Der 5744

[Focus Diode]

Originally Posted by pichacker

C631, And the choke core dropping out.. (LLJ)

I remember reading something Les wrote about one of these sets in which an "engineer" had misadjusted the 30V line to 40Vish to mask a "corrulgated verticals" fault which soon resulted in the faliure of a major component.

Brian

[pichacker]

Insert aerial. Colour o.k., sound o.k., picture rippled.
Slap another electrolytic across C619. Better but not
cleared. Check R528 (18Q, wired across L502). Turned to
dust. Replace, but hardly any difference. These components
are in the supply line to the line output stage: R528 is inside
sleeving, and is revealed when the beam limiter board is
lifted. Bearing in mind that there had been a difference when
R528 was fitted, we tried a capacitor of around O.l5prF
across L502. Ripple cleared. Funny. Enter friend Ray.
"Can I take a set-top aerial to try over the flats Les?" he
bawled.
"Of course. I say, why should a capacitor across L502
stop a ripple usually associated with lack of smoothing in
the chopper line?"
"Cos the core's dropped out of L502 and it's not
smoothing. I thought everyone knew that" said Ray.
"Of course, of course", I mumble

May 1987 P382

If you haven't already got it, search for and download the LLJALL.pdf file. Fascinating reading and easy to use PDF search to find a particular chassis.

[1955APREN]

hi
this could be due to over current trip circuit on the power board operating too
early look for a 2watt carbon resister on the lower pcb i think it might be 1.8k or a 2.2k it will have gone low in value and might be getting warm. regards
Derrick

[Davewantsone]

I am in the process of repairing a HMV 19 inch 3k.
I have been repairing the power board and have got as far as getting a picture with cogging and singing. About 1 inch in amplitude on both sides of the scan.
I have replaced C619 140uF (a 220uF was fitted by someone before).
R618 has been checked 150ohm.
C631 replaced (10nF)
W619 replaced.
I have already changed
W605 was zenering at 29V
C609,
C623
C624.
The fault is on this board as I have tried a known good power board.
Any ideas?

[Davewantsone]

Well I sorted out the cogging and singing.
R628 which according to my circuit should be 2 ohms but had a 4R7 fitted. I had ignored this for it was as originally fitted.
Now the Sept 77 Television magazine servicing details also shows this also as a 2ohm resistor.
So I fitted a WW 2R2 and no more cogging.
Could the board be a 3k5 model?
Does anyone have a circuit diagram with this resistor as 4R7?

[Lloyd 1985]

Hi,
Just checked through both the 3000 and 3500 manuals, both state that R628 should be 2 ohms, I also looked at the 3000 modification sheet (mk II) and it's not mentioned as being changed at all on there, Looks like someone fitted the wrong value to your set!

Regards,
Lloyd.

[Davewantsone]

Thanks for checking. The resistor position for R628 was on the underside board which if different than the green 2 ohm resistor normally fitted on the top board which is the case for the other two power boards I have.
The resistor looked as if it had always been fitted since when the board was new!

[Tazman1966]

While looking up some other info on the Thorn 3000 series I came across this old thread and wondered if you ever got to the bottom of the fault Gary?

Regards,

Tas

[1955APREN]

Hi
This fault is possibly on the power supply.

It could be the over-current trip circuit operating too early.
Possible cause is a 2 watt carbon resistor mounted on the lower psu board; it stands vertical near to the over-current preset. I think it is a 2k2 but not certain; it goes low resistance.

Regards Derrick

[System A]

Hi
To be honest I put the set to one side and have forgotten about it.
I'm recovering from an arm injury at the moment, so can"t lift tellys.
Once I'm fit I'll get back to the set and see if we can get to the bottom of it.
Regards.
Gary.

[Tazman1966]

Take care for now mate. I look forward to the telly's next outing