These are from my 'C' version Mod state 11 (don't ask, I don't know!). All measurements taken on a precision Aneng 8008.

RV17 pins are terribly difficult to get to properly, I measured from either end of the resistance track to the wiper pin and got 460R and 670R. Very hard to be precise as you're trying to measure as close to the very end of the track as possible which is hidden by the rotating sections. No value given for this part in the manual.

RV1 I measured 1059K one end, 672R the other side, per the parts list it's meant to be a 2.5K pot so...maybe it's a 2K pot.

You have your 12V Cal voltage, 20V at the top of R70, 2.5V at the + end of C2?

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Old 9th Nov 2018, 10:48 pm   #77
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Default Re: G & E Bradley CT-471

Thanks Andrew.

I have the 12v cal voltage, I did check the 20v rails and 2.5v, but I'll check again and make a note of it's presence at R70 and C2.

I am getting closer as I'm now at a stage where the meter is responsive, where as before it wasn't. I just need to sort out why it's reading incorrect. It could be as has been pointed out, some out of spec resistors.
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Old 12th Nov 2018, 11:44 pm   #78
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Default Re: G & E Bradley CT-471

I've just noticed on the attenuator board, R10 is missing! How I didn't spot this before, I don't know. But the affect on the meter is unknown at the moment, unless it's the current issue I have.

Drawings state the value of R10 is to be set on test. So no actual value given.

If you're able to take another peek, what's the value of your R10?

Thanks.
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Old 13th Nov 2018, 1:48 am   #79
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Default Re: G & E Bradley CT-471

Just checked those voltages again, all are fine. Went throught most of the resistors I could get to on the attenuator board, which tested fine. Back to the drawings to try and work out what is going on.
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Old 13th Nov 2018, 11:58 pm   #80
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Default Re: G & E Bradley CT-471

With regards to the rotary switches, such as rainge, function etc, is there some form of diagram which details each connection with information?

On the drawings, it's shows for example, SA is the range switch, but the drawings have SA1, SA3 and so on, but with no explanation to what each position actually is.

It would save me a lot of time if there was this information on the drawings to try and trace through each range.
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