Ferguson (early 90s) TV Repair

[ljones0]

Hello all

Granted this isn't all that vintage(!) as I believe the TV in question was manufactured sometime in the early 90s. Still uses a CRT mind you! But just recently a TV I have here - a Ferguson M6373GH seems to have taken a turn for the worst.

The problem is that the TV will not come out of its standby mode. I've tried leaving the TV powered off for a long time (about a week) also checked the remote control, batteries, making sure nothing is connected into the TV (e.g. scart sockets) but it simply won't power on. It tries to but fails; no picture or sound. Power does at least seem to be getting into the TV as the red LED is on at the front of the TV.

My guess is that I'm possibly looking at some sort of power supply problem. I've managed to remove one of the boards (making sure any high voltages discharged first!) to take a look but there seems to be no sign of damage, no burnt out components and soforth. Seems to be one of those "everything's ok but it dosen't work" type of problem.

Here are some pictures of what I believe to be the power supply board. I guess my first port of call will be to check all those large capacitors on the right hand side of the board (would that be right?).

Must confess I'd rather save this not-so-old TV one of the very last CRT based devices in the household (and not contributing more to the eWaste stream either!).

Does anyone have any ideas what might have potentially died in this TV at all? I did a search for a circuit diagram for this TV/model number but drew a blank. Without it - it is like fumbling around in the dark not knowing exactly where to look! Is there anying most likely to fail on this model of TV at all?

Thanks for any help!

ljones

[FERNSEH]

I came across two of these sets still in use this year. Both connected to Freeview boxes.
Have you checked the line output transistor? It could be SC, if it is check the flyback capacitor.
When I return to the shop I'll have look in EURAS for any fault finding tips.

DFWB.

[HamishBoxer]

Check with head magnifier for dry joints around the line/line driver stage.

[ljones0]

Will do though I must confess I have nothing like a circuit diagram even to go on. Strange how some things work and go on for years then all of a sudden -- nothing! BTW is there any way to do a simple check of the line output transformer at all ( I lack the neccecary tools to do a more complicated test!). Would the flyback capacitor btw be that large electrolytic 385V capacitor btw? Will also look for dry joints.

>When I return to the shop I'll have look in EURAS for any fault finding tips.

Thanks for that

ljones

[Red to black]

Your set uses the Thomson TX92F chassis, you should be able to find a manual on line for this.

The 'F' suffix is most important, as there were major differences between the various versions of the TX92 chassis.

The lopt was notorious on this chassis, on the other hand it could simply be 'child locked'

[pichacker]

Is it just the picture or is the soldering in location A 10 looking dry?

[FERNSEH]

I might have a spare service manual for this set.

DFWB.

[Red to black]

Check the surface mount resistors RL 04,05, and 06 underneath the lopt (on the underside of the main board), it is hard to see if they are burnt on the picture.

If these are damaged, then the lopt is almost certainly U/S.

[ekcopyephilips]

Can you disconnect the collector of the line output transistor and switch it on to see if your B+ volts come up?

[ben]

The last one of these with 'stuck in standby' I repaired had the frame chip s/c , I think the feed resistor had also gone.

[ljones0]

Put up a couple of new images btw in response to the posts. For reply #6 here's an image and an image for #8 also.

Looking at the underside of the board RL04/05/06 don't look as if they are burnt btw. Not sure if the soldering at A 10 is looking dry btw -- apologies for the ropey picture on that one the other pics were taken in daylight, no daylight now!

>Can you disconnect the collector of the line output transistor and switch it on to see if your B+ volts come up?

Would do but lack experience not sure quite how to do that at all.

ljones

[Red to black]

RL 04,05, and 06 look ok, they usually have definite burn mark rings when the lopt fails, due to the way it fails putting EHT down to chassis, these resistors are in a chain to chassis from the "earthy end" of the lopt overwind.

[Clydeuk]

Originally Posted by ljones0

Put up a couple of new images btw in response to the posts.

On the left of your first picture labelled TL19 looks like the line output transistor. If you have a meter set to resistance check between the centre pin and the outer 2, if you get a low reading it's likely short-circuit. If you can desolder the centre pin marked C that's where you can measure if you have B+ (on the PCB trace not the desoldered component leg).

If it is shorted it could be due to the flyback capacitor mentioned, dry joints on the drive transformer (connected to the B leg of TL19), could be the LOPT, or possibly B+ too high (which may be caused by a bad capacitor in the power supply).

I don't remember working on one of these chassis but it is going back a fair bit.


Is that capacitor marked 14.4nF 1600v in your picture burned or warped?, I can't see properly but that is the flyback capacitor I think, only way to really test that is with a capacitance meter, or by replacement.


Just on a quick google search, is this what yours is doing?

Goodmans GD2880D TX92F Reverts to St/by aft init EHT rush & brief green LED TL41 BD681 (s.c.), RL47 3.3 ohms, DL21 BY228 ( S.C.), 1.5uF 160V.W. capacitor (o.c.)

No I don't think I ever worked on one of these, I probably left the trade before these started playing up, maybe I was lucky.

[ljones0]

Gave some of this a brief go this evening. Will try again properly either tomorrow or towards the weekend. I tried measuing the transistor TL19 though haven't tried desoldering its leg yet. As I read the transistor with a multimeter what sort of readings should I find -- would a low reading in the tens or hundreds of ohms indicate a short?

The readings I got between the C (centre) pin and the outer pins read several megahoms; swapping the probes around would read lower, around 26Kohms.

I also checked the capacitor 14.4nF/1600V on an ESR meter (which can do in circuit testing) and it read open circuit. Also tried checking the capacitance with a capacitence meter on an ordinary multimeter and I could not get a stable reading from it, it was jumping between 0.29uF and no reading, alternating between the two. Would it be better to remove it from the board first or should it read ok?

Will try to desolder the leg of the transistor either tomorrow or towards the weekend.

ljones

[Welsh Anorak]

Hi
A faint bell is ringing - if the set is locked out I think you needed to press and hold the P+ button. Might be completely wrong - it's a long time since I've done one of these sets.
Glyn

[ljones0]

Not sure if it ever went into any sort of standby mode to be honest -- it suddenly "stopped working!"

Anway I have removed the 14.4nF/1600V Capacitor from the board and tested it both with an ESR and capacitance meter. The EVR meter gave the same reading ("overload") while the capacitance meter showed the right value.

Will try removing the transistor closer to the weekend.

ljones

[ben]

Originally Posted by ljones0

Not sure if it ever went into any sort of standby mode to be honest -- it suddenly "stopped working!"

That changes things.
We need to know for sure:
a) if the set attempts to start the line stage - any static on screen when you switch on?
b) if the standby LED comes on, and if so is it flashing or steady?

The relevance of any advice we can offer depends to a great extent on these factors/symptoms.

[ljones0]

No problem. First of all the set might be trying to start the line stage. I'm not sure -- I've been told by other members of my household that they can hear the TV try to start the CRT -- after this however it fails and returns to standby. The red standby LED stays steady it does not flash at all.

ljones

[ben]

In that case, definitely check the secondary loads off the line transformer - frame, RGB etc.

[Okto1984]

Some of the soldering looks suspect to me, lumpy and not well adhered to the leads - and I suspect not original as they look different and have flux residues.

Whatever the case, I had some joints like this in my set, and they caused me a lot of trouble as once I'd taken the boards out, these not so good joints got worse from being disturbed and caused new annoying intermittent faults. These problems thankfully all vanished when I realised what was going on and re-soldered them (edit to add, I made that step sound much simpler than it was...). Anyway, may not be the cause of your fault, but if I did my project again, any suspect looking joints like that would just get redone from the start to be sure.