BRC/Thorn 3500 Chassis
Model: Ferguson 3710
Original List Price : £301.80
CRT: A67 120X
The Actual set
Overall the TV is generally in good condition.
This TV has an unusual gimmick for channel selection, It uses a standard Thorn mechanical tuner located behind some 45 degree mounted flappy paddles. Behind these paddles are the usual protruding channel selectors, the paddles are just pushed against the protruding selectors, as I say gimmick!
The tuner is not working in as much as no channel selector will remain locked into position. This is due to the usual disintegrated washers and the method to repair covered in the link below.
Another thing noted is two of the A1 switches have been removed and replaced with wire links, this will be reinstated with stock from spares. The video module uses the thick film unit, these often give very poor grey-scale.
The left-hand chassis mounts have suffered damage in transit, despite the set being on a palette. The left-hand side vertical support has taken a blow and cracked away from the cabinets horizontal cross members. This should be a relatively easy fix, just glad it appears the CRT neck was not damaged when this happened.
Chassis vertical mounts broken from cabinet horizontal, I used quick set Gorilla glue for the repair.
Next job is to remove the tuner dismantle it and perform the washer replacement. Then the CRT will be tested shortly thereafter.
As suspected the tuner is suffering from the dreaded Thorn washer disease. As mentioned above this is a really simple fix and the link how to do so is above so I will refrain from boring you with the detail. I will just show the picture as it is now and then one after I have repaired it.
The second picture below clearly shows the extent of the washer degradation, none of the channel selectors will lock.
The Tuner dismantled, I think some service engineer in the past used cooking oil as a lubricant as the grease was thick and gooey. Now to clean, oil and fit new cups.
Parallel Task: CRT Test
CRT is good
Like Marty McFly “Back To The Tuner”
The new cups fitted and the tuning cores all oiled with fine clock movement oil. All that remains now is to reassemble and refit.
Tuner now repaired and operating smoothly, just needs reinstalling in the set and we’re good to go.
Next Day Update
Repaired tuner fitted and it operates perfectly now, should give many more years service and far less likely to fail due to the better cups fitted.
As mentioned earlier in the blog, two of the A1 switches had been linked out on the convergence panel. This is normal, when the A1 switches fail and a replacement is not in stock, engineers would often link them out. Basically a wire link is installed to make the switch connection in the permanent “On” position. What is astonishing is the wire links I found were just loops of solder !!!!
I have replacement switches in stock which I will in due course be fit, but for quickness to see what results I get on screen, I’ve temporarily installed proper “wire” loops.
The results are fairly good, the picture is a bit grainy, we have very poor grey-scale and there’s some convergence to sort out. I think a lot of the problems on picture quality are due to the thick film unit on the video module. These film units were very unreliable and I’m sure I can see some grey-scale shifting going on which is very indicative of the module problem.
I do have NOS film units in stock, I will make the decision later as to whether I just replace the current one with a new film unit or revert the video module to the earlier configuration which employed six individual resistors. Three 12K 7W and three 56K 1W. I covered this mod in another blog article which you can read here.
More to follow……….