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Old 6th Apr 2019, 5:13 pm   #21
Simon Gittins
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Default Re: Ferguson 382U Firefly not playing ball

The idea about the 220pF capacitior was always a long shot, best to continue logical fault finding.

Is the V3 anode voltage stable now? If the variation is repeatable it's worth checking R14.
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Old 6th Apr 2019, 5:35 pm   #22
PJL
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Default Re: Ferguson 382U Firefly not playing ball

Other than the odd 100V, the DC conditions on V3 look good, the screen grid current is directly related to the anode current so the correct voltage on the screen grid indicates it is conducting OK.

Set to MW again, check the V2 screen(1) but I suspect it will be OK.

At this point it would be a good idea to check your capacitor replacements were done correctly. You said you replaced C16 but I suspect you meant C17?

It's also worth checking all wavebands to see if anything is happening as it might help narrow down the fault.

Touch each grid with your meter probe with the other probe disconnected (be careful). starting at V5 and working backwards. Using your meter as an aerial should pick up some noise so I would expect a click or even hiss.

Last edited by PJL; 6th Apr 2019 at 5:44 pm.
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Old 8th Apr 2019, 10:50 am   #23
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Hi thanks for suggestions,

V2 Screen = 138V

However discovered what I believe to be "R11" (3k3) was in fact measuring 17.7k - replaced, although no apparent effect.

Pete
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Old 8th Apr 2019, 11:39 am   #24
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

R14 actually seemed O/C, so added a 4k7 ( nearest value I had ) in parallel and now THAT also seems O/C when in situ

Disconnected the 4k7 and pulled one leg of the original 3k3, now R14 reads around 4k..?

I have no idea...

Pete
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Old 8th Apr 2019, 12:34 pm   #25
Boater Sam
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Default Re: Ferguson 382U Firefly not playing ball

Erroneous meter readings,,,,,, Check the meter against a known voltage, inspect leads for breaks.

O/C or S/C? infinite ohms or zero ohms?

Last edited by Boater Sam; 8th Apr 2019 at 12:35 pm. Reason: added
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Old 8th Apr 2019, 1:08 pm   #26
PJL
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Default Re: Ferguson 382U Firefly not playing ball

R14 is V3 anode feed resistor and you have already noted that the anode voltage dropped to 100V at one point. Check for poor connections.

I would like to go back to your capacitor replacement list as you appear to have missed some:
* C16 is marked as replaced but it is only 33pF (ceramic or mica) and unlikely to have failed.
* C36 (V3 screen decoupling) and C37 (V3 anode decoupling) should be replaced as both have quite high voltages across them and loss of capacitance will impact gain.
* C50 (audio decoupling capacitor) not critical but it is probably paper.
* C52 (output audio coupling capacitor) this is 'that' capacitor and should be the first you replace as failure will cause the output valve to conduct heavily with possible damage to the output transformer.

Not sure what type these capacitors are in this set so they may be OK? Would help us if you posted a picture of the underside.
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Old 8th Apr 2019, 3:10 pm   #27
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Thanks PJL!

Okay, after now finding the actual Ferguson Service Manual from "***********************"
I can now understand the circuit diagram with greater clarity!

Correction: R11 was in fact R7 and perfectly fine.! R14 is in fact s/c ( this is what the wavechange switch does, when set to MW (doh!)

C52 was in fact disconnected at one leg, component now replaced.

will now look at replacing C36,C37 and C50

Pete
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Old 8th Apr 2019, 3:22 pm   #28
PJL
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Default Re: Ferguson 382U Firefly not playing ball

My references all relate to the circuit in trader 1299. If C52 in the trader was disconnected it is not surprising that it was not working as this feeds the audio to the output valve.
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Old 8th Apr 2019, 4:22 pm   #29
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Hi,

C36 and C37 and C50 now replaced.
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Old 8th Apr 2019, 5:13 pm   #30
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Just to confirm a sig generator on to the grid of V4 gives a nice loud output.

Pete
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Old 8th Apr 2019, 5:53 pm   #31
PJL
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Default Re: Ferguson 382U Firefly not playing ball

Do you still not have any reception on any waveband? If not can you check your capacitor replacement carefully.

As DC measurements look OK and your audio stages work, it looks like an RF problem. My only reservation is that FM and AM use separate signal paths so finding the fault may be tricky. I guess you do not have an RF signal generator?
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Old 8th Apr 2019, 7:09 pm   #32
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Hi PJL, no unfortunately I don't. I have a a 20Mhz (allegedly) DSO which has a built in sig generator - but only to 20Khz.

I'll go check each cap that hasn't been replaced - although if I could eliminate everything in that shielded RF can, that would be a bonus, or do you reckon its worth dismantling it just in case?

thanks, Pete
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Old 8th Apr 2019, 9:48 pm   #33
PJL
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Default Re: Ferguson 382U Firefly not playing ball

It was checking your wiring of the capacitors that you have replaced that I had in mind. It is easy to wire one to a wrong pin and kill the RF signal.
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Old 8th Apr 2019, 10:06 pm   #34
Mike. Watterson
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Default Re: Ferguson 382U Firefly not playing ball

Ah, so taking into account sampling, two channels etc, it's equivalent to a 500 KHz analogue scope that can display a square wave!

You can use another radio as a signal gen. Put about 5 turns of wire around a small transistor set to pick up its L.O. It will be 455KHz off the dial frequency.
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Old 8th Apr 2019, 10:25 pm   #35
Simon Gittins
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Default Re: Ferguson 382U Firefly not playing ball

Quote:
Originally Posted by el gringo View Post
if I could eliminate everything in that shielded RF can, that would be a bonus, or do you reckon its worth dismantling it just in case?

I wouldn't recommend that. Once you open the can, you will upset the alignment to some extent. In my case all those years ago, I used a signal generator to prove the fault to the IF stage, confirmed all voltages were correct and then established that one winding wouldn't tune so I knew that it had to be a faulty capacitor in the can.


Checking your previous work and using another radio to help prove the fault to one particular stage sounds like the best plan.
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Old 9th Apr 2019, 9:46 am   #36
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Default Re: Ferguson 382U Firefly not playing ball

Reading your replies,It is very simple when replacing a component to connect to the wrong point we have all done it, it would help if you could download some pictures of the radio and work carried out, as it is possible someone may spot your problem, you can go round and round in circles and still miss something.
The worst fault to find is man made.
John
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Old 10th Apr 2019, 3:41 pm   #37
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Here's the now very scrappy looking set

( will of course be tidied up, once I can get it working )
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Old 10th Apr 2019, 3:47 pm   #38
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Quote:
Originally Posted by Mike. Watterson View Post
You can use another radio as a signal gen. Put about 5 turns of wire around a small transistor set to pick up its L.O. It will be 455KHz off the dial frequency.
Hi Mike - I've given that a try, with the "sig gen" radio on MW and trying the grids of the RF section (inc the detector stage). The only thing I get is light clicking induced in to my "sig gen" radio speaker?

thanks, Pete
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Old 10th Apr 2019, 4:27 pm   #39
PJL
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Default Re: Ferguson 382U Firefly not playing ball

Can you do a couple more pictures as the resolution is not quite good enough. Maybe two pictures one of each end of the chassis would work. There are still a few wax capacitors in the set?
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Old 10th Apr 2019, 6:34 pm   #40
el gringo
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Default Re: Ferguson 382U Firefly not playing ball

Hope these are a little clearer..

There are only two Wax ones left, however they're not grounded

thanks, Pete
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