Fergi 3821 (1500 chassis) frame collapse - UK Vintage Radio Repair and Restoration Discussion Forum

tvden · 6th Oct 2006, 5:22 pm

I was given this set by a friend, no wonder!

After applying power I had sound OK but also frame collapse

With a signal applied there is a picture, a bit narrow though. Tried a few of the suggestions from my previous thread for a circuit, looks like the culprit is the frame output transformer which reads only 6 R instead of 8.2 R, also it must have run hot as there is a bit of wax residue on the underside.

Focus Diode · 6th Oct 2006, 9:40 pm

I presume a known good PCL805 has been fitted. Next check C79, output pentode cathode bypass capacitor (160uF) and resistor R103 (300ohms). Check the value of R103 anyway as a changed value resistor could shorten the life of the PCL805. Then C101 (100uF), R123 (330Kohm feed from boost line) and C89 (1uF).

As John says dry joints on the frame tx are common. Another possibility is a dry joint on the PCL805 valve base, or a faulty valveholder.

I've not known a frame tx to fail in these or the 1400 series, but there's always a first time. I should have a 1400 transformer somewhere which should be sutiable.

Cheers,
Brian

Steve_P · 6th Oct 2006, 10:26 pm

Check the height control - it's a skeleton pot on these and it does tend to go intermittent or die.

Cheers,

Steve P

tvden · 6th Oct 2006, 10:49 pm

Hi all
I will have another look at the set over the weekend re your suggestions, and see if I can find anything. I think it would be a good viewable set if I can expand the frame!

regards Den

Focus Diode · 7th Oct 2006, 12:07 am

Quote:

Originally Posted by Steve_P

Check the Height Control - it's a skeleton pot on these and it does tend to go intermittent or die.

Very true Steve, many thanks for pointing this out.

Cheers,
Brian

Welsh Anorak · 7th Oct 2006, 5:24 pm

Hi
Never had a tx go either - but they do go very waxy. Don't forget the TWO 330k (ish) resistors in series with the height pot as it's fed from the boost line - one's near the LOP stage and can be missed - aim for around 250v at the 'top' of the height pot.
lyn

dazzlevision · 7th Oct 2006, 7:10 pm

Hi,

There are two 18k 0.5W resistors in the frame linearity feedback circuit. They are unreliable in this chassis.

Regards,

Dazzlevision

Hybrid tellies · 7th Oct 2006, 9:30 pm

I agree with all that has been said. I seem to remember an electrolytic cap, abut 1uf just off the boost line on the feed to the height cct which use to play up. Sometimes it just dried up but occasionally it would go leaky or short circuit.
If you have a cct diagram and a meter the 1500 is one of the easiest chassis to fault find on.
Oh don't forget to keep the brightness turned down with frame collapse, this will avoid any risk of phosphor burn across the screen.

6th Oct 2006, 5:22 pm	#1
tvden Retired Dormant Member Join Date: Oct 2003 Location: Halesworth, Suffolk, UK. Posts: 413	Fergi 3821 (1500 chassis) frame collapse I was given this set by a friend, no wonder! After applying power I had sound OK but also frame collapse With a signal applied there is a picture, a bit narrow though. Tried a few of the suggestions from my previous thread for a circuit, looks like the culprit is the frame output transformer which reads only 6 R instead of 8.2 R, also it must have run hot as there is a bit of wax residue on the underside.

6th Oct 2006, 9:40 pm	#2
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: Fergi 3821/ 1500 chassis frame collapse I presume a known good PCL805 has been fitted. Next check C79, output pentode cathode bypass capacitor (160uF) and resistor R103 (300ohms). Check the value of R103 anyway as a changed value resistor could shorten the life of the PCL805. Then C101 (100uF), R123 (330Kohm feed from boost line) and C89 (1uF). As John says dry joints on the frame tx are common. Another possibility is a dry joint on the PCL805 valve base, or a faulty valveholder. I've not known a frame tx to fail in these or the 1400 series, but there's always a first time. I should have a 1400 transformer somewhere which should be sutiable. Cheers, Brian

6th Oct 2006, 10:26 pm	#3
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Fergi 3821/ 1500 chassis frame collapse Check the height control - it's a skeleton pot on these and it does tend to go intermittent or die. Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

6th Oct 2006, 10:49 pm	#4
tvden Retired Dormant Member Join Date: Oct 2003 Location: Halesworth, Suffolk, UK. Posts: 413	Re: Fergi 3821/ 1500 chassis frame collapse Hi all I will have another look at the set over the weekend re your suggestions, and see if I can find anything. I think it would be a good viewable set if I can expand the frame! regards Den

7th Oct 2006, 5:24 pm	#6
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	Re: Fergi 3821/ 1500 chassis frame collapse Hi Never had a tx go either - but they do go very waxy. Don't forget the TWO 330k (ish) resistors in series with the height pot as it's fed from the boost line - one's near the LOP stage and can be missed - aim for around 250v at the 'top' of the height pot. lyn

7th Oct 2006, 7:10 pm	#7
dazzlevision Dekatron Join Date: Sep 2003 Location: Near Swindon, North Wiltshire, UK. Posts: 3,612	Re: Fergi 3821/ 1500 chassis frame collapse Hi, There are two 18k 0.5W resistors in the frame linearity feedback circuit. They are unreliable in this chassis. Regards, Dazzlevision

7th Oct 2006, 9:30 pm	#8
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,965	Re: Fergi 3821/ 1500 chassis frame collapse I agree with all that has been said. I seem to remember an electrolytic cap, abut 1uf just off the boost line on the feed to the height cct which use to play up. Sometimes it just dried up but occasionally it would go leaky or short circuit. If you have a cct diagram and a meter the 1500 is one of the easiest chassis to fault find on. Oh don't forget to keep the brightness turned down with frame collapse, this will avoid any risk of phosphor burn across the screen. __________________ Simon BVWS member