Stuck on a BRC 1400! - UK Vintage Radio Repair and Restoration Discussion Forum

Focus Diode · 7th Sep 2018, 5:54 pm

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.

toshiba tony · 7th Sep 2018, 6:15 pm

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.

DangerMan · 7th Sep 2018, 6:16 pm

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

Pete

Freya · 7th Sep 2018, 6:44 pm

If the heater rectifier is shot then the valve heaters will be much brighter, not sure it would blow the fuse though.

Sideband · 7th Sep 2018, 7:01 pm

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?

Focus Diode · 7th Sep 2018, 7:11 pm

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.

Philips210 · 7th Sep 2018, 7:11 pm

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.

Regards
Symon.

Focus Diode · 7th Sep 2018, 7:24 pm

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

Brian

DangerMan · 7th Sep 2018, 7:30 pm

True but if the HT rectifier is short and the heater rectifier gets swapped by mistake, the fuse will still blow.

Focus Diode · 7th Sep 2018, 7:37 pm

It was definitely W11, the HT rectifier I replaced using a beefy BY127.

MickMcmichael · 7th Sep 2018, 7:55 pm

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

The system soleniod was was the culprit.

Focus Diode · 7th Sep 2018, 8:50 pm

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

Ed_Dinning · 7th Sep 2018, 9:15 pm

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.

Ed

Focus Diode · 8th Sep 2018, 9:06 am

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

Welsh Anorak · 8th Sep 2018, 10:37 am

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.

Focus Diode · 8th Sep 2018, 1:07 pm

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.

Focus Diode · 8th Sep 2018, 3:41 pm

Responded well to a clean up.
Need to find knobs for it.

Heatercathodeshort · 9th Sep 2018, 8:18 am

I've been following this with interest. So what caused the violent fuse blowing? John.

Focus Diode · 9th Sep 2018, 10:05 am

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

Focus Diode · 9th Sep 2018, 12:25 pm

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

7th Sep 2018, 5:54 pm	#1
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	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. Attached Thumbnails

7th Sep 2018, 6:15 pm	#2
toshiba tony Heptode Join Date: May 2006 Location: Accrington, Lancashire, UK. Posts: 978	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.

7th Sep 2018, 6:16 pm	#3
DangerMan Heptode Join Date: Jul 2009 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 719	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

7th Sep 2018, 6:44 pm	#4
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	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. __________________ Stephen _________"It`s only an old telly" ___

7th Sep 2018, 7:01 pm	#5
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,572	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? __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

7th Sep 2018, 7:11 pm	#6
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	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.

7th Sep 2018, 7:11 pm	#7
Philips210 Nonode Join Date: May 2007 Location: Redruth, Cornwall, UK. Posts: 2,573	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. Regards Symon.

7th Sep 2018, 7:24 pm	#8
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: Stuck on a BRC 1400! Excellent suggestion Symon. I'll try that when I get back to the set tomorrow. Brian

7th Sep 2018, 7:30 pm	#9
DangerMan Heptode Join Date: Jul 2009 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 719	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.

7th Sep 2018, 7:37 pm	#10
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: Stuck on a BRC 1400! It was definitely W11, the HT rectifier I replaced using a beefy BY127.

7th Sep 2018, 7:55 pm	#11
MickMcmichael Pentode Join Date: Mar 2009 Location: Peterborough, Cambridgeshire, UK. Posts: 196	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.

7th Sep 2018, 8:50 pm	#12
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	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

7th Sep 2018, 9:15 pm	#13
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	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. Ed

8th Sep 2018, 9:06 am	#14
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	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

8th Sep 2018, 10:37 am	#15
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	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. __________________ Glyn www.gdelectronics.wales

8th Sep 2018, 1:07 pm	#16
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	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. Attached Thumbnails Last edited by Focus Diode; 8th Sep 2018 at 1:28 pm.

8th Sep 2018, 3:41 pm	#17
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: Stuck on a BRC 1400! Responded well to a clean up. Need to find knobs for it. Attached Thumbnails

9th Sep 2018, 8:18 am	#18
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Stuck on a BRC 1400! I've been following this with interest. So what caused the violent fuse blowing? John.

9th Sep 2018, 10:05 am	#19
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	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

9th Sep 2018, 12:25 pm	#20
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	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 Attached Thumbnails Last edited by Focus Diode; 9th Sep 2018 at 12:40 pm.