UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - My first foray into Old model TV repairs. Ferguson 991T.

Heatercathodeshort · 29th Sep 2020, 9:41 am

Hello Adrian, I don't want to crash into your thread so I will just post these two pictures of the results of my 991T chassis overhaul carried out over the last few days.

A couple of months ago I was presented with just the chassis from a 991T by another Forum member. The cabinet had been carried away by woodworm and was nothing more than powder.

On examination it was very much original and was tuned to channel 5 [Wenvoe] At the time I put it aside but your acquisition of another 991T stimulated me to put it on the workbench and see what it had to offer.

I won't go into the details but after a couple of days in the workshop I have the results seen in the pictures. There were a number of head twisters.

It may be useful to compare notes as you progress with yours.

I would only say that it is important to follow a plan. Power supply, Line timebase, frame timebase, signals, sync separation and finally sound.

The chassis is a high gain fringe model employing flywheel sync but it does not enjoy and form of vision AGC hence the sensitivity control on the back.

The line oscillator will not run if the 2X.01uf capacitors, [in my version they looked like resistors] inside the discriminator transformer are faulty and they will be if they are original as mine were. It's a delicate winding and care has to be taken when removing the can from the chassis. Take notes and pictures.

When the line oscillator is running a negative voltage of around 20V will be recordable at pin 2 of the PL81 line output valve. The .01uf coupling capacitor is an early must for replacement.

DVM's will give significantly high readings in sensitive parts of the circuit compared to those in the manual. No problem if you are aware of this but you can't beat a workable AVO 8 when working with these old receivers.

Components have a 20% tolerance so for goodness sake don't go on a mad resistor change if they are just outside this. They have to be well out of tolerance to actually stop the chassis working, well out.

I agree a safe scope connection would be a help but I didn't use mine during the restoration of this one.

Good luck with it and I hope you succeed! Regards, John.

29th Sep 2020, 9:41 am	#39
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: My first foray into Old model TV repairs. Hello Adrian, I don't want to crash into your thread so I will just post these two pictures of the results of my 991T chassis overhaul carried out over the last few days. A couple of months ago I was presented with just the chassis from a 991T by another Forum member. The cabinet had been carried away by woodworm and was nothing more than powder. On examination it was very much original and was tuned to channel 5 [Wenvoe] At the time I put it aside but your acquisition of another 991T stimulated me to put it on the workbench and see what it had to offer. I won't go into the details but after a couple of days in the workshop I have the results seen in the pictures. There were a number of head twisters. It may be useful to compare notes as you progress with yours. I would only say that it is important to follow a plan. Power supply, Line timebase, frame timebase, signals, sync separation and finally sound. The chassis is a high gain fringe model employing flywheel sync but it does not enjoy and form of vision AGC hence the sensitivity control on the back. The line oscillator will not run if the 2X.01uf capacitors, [in my version they looked like resistors] inside the discriminator transformer are faulty and they will be if they are original as mine were. It's a delicate winding and care has to be taken when removing the can from the chassis. Take notes and pictures. When the line oscillator is running a negative voltage of around 20V will be recordable at pin 2 of the PL81 line output valve. The .01uf coupling capacitor is an early must for replacement. DVM's will give significantly high readings in sensitive parts of the circuit compared to those in the manual. No problem if you are aware of this but you can't beat a workable AVO 8 when working with these old receivers. Components have a 20% tolerance so for goodness sake don't go on a mad resistor change if they are just outside this. They have to be well out of tolerance to actually stop the chassis working, well out. I agree a safe scope connection would be a help but I didn't use mine during the restoration of this one. Good luck with it and I hope you succeed! Regards, John. Attached Thumbnails