Hi Folks, got an issue with my Ferguson 3792, it's been working great since I acquired it, but last night without warning the whole tuning system suddenly failed. You can see from the attached photo there's a raster clearly there still and some quite white noise through the speaker, so amplifier and frame out stage are obviously working fine, but no snowy screen on any channel.
Checked the TDA2540 demodulator IC and it seems to be getting 12v to the appropriate pins, so the power supply must be working to that part of the circuit.
Any advice on how to continue diagnosing this issue would be much appreciated.
Hi Folks, got an issue with my Ferguson 3792, it's been working great since I acquired it, but last night without warning the whole tuning system suddenly failed. You can see from the attached photo there's a raster clearly there still and some quite white noise through the speaker, so amplifier and frame out stage are obviously working fine, but no snowy screen on any channel.
Checked the TDA2540 demodulator IC and it seems to be getting 12v to the appropriate pins, so the power supply must be working to that part of the circuit.
Any advice on how to continue diagnosing this issue would be much appreciated.
try to measure on the tuner, if you can locate around 38,9mhz from it, you can locate the fault to to IF, do you have a schematic? i would like to watch 🙂
it seems to be easy, if we have raster on the screen, and the tuner works, the fault has to be tda2540, but try to measure the voltage to it, maybe its gone?
Managed to get a service sheet for the TDA2040 cause I had my suspicions about that going, got 12v going onto it, so the powers supply is ok, seems a cheep part to get, so might try swapping that out
Does sound like a faulty TDA2540 or SL143x, note there are two version of the PCB. In early version the SAWF driver was a Plessey SL1430 which was extremely reliable, the same cannot be said of the later SL1432 which usually caused very low gain and they are not interchangeable. The set will still produce snow even with no tuner fitted.
TDA2540 seldom fails, but often have found capacitors in the AGC circuit give blank raster symptoms and would suspect C47 (0.1µF ) electrolytic capacitor, or maybe (horror) tantalum shown in the schematic excerpt posted by Chris. Also C35 (1µF ) and C36 (22µF) might be worth a look.
Does sound like a faulty TDA2540 or SL143x, note there are two version of the PCB. In early version the SAWF driver was a Plessey SL1430 which was extremely reliable, the same cannot be said of the later SL1432 which usually caused very low gain and they are not interchangeable.
Just to clarify you can fit a board using an SL1430 in place of one using an SL1432 and vice versa, it's just the ICs which are not interchangeable.
Agree with Rich that failure of the TDA2540 and also the SL1430 was very rare, don't think tantalums were ever used in the TX series.
She's Alive! Thanks folks, you were right, it was the TDA2540 on the IF board. Many thanks for all your help and suggestions. It's always a huge sense of a achievement being able to keep these great old sets working. ?
From the research I've done, it's from 1981, so your right about the era, the case is actually plastic made to look like wood which narrows it down to that time.
It's a great picture considering the age, according to the folks I brought it from it was actually used as a main telly up untill recently, so a tribute to the reliability of these sets. Incredible sound quality too on these, nice warm deep tone from the large elliptical goodmans speaker.
