Ferguson 382U Firefly not playing ball

[PJL]

Shorting plates normally mean someone has been messing with it. It might be best to take it out, clean it thoroughly, and inspect it properly. The plates can also be realigned to sit centrally. The wiper on the shaft that earths the rotor plates must make good contact. After cleaning you can re-grease the bearings.

[el gringo]

Wow.. that's looking a little challenging to be honest.. I don't suppose there is a way of removing it without undoing all the tuning indicator thread?

Pete

[el gringo]

Update: Discovered the MW tuning coil had also been attached to R5/C17, but had become detached! ( To allow easier working, I'd previously extended the aerial cable by several cm, but missed this connection DOH ). The original aerial cable is in place.

We now have distorted, but working MW and LW! with just the internal aerial, there is a station - they are discussing Football, but it's fairly distorted, in that I need to tune slightly 'off centre' to make the speech distinguishable! It's prob around 260-275m?

So I guess I'll need to work out how to disassemble the tuning cap now..

Pete

[electrogram]

Just a thought, but are the shorts due to corrosion rather than the vames being misaligned or physically damaged, if so it is sometimes possible to burn away the shorts with HT voltage, I've done this a few times , makes a nice firework display in a dark room.

[Boater Sam]

Don't take the tuner apart! Getting the vanes spaced correctly on reassembly is not easy.

[Sideband]

How about some pictures of the tuning cap? If the vanes are not distorted or bent in any way it should be possible to clear any shorts without drastic measures.

[ms660]

Originally Posted by el gringo

So I guess I'll need to work out how to disassemble the tuning cap now..

I would fix the distorted sound first.

Lawrence.

[el gringo]

Hi Lawrence - I see what you mean, I guess with at least one frequency working, I ought to be able to diagnose the distorted sound?

Pete

[el gringo]

Originally Posted by Sideband

How about some pictures of the tuning cap? If the vanes are not distorted or bent in any way it should be possible to clear any shorts without drastic measures.

Hi Sideband - picture attached.

[ms660]

Yes you should be able to, the fact that you can receive a station means that the oscillator is up and running and that the mixer is mixing, the chances of a tuning gang being shorted across the whole of the tuning range except for the spot where you have received a station seems remote (but not impossible)

EDIT: Post crossed.

Lawrence.

[Mike. Watterson]

As a last resort I use alcohol on VERY fine wet&dry folded to be exactly the right width.

Once I used a sharp blade to cut off a "lip" caused by something had bashed the edge of the capacitor plate.

Never take a tuning cap apart.

Also never get oil or WD40 etc between the vanes as it dramatically changes the capacitance, so careful oiling bearings. WD40 and switch cleaners remove lubrication. I'd not use "switch cleaner" on a tuner either, some don't evaporate completely, neither does WD40. You can use alcohol (at a pinch, Boots Surgical spirit) to rinse off Oil, WD40 or grease that has got into the vanes. A light bulb and battery or DVM in beeper mode. you do often need to disconnect the stationary connection as it might be "earthed" via a coil or aerial loop. Usually the rotary part is earthed.

[el gringo]

Okay, done a bit more digging around and I'm fairly sure the Ferrite rod inductors are the correct way around, along with associated, C and R components. I can definitely detect 2 more stations, one could be Absolute Radio? and the other another, music station. I have the volume at max and they are all quiet and suffer from a hugely distorted audio signal

Any suggestions how best to trace this at all?

Ta, Pete

[el gringo]

Originally Posted by Mike. Watterson

Never take a tuning cap apart.

Thanks Mike - I'm totally for not trying to take it to bits!! .

[ms660]

Might be worth making sure that none of the control grids are floating.

EDIT: Post crossed.

Lawrence.

[el gringo]

Hi Lawrence - Just checked and all seem -ve.

[ms660]

I would normally check by measuring the resistance between the control grid(s) and HT -ve (chassis) and comparing with the resistances that should be expected according to the schematic, a bit out is usually no problem but miles out would be cause for further investigation even if it's not related to the present problem, the resistors used for the grid return to chassis are always high values (except the oscillator grid in comparison) and as such are sometimes prone to an increase in value from their original value over time so worth checking anyways.

Lawrence.

[Sideband]

You need to decide where the distortion originates. Touching the grid of the EABC80 (with the volume control turned up) should produce a good loud hum. Touching the control grid of the EL84 should produce a somewhat quieter hum. If you don't want to poke around the valve bases, touch the centre contact of the volume control. If there is little hum from the volume control (make sure it's turned to full or nearly) check the anode volts of the EABC80. This is normally fed via a high value resistor (typically 220K or thereabouts) and may have gone very high or open circuit. If so, this will cause low distorted (sometimes no) sound.

[Tim]

Hi el-gringo.

It is possible to check the diodes in the UABC 80 are working with the normal resistance range of your multimeter, and one of the few cases where this can be done.
The set has to be powered of course SO BE VERY CAREFUL, but it can be done. Indeed I have done it a couple of times, and actually used this technique to find a faulty diode in an EABC80(not dissimilar to yours.
One lead to cathode and one to anode of each diode in turn with your meter on ohms(k?). Then reverse and check again. Should get the expected readings for diodes(ie. high one way, and low the other)

I did one of these a number of years ago. ISTR I also had a few problems with broken connections on the wave change switch contacts. I wonder if they get bashed when manhandling the chassis in and out of the case.

[Sideband]

el-gringo has already replaced the UABC80 to get as far as the 'distorted sound' fault at present.

[el gringo]

Okay.. traced the distortion to the AF stage surprisingly - as my sig gen had previously sounded quite clean ( although that could have been a few components back now! ).

Using an MP3 speaker I can get nice clean audio on the grid of the UL84, whereas using an iPod as an audio input, I'm not getting much at all and very distorted.

I'm wondering if I've got some duff components around the output stage?

Pete