Ferguson 3645 (BRC1400 chassis) raster but no sound or vision

[tvden]

Hi
This is the first dual standard set I have tried to get going, I have now put a new solenoid in this set but have taken it out of circuit via a switch inserted in the grey lead from the micro switch on the back of the VHF tuner, so I can now manually operate the 405/625 system slider switch.

So far so good - I have replaced a few caps where they were leaking.

I have a raster on both systems, my problem is I can't get sound or vision on 625 nothing from my aerial or a video recorder, and I have no signal source for 405 at the moment.
It's probably a valve or cap in the IF stage - anyone got any quick fixes for this board to pinpoint it?

many thanks TVden

[Steve_P]

When you switch channels on either system, do you get any sound or picture effects such as flickers or blips - this would show that there was some life in the IF stages?

I know you've changed the solenoid on the system switch, but have you checked the switch itself?
The tuner switching is done in the VHF tuner. Make sure it's OK.

Cheers,

Steve P.

[tvden]

Steve many thanks quick reply.

Yes, I did check the tuner switch and its working OK.

I should have been more explicit; when I change channels I get plenty of buzz/ hiss on sound on both systems and also plenty of flickers and blips, so there is some life in the set.

I will try and fix my 405/625 sig gen today and see if I can get anything on 405

cheers TVDen

[Focus Diode]

The VHF tuner acts as an amplifier on UHF. Failiure of the PC97 or PCF805 on the tuner would cause loss of signals at UHF as well as VHF, but that would usually result in a blank unmodulated raster.

Are the "biscuits" inside the VHF tuner clean and is the three pin black UHF tuner plug connected to the VHF tuner ok?

Unfortunately the UHF tuner itself could be faulty. I've experienced intermittent loss of signals with two of these sets due to the tuner.

The vision IF 30FL14 and Vision & Sound IF 6F29/EF183 are also worth checking.

The 30FL14 may be marked "PCF808". A PCF808 won't work however! I tried one once which resulted in the line timebase miles out of tolerance (doubles as the flywheel DC amp). Any valve marked 30FL14 is ok though, as are Mazdas marked both 30FL14/PCF808!

If need be a 6F30/EF184 may work as the video output valve if a 6F28 is not to hand. Indeed later Mazda EF184's are also marked 6F28!

Hope this helps!
Cheers,
Brian

[ScreenSaver]

Before delving into the VHF Tuner and the IF strip too deeply, you may want to just ensure that the 12v supply is reaching the UHF Tuner. It's developed across Z1 via R19 and is switched by S2b of the main system switch. Dirty contacts here, or a failure of R19, will leave the UHF Tuner dead in 625 mode, as well as 405 when, obviously, it should be.

ScreenSaver

[tvden]

Hi all

Many thanks replies: just a quick update.

I was able to put the ailing sig gen on 405 line and got a tone and a very iffy pattern, then whilst adjusting the line hold it just went off and left the raster.

So I now just have modulated raster on both systems; there was no smoke or burning at that point.

[tvden]

Hi all

Another update after replacing the PCF805 valve on the VHF tuner I got some sort of 405 back again with my ailing sig gen, but still nothing on 625.

I have tried changing all the valves suggested but no change; found resistor R97 (burnt) and put a new one in.
I have one of those magnifying lights and have checked the board for breaks/ bad joints but can't find anything looking on the populated side of the board; barring R97 I can't see anything wrong.

All other suggestions have been tried out but with no luck as yet.
Tomorrow I will check all the caps and circuit voltages; just wonder if it's the UHF tuner itself at fault?

The raster is full of tightly spaced fine horizontal lines.

Many thanks for everyone's help

regards TVDen

[Steve_P]

Change both valves - the VHF tuner provides amplification on UHF. By the way, R97 is on the audio output so it's very unlikely to be a cause of the problem.

Cheers,

Steve P

[Mikey405]

Hi TVDen.

I'm not quite sure whether you are saying that it is now working on 405 / 625, only one, or neither, but as has been suggested earlier by Screensaver, I would first check the supply to the tuner. I always get confused between clockwise anticlockwise and which pin is which on these plugs (and valves too), but it's easy becuase it's the middle pin of plug P1. Having a quick glance at the circuit diagram, you could check to make sure that the wipers on R5 and R6 are okay, and also that R4 (3.9M) and R7 (2.7M) are okay. Also R11 (2.5M) (the local / distant control) and R12 (27M). It doesn't matter if they're a bit out of tolerance, just as long as they're not open or have gone very high in value. Also make sure you've got 185v-ish on the anode (Pin 7) of V3, the 6F29 combined IF Amp and that R20 (27 Ohms) in the cathode hasn't gone open-circuit. Do you have a circuit diagram for the set TVDen? If not, I am happy to send you a photocopy.

Kind regards.

Mike.
PS. Do you have a 'scope? It would be very useful in pin-pointing the trouble if none of the suggestions work.
PPS. I use a Fergie 3652 (1400 chassis) in my spare bedroom for guests to watch and it has been unbelievably reliable. It's pretty much the same style as the "portable" model 3645 except it has a push button tuner along the bottom instead of rotary and it's 19" instead of 16". 1400s give off a wonderful smell all of their own after they've been on for a while.

[Mikey405]

I've just noticed that in some models, R4 is 3.3M and not 3.9M as I suggested earlier. Also I have had the BA116 (Double-diode W1 and W2 - Looks like a transistor) in the AGC circuit fail before, so you could check that.

Mike.
PS. If it's not working on 625 (or 625 AND 405), then I would be inclined to try and find the fault with the set switched to 625. I think it may confuse matters to keep switching between 625 and 405. If you find the fault on 625, the chances are it will also work on 405. Then again that's just my view and other people may say different.

[tvden]

Mikey 405, many thanks for input.

Although it is working on 405 this is only to degree and at the moment I have no proper 405 signal source, so I think you are correct in saying it's better to just get the set going on 625, otherwise I shall be going round in circles!

I am off now to have another go at it with your suggestions.
I have now got hold of the manual for the BRC1400 which gives me a nice clear circuit to look at

regards TVDen

[Focus Diode]

I can't help wondering if the original solenoid burn up has damaged the system switch in some way, perhaps at point S2B? It's worth temporarilly bridging to the 625 posistion to see if that helps, if the 12V supply to the tuner is missing. Obviously ensure the solenoid supply is disconnected first!

Putting Tag 43 to Tag 44 allows 625 VHF reception. With the system switch in the 625 posistion if this results in some activity on VHF the UHF tuner, or the supply to it would seem to be defective. Both contrast controls and the "local distant" control becomes functional on UHF as well as (405) VHF. Leaving Tag 43 to Tag 44 doesn't affect 405 VHF in any way.

Tapping around with an insulated tool can reveal faults- A fault I had was no signals for the first few minutes, then suddenly coming then going. Tapping the PC97 made the fault come and go, a replacement curing the problem.

If there's obvious IF activity at UHF it's possible the tuner itself may be at fault. Fortunately it's pretty standard although problems may arise in getting the controls to fit. With p/b tuners for instance the originals had 1/8" spindles with later ones (& 1500s) have 1/4" ones.

Check the components advised by others too of course. Sound advice from Mikey re concentrating on 625 first. Indeed they are extremely reliable sets when the initial problems are ironed out.

Cheers,
Brian

[tvden]

Hi all many thanks for all your input

I gave up on the 625 side as no checks revealed anything.

Now I have my Domino back, so went back on the 405 side, changed a few resistors and valves and I now have 405 line working OK. Needs a few tweaks but its basically OK, but of course noisy sound but this is well documented and I can fix this at a later date, and the tube is good.

Focus Diode, I have just read your post and will investigate, so as things stand at the moment I have reasonable 405 line working and I can watch a DVD OK, however switching back to 625 we are back to the modulated raster and mushy noise on sound.

I have tried all suggestions, bar Focus Diodes which I will try having a look at tomorrow as I will have a bit more time to spare this weekend, but any other suggestions welcome as to why this is not working on 625.

How can I test the tuner I dont have a spare (I will have to stick to single system sets in future) many thanks all

TVden

[tvden]

Hi all just a quick update just had a look at the set with the tag 43 changed over to tag 44, stuck the sig gen on and yes there is life on 625 VHF, so this means the prob is somwhere on the 625 tuner itself or the feed to it, looking at the tuner circuit I see it has them 3 legged things in it !!! I know nothing at all about this type of tuner and have never taken one apart, before condeming the tuner, I will now concentrate on the feed to it and see if I can find a fault here first, its a type T8 tuner

[Steve_P]

I'm back, just!, although in pain. Anyway....

Reconnect tuners properly, remove 625 Line VHF links, Switch to UHF.

12v Feed to UHF Tuner - Middle pin of 3 way connector. If it's not there, go to VHF tuner and check back to PIN 5 of the connection to the main PCB. Then check R3.

Another thing to try is to link, via a suitable capacitor, UHF IF O/P to VHF IF O/P. If this works, check the Coil Biscuit. It might just be mucky. Failing that, open the VHF Tuner and trace it through.

If it doesn't, then come back to me re:UHF Tuner.

Cheers,

Steve P

[tvden]

Hi all
Many thanks for all the input.

Steve, hope you are feeling better now.
I have tried everything you suggested and still nothing, so I think I have a UHF tuner fault, and will try and get the tuner out tonight, as I said before I have no knowledge of this type of tuner, from the wiring it looks like a varicap type with a couple of transistors.

The BRC manual states it should be sent back to the factory for repair, I might just have a prob doing that

When I get the cover off I might be able to see what is wrong, and I will also check the 625 aerial feed to it for shorts

[tvden]

Hi all

I finally got the tuner apart, and tested the 625 aerial feed which turned out to be OK, no components looked distressed at all.

I then had a good look at it under the magnifying lamp, and noticed that on one of the three variable caps the moving vane was touching the fixed vane, and the fixed vane could be moved ever so slightly, I then spotted a hairline crack in the solder attaching it to the tuning slug.

I managed to resolder it but I think a couple of vanes got moved slightly.
Anyway tried the set and it now works on 625/405 PK but the tuning may be out a bit on 625, the set still needs a few more tweaks in other places but its now a worker

Has anyone any experience of setting up a UHF tuner it looks tricky bending the moving vanes, many thanks for everyones help

[Mike Phelan]

Den
The vanes might be bent because someone has been at the earthing springs - they needed cleaning frequently on these Thorn tuners. May be worth a look at them as well.

As to fixing the bent vanes - the only thing to say is that it is better if it is not in the oscillator section (nearest to the IF output connection). On the RF sections, just trial and error; better if you only want to receive the five local channels as tracking is less of an issue.

On UHF, I always imagine tuners to be 50% electronics, 50% plumbing.
HTH

[Focus Diode]

Well done TV Den! Excellent news indeed. Apart from fixing bent vanes as Mike suggested I have no further experience with these tuners.

Don't touch the three tuning slugs at the rear though, I did this once which resulted in the channels becoming "Grouped", eg: for Group A with very poor results on higher channels.

Steve suggested removing the 625 VHF link. I used to use these sets as DXTV monitors and found leaving the link at Tag 44 gave higher gain on the UHF channels. This doesn't affect 405 VHF (with the solenoid "on") or 625 UHF otherwise in any way, but allows for 625 VHF as well with the solenoid "off" in the 625 posistion, not that it's much use nowadays unless you live in a favourable location . Really down to personal choice whether one wants this option I think.

Cheers and well done again!
Brian

[tvden]

well I finally got the set back togeather, as I was recording off sky at the time I thought I would use it to watch BBC on 625, settled down to watch but after 30 mins oh dear probs the picky started shrinking widthwise and there were a few nice trace effects on the screen looked just like the lopt had gone down after switching off and switching back on again there was no raster even but not to worry it was the rotten old bost diode given up the ghost,a PY800 had been fitted ? a newPY801 valve soon cleared the fault the set seems to be working ok now and gives a good bright picture I only have two dual standard sets this one and a KB, I might lookout for another suitable dual standard set in the near future but i hope it is more easy to repair than this one was