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Old 7th Sep 2018, 5:54 pm   #1
Focus Diode
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Default Stuck on a BRC 1400!

Never thought I could get stuck with one of these sets.

This Ferguson 3645 16" model which landed today was found to have a blown 1.5A mains fuse. Simple I thought, probably a shorted mains filter capacitor or HT rectifier.

Initially I thought the HT rectifier was s/c. Not so as it measured fine when removed. Re-fit it, snip the mains filter. Fuse blows instantly!

Replace the HT rectifier just incase. Same thing happens.

The protection capacitor across the rectifier is ok.

Any ideas? It's of course impossible to make voltage readings with the fuse blowing instantly.
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Old 7th Sep 2018, 6:15 pm   #2
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Default Re: Stuck on a BRC 1400!

I've seen loads of your posts, you are the whizz kid on tv's. Nothing measurable cold? Haven't got the manual to hand but these were the most basic on the mains input side. I'll be watching with interest.
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Old 7th Sep 2018, 6:16 pm   #3
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Default Re: Stuck on a BRC 1400!

Don't forget there's a heater rectifier (W10) as well as a HT one (W11).... you did change the correct one... ?

Pete
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Old 7th Sep 2018, 6:44 pm   #4
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Default Re: Stuck on a BRC 1400!

If the heater rectifier is shot then the valve heaters will be much brighter, not sure it would blow the fuse though.
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Old 7th Sep 2018, 7:01 pm   #5
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Default Re: Stuck on a BRC 1400!

I don't know the 1400 but check the simple things first, the switch (may have an internal short), are there any VDR's in the mains circuit? Is the smoothing cap short circuit? Has someone 'been in there' and done something stupid?
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Old 7th Sep 2018, 7:11 pm   #6
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Default Re: Stuck on a BRC 1400!

Hi there, thanks for your contribution.
No evidence of "Unauthorised" service work.
The switch is OK. Cold checks so far haven't revealed any shorts. Clearly when mains is applied something objects as the mains fuse blows immediately.

I now suspect the main smoothing block. I'll try fitting the NOS replacement when I find it in due course.
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Old 7th Sep 2018, 7:11 pm   #7
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Default Re: Stuck on a BRC 1400!

Hi

Looking at the circuit diagram, I'd first disconnect one end of W11, the HT rectifier to isolate HT rails HT1, HT2 and HT3. That should eliminate a substantial amount of the set. If the fuse still blows then possibly there's a heater chain fault.

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Old 7th Sep 2018, 7:24 pm   #8
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Default Re: Stuck on a BRC 1400!

Excellent suggestion Symon. I'll try that when I get back to the set tomorrow.

Brian
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Old 7th Sep 2018, 7:30 pm   #9
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Default Re: Stuck on a BRC 1400!

True but if the HT rectifier is short and the heater rectifier gets swapped by mistake, the fuse will still blow.
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Old 7th Sep 2018, 7:37 pm   #10
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Default Re: Stuck on a BRC 1400!

It was definitely W11, the HT rectifier I replaced using a beefy BY127.
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Old 7th Sep 2018, 7:55 pm   #11
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Default Re: Stuck on a BRC 1400!

I once got caught out with a similar problem on a Thorn 950.

The system soleniod was was the culprit.
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Old 7th Sep 2018, 8:50 pm   #12
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Default Re: Stuck on a BRC 1400!

Interesting. The fusible resistors are both intact on this set.

Something to look at if the mains fuse continues to blow with the HT rectifier disconnected.

I'll report back tomorrow. Thank you all for your help and contributions.

Brian
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Old 7th Sep 2018, 9:15 pm   #13
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Default Re: Stuck on a BRC 1400!

Hi, how about the good old lamp limiter or variac. That should allow you to get voltage readings without fuses blowing and hopefully trace where the amps are going.

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Old 8th Sep 2018, 9:06 am   #14
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Default Re: Stuck on a BRC 1400!

Of course you're right Ed. Will have to dig mine out. Thought being a simple 1400 I'd just plug it in having made the usual cold checks.

Not a good idea as it turned out.

The set was found to have a blown mains fuse. It's uncertain if the set failed in use many years ago or if someone tried it more recently. The person I got it from didn't test it.

So I'll be getting the lamp limiter down later and will look for the multicap while I'm at it.

Cheers,
Brian
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Old 8th Sep 2018, 10:37 am   #15
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Default Re: Stuck on a BRC 1400!

Disconnecting the HT south of the rectifier is good advice. I'd also disconnect the solenoid as that can do unusual things.
That's a nice early one you've got there.
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Old 8th Sep 2018, 1:07 pm   #16
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Default Re: Stuck on a BRC 1400!

After more tests as suggested above we have first light! Well, actually the second as the very first gave frame collapse due to the PCL805 being bent out of position. Another none original of the unbranded type I note.

The dropper was found to have two o/c sections so was replaced. The mains fuse no longer blew when tried with a lamp limiter. I guess it needed a gentle wake up.

This was the result. S/C W10? I'll replace that next.

Edit- Turned out to be innocent but I'm happier a BY126 has been fitted on the PCB side.

So, there's no frame lock nor proper line lock. Obviously many components will need replacing which will be attended to in due course.
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Old 8th Sep 2018, 3:41 pm   #17
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Default Re: Stuck on a BRC 1400!

Responded well to a clean up.
Need to find knobs for it.
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Old 9th Sep 2018, 8:18 am   #18
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Default Re: Stuck on a BRC 1400!

I've been following this with interest. So what caused the violent fuse blowing? John.
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Old 9th Sep 2018, 10:05 am   #19
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Default Re: Stuck on a BRC 1400!

Hi John, I'm not completely sure. On making the tests yesterday I did disconnect the supply to the system switch solenoid, so it could be that.

I want to get the set functioning properly then I'll try reconnecting it.

Cheers,
Brian
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Old 9th Sep 2018, 12:25 pm   #20
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Default Re: Stuck on a BRC 1400!

Replacing R45 sorted out the none locking timebases. The line hold continues to drift while warming up which should respond to a new 30FL2.

Been able to assess the set further. The CRT isn't brilliant with some misalignment evident on test card. Performance on 625-lines seems OK. Last picture taken on 625.

Much work still to do.

Brian
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Last edited by Focus Diode; 9th Sep 2018 at 12:40 pm.
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