At a bit of a loose end today so thought I would have a look at this set
I've been thinking of offering this set for exchange for a PYE set of equivalent age/ size
Without even touching it .
It's a Ferguson 3713 fitted with the Thorn 8500 series chassis
On removing the back cover I was pleasantly surprised on how clean & almost like new condition it is , no years of dust ,no nicotine stained plastic & no corrosion well the tiniest bit
It looked like it had just been taken out of the box
It makes you feel like just plugging it in & tuning in
There are 2 green smoothing caps that have leaked
The one you can see is a 700uf 250 volt
The one under the dropper is a 400uf 350 volt
I have 2 600uf caps & was wondering if I should give them a try
They should work fine. They will need to be re-formed before using them if they are NOS ones, Malc.
A good one Chris, looks to be a nice set
I've still got 8000/8500 power supply elcos in stock, real 1970s stuff, will need reforming before you use them.
Having reformed 2 nos 600 uf smoothing capacitors & fitted them
I then powered up but the cut out popped out immediately
Not finding any shorts around the power supply area , l decided to have a closer look at
The line output transistor , not short , but it was leaky from collector to emitter
Fitting a new one & replacing the 002 uf 2kv on the same heat sink
I then had EHT but smoke . R402 has burned up not having a manual for this set I'm not totally sure what it feeds .
It looks like it supplies w403 diode
Can anyone help ?
Not related to the current fault, I've also read that on the same panel you should check R404 33KR 1W as it frequently fails. It feeds line pulse to the decoder. Apparently later boards had a wire-wound resistor in this position.
Don't forget all the 8000 stock faults apply to the 8500 of which your current fault was included https://www.radios-tv.co.uk/brc-8000-stock-faults/
Replace R402 & W403 as a precaution but the fault was traced to the red A1 pot had tracked across the back
Now I have a raster but out of focus , looks like the focus unit has failed
Or the EHT rectifier tray
If its the EHT tray I have plenty in stock, if you need one you're welcome. The focus units on these sets are dire after all these years, "Thick film" types.
I had the same defocussed fault with my focus unit, had to buy a new one.
The tray is a common cause of focus problems on the 8500 it was the first part that failed in my parents set it was about 4 years old at the time.
I had to change the LT smoothers last year as one suddenly went o/c while I was watching it.
That looks like a nice clean low hours set. I have yet to have a look at the one I got from Neil but somehow I don't think it will be as nice as yours inside!
Is the focus unit a standard type or a special to this set
The reason I ask this is I tried a focus unit but made no difference
I had a load of NOS focus units in stock that looked identical but failed to work, this was due to them having varying resistive properties. The ones I had were not compatible with the 8500 despite outwardly looking the same.
Beware all focus pots that fit this set despite appearance, are not equal.
I had to buy the specific one for the 8500. Unfortunately they are now out of stock from where I bought them. I will see if I kept the data for it.
The 8500 Focus unit must read as follows:-
Between the left hand pin (+) and the start of the wiper track its needs to measure 17.6 M ohm
The wiper track itself should measure 30 M ohm
Between the end of the wiper track and the right hand pin (E) it should measure 26 M ohm
Thanks for the info Chris
I'll give it a go with some measurements