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Old 8th Oct 2018, 4:29 pm   #21
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Default Re: G & E Bradley CT-471

I think you need to edit your post while you still have time.

AF124 will replace OC170.
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Old 8th Oct 2018, 5:03 pm   #22
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Default Re: G & E Bradley CT-471

I see I put 117 instead of 170! Ran out of time to edit.

I see the AF124 is available as new old stock only, but quite expensive. I'm wondering if a cheaper silicon would work?
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Old 8th Oct 2018, 8:34 pm   #23
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Default Re: G & E Bradley CT-471

All the OC170 transistors check out fine, the issue is with high ESR and leaky caps, the biggest issue though is having the calibration prodedure and voltages etc. though, as the manual I have is for the BJT version not the FET!
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Old 8th Oct 2018, 8:37 pm   #24
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Default Re: G & E Bradley CT-471

As an aside i was in Birketts Lincoln last week, he had bags of NOS AF115 transistors with I would say maybe 50/60 per bag at 1 each.
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Old 8th Oct 2018, 8:45 pm   #25
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Default Re: G & E Bradley CT-471

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Originally Posted by m3vuv51 View Post
All the OC170 transistors check out fine, the issue is with high ESR and leaky caps, the biggest issue though is having the calibration prodedure and voltages etc. though, as the manual I have is for the BJT version not the FET!
I need to get checking my caps.

What I might do is replace the biasing resistor with a trim pot so that I can use silicon transistors as some of mine are shorted, so will need replacing. Then when happy, I'll replace the trim pots with fixed value resistors.

Once up an running, maybe we can go through the calibration together. I'm sure some how we'll work it out.

I've not actually looked in the manual I have, it is one for the C version which my meter is, so hopefully there's something in there.
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Old 9th Oct 2018, 11:03 am   #26
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Default Re: G & E Bradley CT-471

Some research on here and other areas of the internet suggests that apart from the OC170 transistors, there shall be no other transistors in this meter which suffers from tin whisker.

Is that correct?
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Old 9th Oct 2018, 1:59 pm   #27
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Default Re: G & E Bradley CT-471

Can't speak for other, but all my transistors, seem fine. Only issue I had was the 2.5V rail wouldn't go below 2.7V. Had to change some resistors that had gone off spec, most of the caps were leaky with high ESR though, apart from the mustards etc.

Cheers, Paul M3VUV.
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Old 9th Oct 2018, 2:48 pm   #28
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Default Re: G & E Bradley CT-471

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Does anyone have a PDF (or something downloadable) manual for the G & E Bradley CT-471?
Just to answer the original question........there's a perfectly good manual I did yonks ago in PDF on the vmarsmanuals site: http://www.vmarsmanuals.co.uk/archiv...Multimeter.pdf

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Old 9th Oct 2018, 3:54 pm   #29
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Default Re: G & E Bradley CT-471

Bill_wme did send me a manual a while ago, but thanks for the link.
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Old 15th Oct 2018, 2:25 pm   #30
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Default Re: G & E Bradley CT-471

Well I've got one of these sort of working, but on most scales the meter needle swings about all over the place, sort of oscillates at random, it's steady on the batt check position though. I've tried tapping and wriggling everything in sight to try to look for a dry joint and cleaned the switch contacts.

Any ideas where to look?

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Old 15th Oct 2018, 2:49 pm   #31
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Default Re: G & E Bradley CT-471

That's what mine does. I know you said the transistors are OK, but I'd suggest testing those again.

I've got some transistors to fit, then see what happens.
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Old 15th Oct 2018, 9:49 pm   #32
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Default Re: G & E Bradley CT-471

OK, well the transistors (AF178) I bought are no good. They all test OK on a DMM but the Peak DCA55 tests them as all having shunts between base and emitter with widely varying Hfe.
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Old 15th Oct 2018, 10:28 pm   #33
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Default Re: G & E Bradley CT-471

started looking at it againe tonight but my soldering iron heater went o/c,new one ordered,keep me posted,cheers paul m3vuv.
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Old 16th Oct 2018, 1:38 pm   #34
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Default Re: G & E Bradley CT-471

Some research and what's in the DCA55 manual suggests that maybe the shunt between base and emitter may be quite normal.

So I thought we'll have a go. I've replaced the three OC170s with AF178s, but the meter still behaves in the same way.

Back to the drawing board.
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Old 16th Oct 2018, 9:18 pm   #35
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Default Re: G & E Bradley CT-471

So some more testing tonight, to recap, meter appears to work on battery check fine, but any other function isn't performing with needle sitting somewhere on the scale but nothing else happening.

As I'm working on the amplifier board, I'll remove that entirely and test the board completely. Until I understand the theory of operation, that's the best I can do at the moment.
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Old 16th Oct 2018, 9:49 pm   #36
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Default Re: G & E Bradley CT-471

I looks as though there may be some 'Hunts' capacitors with bulged ends.
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Old 16th Oct 2018, 10:37 pm   #37
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Default Re: G & E Bradley CT-471

does your meter needle swing all over the place as well?
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Old 16th Oct 2018, 10:43 pm   #38
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Default Re: G & E Bradley CT-471

Sometimes, not as bad as it used to, but the needle just sort of sits at a point, sometimes goes far left.
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Old 16th Oct 2018, 11:16 pm   #39
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Default Re: G & E Bradley CT-471

At this point I'm not sure where to go next, as I'm never sure which drawing is the correct one, another set I have the schematics aren't fitting the page. I need to find something which explains how it works, what does what, or I'll literally have to remove every component testing each one at a time.
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Old 17th Oct 2018, 11:38 am   #40
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Default Re: G & E Bradley CT-471

There's a few things here which I could try

https://www.radios-tv.co.uk/communit...1c-multimeter/

third from last post gives me something which I could try.
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