Der 5744

[System A]

Hi everyone , are there any ex DER engineers out there ? . i"ve started restoration on this ex rental set fitted with the BRC 3500 chassis . It has a strange cogging effect fault . i thought it would be cured by replacing C619 - 140UF on the psu board . i remember having a similar fault years ago . i "ve mislaid my 3500 manual so any advice would be grateful .
Regards . Gary .


Hi everyone,

Are there any ex DER engineers out there? I've started restoration on this ex rental set fitted with the BRC 3500 chassis. It has a strange cogging effect fault which I thought would be cured by replacing C619 - 140uF on the PSU board.

I remember having a similar fault years ago. I've mislaid my 3500 manual so I'd be grateful for any advice.

Regards,
Gary

[FERNSEH]

Hi Gary, Strange looking fault, have not seen anything like that in a 3500 before.
Got plenty service info for that chassis. Also I've got a spare RGB drive board if you want it.

Regards,
David.

[HamishBoxer]

That cap you mentioned, Gary, caused what we called in those days "crinkly chips"! This fault looks very odd and I wonder if indeed it's main smoothing cap on power panel.

These used to bulge and leak, certainly could indeed be a cap, then there's a 1000uF or similar on top of power panel that failed.

David GM8JET

[HamishBoxer]

PS Unless it's a weirdy IF fault?

[gec2110]

Could it be the position of the RGB LEAD in relation to interference?

[Lloyd 1985]

Hi,
Could it be something to do with the degauss coils being permanently on?
I would dig out the psu, and give it a damn good visual check, I had a duff thermistor on mine. I also changed a few electrolytic caps on mine before powering it up, as they looked a little crusty!
If you need it, I could copy my 3500 service manual, Might take me a while though Its the original Thorn one.

Regards,
Lloyd.

[Heatercathodeshort]

Never seen that one! looks like one of those pics you make by floating ink on water.
Just for the info the prefix numbers for Thorn sets are :

1 Philco
2 HMV
3 Ferguson
4 Marconi
5 DER
6 Ultra.
There may be more but those are the ones I encountered most. John.

[Philips Fan]

Wasn't BRC on the list too (or were they the parent)? I defer to you guys on this by the way.
Robert

[FERNSEH]

Hi John, I not absolutely sure but I do seem to remember that later Baird sets were given 77XX model numbers for Thorn/Ferguson made colour TVs. In 1969 Radio Rentals became part of the Thorn TV rentals group along with DER and Multi-Broadcast. Radio Rentals was considered the more up-market TV rental company.

Philips Fan, Not as TV sets, but I kind of remember that they did market a few items as BRC. British Radio Corporation.

DFWB.

[Nickthedentist]

Yes, I had some BRC-branded speakers supplied with a Goodmans Module-80 record player. 1973-ish?

That certainly is a bizarre looking fault, I too have never seen anything like it, and will be intrigued to know what it is when you find the fault.

[bobbyball]

Whatever you do, change the main smoothers - and any other electrolytics - anyway!

Robert

[pichacker]

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

However this is severe cogging. Can you hear the set squealing?

[Heatercathodeshort]

Very little luminance signal by the look of it. Have a look around the delay line for dry joints then do a bit of board swapping to narrow it down a bit. John.

[steve c]

1 Philco
2 HMV
3 Ferguson
4 Marconi
5 DER
6 Ultra.
There may be more -----

7 Multibroadcast
8 Radio rentals

[FERNSEH]

That's right, Radio Rentals was 8xxx. Remember the RR 8940 VCR?

That fault. It's most likely to be instability in the IF stage. First remove the luma drive to the RGB output board, the disturbance should disappear Any Callans elcos in your set? Change them before you do anything else.

DFWB.

[MALC SCOTT]

Make sure that the smoothing cap has not spewed up all over the video pcb.

[Welsh Anorak]

Hi
Philco? I always wondered what the 1xxx series were. When did they stop badging sets?
Radio Rentals sets were badged 'Baird', but as you say started with 8 for BRC sets.
Glyn

[FERNSEH]

I've got the 3500 series signal circuits service card in front of me.

Disconnect the luma drive plug PL/S10 from the IF board, that will establish if the problem is in the IFs. The other signal plug to disconnect is PL17, the R-Y and B-Y signals from the chroma decoder. Disconnect the tuner as well. The IF amplifier has four stages, transistors VT101 to VT104. disable each stage in turn by connecting a 1000pF capacitor between each transistor base to ground to determine the unstable stage.
As Malc says, check the luma board for electrolyte from the smoothers.

DFWB.

[Hybrid tellies]

If I remeber correctly that cogging effect could also be caused by faults in either the feedback or pulse width modulator on the psu. I seem to remember changing electrolytic caps, plus a few transistors and diodes. I will try and do some digging unless this has prompted somebody elses memory.

[MALC SCOTT]

I have a fully working 19 inch BRC 3000 here. You are welcome to try your panels in it to determine which one is the problem. Malc