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1970 19" Ferguson 3703: BRC 3000 MK.1 Chassis

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crustytv
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Continuing my journey with the BRC/Thorn sets I thought I would have a look at my Ferguson 3703. I keep apologising for working on Thorn and solid state sets however I find them fascinating and the education value they supply is always worth the effort, so I'll stop apologising now. The winter project will satisfy the something different folk and it will be a very big challenge.

Back to the Fergy, I do love the style of this set and only wish I had the original stand, I may just find a local chippy to see if he can copy from the brochure photo.

hmv3703-1.jpg

For those that may recall this set came to me about three years ago damaged having been dropped. Thankfully all the pieces were there and the set was pretty much in original untouched state, with plenty of scope for repair.  The drop had resulted in the fascia being smashed in several places but thankfully the CRT had not taken any damage. I managed with fibre-glass matting and epoxy to make repairs to the fascia.

hmv3703-8.jpghmv3703-6.jpghmv3703-7.jpg

Once reassembled the set sort of worked, the CRT was low but benefited from a clean and balance. The set had many developing problems, one being shading to one side of the picture. All boards looked to be complete but with many components looking the worse for wear and the heat-sinks were missing from the RGB drive transistors. The set was put to one side as at the time I had just embarked on the Baird 8724 build which was all consuming.

Roll forward to today, I had just put the back on the HMV 2725 and thought what little project I could fit in between now and the winter project. That's when the Fergy 3703 sprang to mind, its small easy to grab from the TV display room and man handle to the workshop. This was duly done and power was applied with the intention of giving it a baseline assessment,  the result of which was to find it dead.

I could smell the familiar dropper warming up and the CRT filaments were visible, a quick investigation showed the 58-60V rail was missing ( a common theme ). The 30V rail is sitting a 39V. The Line timebase was drawing excessive current as R907 (1.5R/5W) was hot and puffing smoke. Whilst rapidly checking other voltages there was a loud crack as some cap or resistor decided to fire off, almost made me soil my gusset bang_gif

So that's the starting point then, the PSU out onto the test rig for some initial investigation and testing and the LTB to check. More to report a little later.

3703-1.jpg3703-2.jpg3703-3.jpg3703-4.jpg3703-5.jpg

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Topic starter Posted : 15/10/2016 2:18 pm
Anonymous
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that is spooky just put a bit of blurb about my set ! and it's one style I had been on the look out for ages.

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Posted : 15/10/2016 2:20 pm
crustytv
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Hi Pasty,

Spooky indeed, I had no idea you had posted as I was typing my thread up as you must have posted yours. I was very confused when I look in the TV section, I thought I had type the thread title in wrongly then realised "OH wow! what a coincidence". If you would prefer I can hold off on my thread I don't want it to detract from yours.

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Topic starter Posted : 15/10/2016 2:25 pm
Anonymous
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Hi Chris don't hold off I have all my g clamps on the modified bush stand so they won't get to the set for a day or 2. The set has been on my bench (which is in my office at work) for 3 months since picking her up from Neil. I was in no rush to start work, I won't be adding any more for a little while. Chassis is out, serial number 3792 and it looks like the original one as its a 3703 model on the plate. Looks like the top bowed and the strengthener cracked due to another set being on top. I am confident it will look fine when done. Great to see your set on bench too !

Funny I too have a colourstar  3705 too ! nice set all round bought from an ex thorn service depot engineer. That one was being used by an old dear right up to the digi switchover. The factory and depot in Enfield and Edmonton was just a few miles up the road from where I grew up - hence plenty of 3k's at the local tip to play with when I was about 14 !! Regards Stuart, off to Port Wenn, sorry Port Issac now for a wander and a pint of Cornish ale - ansum !

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Posted : 15/10/2016 2:38 pm
crustytv
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Diverted by other chores, I'm now back at the bench and this dead 3000.

I removed the PSU to give it an inspection prior to the usual Spatch-Cocking for the Test Jig. First observations suggest this ones seen a lot of use, I guess with the smaller cabinet the heat generated and captured cooks things up a tad.

The 60V and 30V fuses are intact, that's good. I may have found the source of the loud crack, it being C624 a Callins which has shed its coat at one end. R642 looks really burned up too. Both these are in the 30V line. C608 looks poorly as do most of the other Mullard tropicals which are cracked and crumbling.

Just before I open it up I loaded the PSU on the test rig to check the voltages. The immediate thing I notice is the 30V rail light is illuminated and very bright. A quick check of W605 anode and cathode reveals they are both sitting at 40V, this means the 30V zener is short-circuit and has undoubtedly destroyed the delay switch VT602. Junction of R607/C608 was also cooking, its voltage was at 4V no doubt caused by the Chopper drive transistor VT605 being switched hard-on.

3703psu-2.jpg3703psu-1.jpg

The two callins caps, C618 was o/c and C624 was high ESR

c618.jpgc624.jpg

 

Well the next step is to spatch-cock the PSU and replace the failed components, check the burned up R642 and replace a couple of essential resistors then see where we are.

More to follow......

p.s. The filter cap across the on/off on this set is dated Oct 71 so in all likelihood dates this set to then. Spooky as its exactly 45 years to the month. Oh and the Tube was replaced on 15/ Nov/1980 as there's a Teletronic card inside from where the CRT was sourced so that's 36 years old now.

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Topic starter Posted : 15/10/2016 8:07 pm
crustytv
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Slow progress this evening, being distracted watching 70's corrie episodes on the 2725, hopefully play catch-up tomorrow.

I did get around to opening up the PSU and loading it into the test rig. Despite the rather worn and tired appearance up top, the print-side of the PCB although dirty will clean up. Unlike the Ultra's PSU this Fergy's PSU tracks have not suffered from lifting or abuse due to many past repairs. 

3703spatch.jpg

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Topic starter Posted : 16/10/2016 12:54 am
Anonymous
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a possible solution for Chris's 3703 lack of stand leapt out at me in ikea they have a black stand for just £9 that doesn't look too far off the original, it has a shelf which could probably be taken out and the whole thing can be cut down to suit

Key features

  • The opening at the back allows you to easily gather and organise all wires.

Assembled size

Depth:
26 cm
Height:
45 cm
Max. load/shelf:
10 kg
Max. load TV:
30 kg
Width:
90 cm

Package size & weight


TV bench LACK
Article no:
902.432.97
Package :
1
Length:
91 cm
Width:
37 cm
Height:
7 cm
Weight:
6.72 kglack-tv-bench-black__0193988_pe350210_s4.jpg
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Posted : 25/10/2016 1:01 pm
colourmaster
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Hi 

I just noticed that you mentioned the original stand for this set .

i don't if you knew but the 192 and 252 models stand is made of metal .

I asked our local blacksmith a couple of years ago about making me a couple of stands for my sets but he has recently retired . 

Regards .

Gary

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Posted : 25/10/2016 8:45 pm
colourmaster
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 Hi 

Sorry about the typing error , it should read 19" and 25" . i didn't press the correct button .doh_gif

Regards.

Gary

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Posted : 25/10/2016 8:51 pm
Anonymous
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Hi Gary, very interesting Mr Bond....

Having never seen an 3 / 3k5 on any other than a wooden stand I assumed it was wood too ! all I have seen is the brochure pic on the website. The other early set I have is a 3705 25in 3k c/w teak style stand.

If you have any dimensions or photo's of any original metal stands I believe there will be a few of us keen to know more.

Whilst being very capable making a stand of black iron box tube I think it would be rather heavy, the Ikea cheat I saw could suit a broad range of sets with a bit of cutting about and for £9

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Posted : 27/10/2016 11:21 am
crustytv
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Wow! I cannot believe four months have gone by since I last looked at this, a prime example of procrastination, anyone else suffering with the same affliction? waa_gif

Anyway thought it was about time I got this Thorn 3000 MK.I Fergy 3703 that has been taking up bench space, up and running once and for all. So where did I leave off?

Well a check of W605 anode and cathode revealed they're both sitting at 40V, meaning the 30V zener is short-circuit and has likely fried the delay switch VT602. Also the junction of R607/C608 is also cooking, the voltage at 4V likely caused by the Chopper drive transistor VT605 being switched hard-on. I've started to replace the duff, cracked caps, will replace the 30V zener, check VT602 then see if we can get this PSU up and running. Once that's done I can then see what state the rest of the TV presents to me.

psu-1.jpgpsu-2.jpg

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Topic starter Posted : 19/02/2017 4:21 pm
PYE625
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Chris said
Wow! I cannot believe four months have gone by since I last looked at this, a prime example of procrastination
  

You have kept us in suspense for four months Chris..... Disgraceful ! grin_gif

Looking forward to reading all about it. No more procrastination here please, at least not on a Sunday.

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Posted : 19/02/2017 6:56 pm
crustytv
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Well as is the norm for me some success and then failure.

A pleasant afternoon at the bench replacing severely cracked tropicals. To replace the 30V zener neatly requires the small top PCB to be freed. This means the dropper has to be removed along with R615. R615 had one leg rusted through so a suitable replacement was found. With the dropper removed and the three retaining nuts removed I could now gain perfect access to remove and replace W605. As mentioned W605 was s/c and as suspected had also taken out VT602. When the transistor was checked it was faulty. VT602 looks to have been replaced in the past incorrectly with a BC182L, it should be a BC184LC or a BC183L (higher HFE devices) but I suspect the 182L probably worked though its not listed as suitable in towers.

bc182l.jpg

With a new the new delay switch transistor installed I thought I would now introduce the PSU to some power once again via the jig. Excellent initial results with the 6.3V, 240V, 30V and 58-65V rails being established. Then it went pear shaped with the 58V-65V rail light going out followed by extreme venting of magic smoke emanating from the supply near the 30V regulator VT601. A quick switch-off and a retreat from the pungent pong. After a couple of mins I decided to repeat the power application this time monitoring to see what was getting hot under the collar. It turns out to be R645(5R) which is in the base supply that is cooking up.

C609 was leaky as can be seen from the photo below and I now have 45V again on both ends of the new Zener, so looks like that's gone again, probably taken out the new delay switch transistor too. doh_gifdunce_gif

That's as far as I've got this afternoon.

r645.jpg

psu.jpg

C609.jpg

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Topic starter Posted : 19/02/2017 7:59 pm
PYE625
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The carbon resistor just below the green wirewound looks like it has had a hit too. 

It would be interesting to see if C609 reads the same out of circuit.

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Posted : 19/02/2017 8:29 pm
crustytv
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PYE625 said
It would be interesting to see if C609 reads the same out of circuit.  

Hi Andrew,

An in circuit test is valid for C609. I have spare PSU's and C609 should be reading as shown below on a good PSU not as I have above, its clearly leaky.

Working PSU, In-Circuit C609 test

spare.jpg

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Topic starter Posted : 19/02/2017 8:52 pm
PYE625
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Hi Chris,

That's a nifty little meter. Yep, that cap has surely seen better days.

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Posted : 19/02/2017 9:08 pm
crustytv
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As suspected  my new 30V zener and delay switch BC184L, are toast! electro_gif doh_gif

VT601 is also s/c, R645 has doubled in value from 5R to 11R and C609 is leaky.

deadthings.jpg

Any one of those failing (except R645) would prevent the 30V rail from establishing itself, so pretty much everything that could stop the 30V rail coming up, has failed

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Topic starter Posted : 19/02/2017 9:35 pm
crustytv
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PYE625 said
The carbon resistor just below the green wirewound looks like it has had a hit too. 

Sorry Andrew missed this comment, yes it does look rather horrendous. Its listed as 182K 20%, surprisingly though it reads at 172K which is well within tolerance.

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Topic starter Posted : 19/02/2017 10:20 pm
crustytv
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Picking up from where I left of yesterday. Before I replace the silicon carnage (VT601, VT602 and W604) I opened up the underside of the top PSU PCB, this again affords easier access for component replacement. It revealed a number of suspect joints and that C619 has a intermittent track fault in the negative supply. C619 was also leaky so C619 along with C604,C609 and R603 were replaced. Next the silicon.

psu-3.jpgpsu-4.jpg

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Topic starter Posted : 20/02/2017 1:40 pm
crustytv
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PSU transformer rubber mounts have totally perished. The transformer was just flopping about, theses will be replaced with new.

psu-5.jpgpsu-6.jpg

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Topic starter Posted : 20/02/2017 3:17 pm
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