1971 Ferguson 3712

BRC/Thorn 8000 Chassis

Model: Ferguson 3712

Year:1971

System:625 Line

Original List Price : £182.90

Valves: None

Transistors:Yes

CRT: A44 271X

Brochure Picture

The Actual Set

I’ve been after one of these early single standard sets for some time they were quite a milestone as they were the first sub £200 colour television to be available in the UK. This enabled a vast number of folk to experience for the first time, affordable colour television.

I put a request out in the forums wanted section looking for a Fergy 3712 or Marconiphone 4712. I was happy to take on anything and that included basket cases. To my delight forum member BRC 3000 (Dave) came up trumps, with a basket case, thanks Dave.

The set has a number of challenges here are just a few, there’s bound to be more discovered as time passes :-

  • Missing its back cover
  • Missing its timebase
  • Missing PSU and sound module
  • CRT PCB cracked in half. One of those halves is also badly bent and almost in half again
  • Chassis is badly corroded and components badly corroded.
  • CRT is low
  • Control knobs missing
  • Thorn tuner will not latch on any channel (usual washer failure)
  • Tuner mounting to cabinet, one mount point thread stripped
  • Aerial input socket severely corroded
  • Cut-out severely corroded
  • C714/C715 smoothing can badly leaked electrolyte
  • Dropper severely corroded
  • Purity rings corroded
  • Many pots and pre-sets are heavily on various parts of the modules are corroded and in some cases seized
  • Signals panel mounting pivot broken loose
  • Front CRT fascia has been painted matt black as well as half the tuner control panel. This should be silver.

Although the list looks daunting, all should prove to be fixable. The CRT PCB is a bit of a worry but I’ve stitched together a busted 3ooo line-timebase so chance to practice those skills now on the 8000 CRT PCB base.

The CRT has been left cooking on the B&K 467, after an hour it has shown no signs of improvement. This is the only worry, looks like it will need a bop  Still at present that’s the least of the problems the set does seem to have been stored in damp conditions during its life. Certainly parts of the chassis seem to have been in water contact, there’s even a tide mark on the signals module. This set will likely present many opportunities for component replacement.

Unfortunately this set is non starter at present until I can find a missing PSU/sound module. The CRT PCB I may be able to repair but it would always be a worry due to the extreme damage. Assuming I can get it running then there will be the cabinet front to tackle, it will need to be resprayed to its original silver finish. Only time will tell how this one develops so do check back as I tackle this poor old Fergy 3712 but for now that’s it I’m afraid.

CRT Update

After 2 hours no improvement so I ran a clean & balance on all three guns. Red and Green responded well, blue however needed a couple of goes before life was seen. Now the CRT reads good on all three guns.


Update: Extraction

Time to remove the messy chassis and see what we’re dealing with.


Due to the many problems but mainly the missing PSU/Snd sadly here ends the repair……well for now.

CRT PCB Repair

Joined the parts together, just need to stitch the tracks now.

And the final track stitch


Cabinet Refurbish

Whilst waiting to figure out the plan of action for the missing power supply, I turned my attention to the very sad cabinet. In the past some bright spark had taken to daubing the front fascia in black paint, this would be returned to silver. I would also need to search my stock of badges to see if I can recreate the Ferguson logo and text.

Here are the results of an afternoons work, its not perfect then neither is the TV but…. Its way better than before.


Chassis Rewired from 8000 to 8000A:

The reason for this modification is to address the missing PSU/Sound Module. I don’t have an 8000 PSU in stock but do have an 8500. The following information provided by an observant Jayceebee (John).

By Jayceebee

Below are the modifications to convert the wiring harness to an 8000A and enable the 8500 psu to be used, no modifications are required to the actual board. None of this is my work Chris, it’s all documented in the manual, I came across it by accident.

1. Trace the red/orange cable from 11/5 on the timebase board, it should go to 10/1 on the psu. Remove it from 10/1 and connect to the lower connection of the new R729 1k section of the dropper

2. Add a length of wire from the top connection of the 56ohm section on the dropper (new R727) and connect to the junction of L406/C444

3. Disconnect the lead from 11/1 which goes to 10/8 and connect to 10/1

4. Add a link from the top connection of R709 to the junction of the 56ohm and 1k (new R727/729) sections of the dropper.

An inspection of the original 8000 dropper showed the R709 section had been smoking the weed! its way high 😆

Luckily I have a new old stock 8000A dropper in stock. Interestingly the 12R section on this one also has a 6R tap. I’ll get on with the rewiring a little later and the chassis repair work will continue in this repair blog.

Work Begins On The Chassis

And now the rewire to 8000A spec to allow the 8500 PSU ( centre of chassis) to be used.

Chassis Rewire complete: Dropper connections

At last a Power Supply and Sound Output Module Installed

Next steps…..  replace the leaked multi-can electrolytic. Then due to the original open circuit 47R dropper section, check the line output transistor and tuning capacitor as one or both of these may be fried. Not forgetting yet another Thorn tuner repair due to washer rot, still this will be the 6th or 7th one I’ve done now so I’m getting quick at them now.


C714/C715 2500uF 63V 500mA ripple electrolytic replacement

Do you think I should try and reform the original……. Nah I have a new one in stock, though that one I will reform so as not to stress it after years of being dormant.

New electrolytic being reformed to rated voltage on the bridge.

New electrolytic reformed and installed

With the PSU/Sound module installed, wiring harness cleaned and re-strapped where sticky tape had failed, Its starting to look a much more presentable chassis now.

The final tasks before initial power application are checks on the line transistor and remove the green meanie. Last but not least fix that seized Thorn tuner. Hopefully power by the weekend.


Having fixed the Ferguson 3734 9600 the main bench has now been freed up for the 3712.


Tackle The Tuner; BRC ‘Washer Rot’

Frequent visitors to my repair blogs or forum threads, will know about the dreaded BRC/Thorn tuner washer rot. I’ve tackled countless now and the procedure is well documented but if you’re new here and have stumbled upon the blog, then the procedure is detailed here.

The tuner in this Ferguson 3712 has the problem, therfore If I want to be able to progress this set and attempt signal acquisition, the tuner needs to be repaired.

And then it was repaired

The Fergy was missing one bright from one of the tuning buttons and missing all its control knobs. No problem I have a stock of vintage CTV knobs, here is just a small sample of some of the stock, there are a few more larger draws to call into action if required.

CRT PCB broken component replacement


Final Task- prior to power up

Line output transistor and Flyback tuning cap checks

VT401 is a BU105/02 and tested OK.

The flyback tuning capacitor C406 tested OK but these green caps although looking innocent, don’t age well. They tend to start to bubble away shortly after application of power. You have to remember the tuning cap is subjected to the high frequency switching and pulses of the line output stage. If this cap fails you can end up with sky high EHT and the consequences of that are not good.

The cap value is 1N5 @1500V. Typically I have all sorts of flyback caps in stock but sods law not these at that voltage. I’ve ordered a whole load so the first application of power may have to wait for them to arrive. I might go for power up with the drive to VT401 disconnected and see how the rails fair, we shall see……


The chassis and cabinet after some TLC

The chassis :

  • De gunk chassis of filth
  • Fit missing timebase
  • Repair broken CRT PCB
  • Fit missing power supply & sound module
  • Replace Dropper
  • Rewire harness from 8000 to 8000A so as to accept 8500 PSU
  • Repair seized tuner and replace knob bright
  • Replace C714/C715 and reform
  • Reform C704 C706
  • Repair CRT dag
  • Repair CRT dag straps
  • Clean & Balance Red, Green & blue CRT cathodes
  • Fit 5 missing control knobs

The Cabinet:

  • Clean & de-gunk
  • Return fascia to silver by respraying
  • Clean and remove black paint from control fascia
  • Fit Ferguson colour logo and model logo
  • Clean, touch up cabinet and polish

Before

After

Before

After


Next?

The fun begins as it will be power application, then the real work begins….. component level diagnosing the no doubt many faults that exist in the electronics. If the other poorly stored sets I’ve worked on are anything to go by, there should be some interesting times ahead.

Remember to check back soon…….

3 thoughts on “1971 Ferguson 3712

  1. Hi Mike,
    I was reluctant to do it but after one hour at 6.3V the a further hour at 8V the emission showed no sign of creep-age upwards. I then ran a clean and balance on all three guns and that seems to have done the trick, fingers crossed it remains that way. Blue was a real pain it did not want to wake up. I think this set is going to be a real challenge as it certainly suffered some sort of damp storage.

  2. Well this set has certainly gone to the right home. I got it from a long retired tv engineer in Bournemouth. I collected this set along with more than 50 others from him last year as he was clearing out his house with a view to downsizing. A lot of the sets were rough though there were some gems amongst them too. This set I kept as a parts set in case I could find another 8k to make a good one up. However seeing your wanted add made me wonder if it could be saved. Looks like it might live again one day, if certainly looks a lot better already. I will follow this thread with interest. Good luck Chris !

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