Hacker Mayflower tuning problem

[Pilot Mariner]

A HM2 I am working on tunes normally from 104MHz to approx 90MHz where a local station CCR (Cannock Chase Radio) blasts in and swamps the remaining band down to the end of the scale. ie Radio 3 tunes normally at 90.5MHz, then CCR at 89.6MHz and then no signs of Radio 2 (88.3MHz), just constant CCR to the bottom end.

Another HM2 I have behaves completely normally, so a definite fault exists so not a location issue.

I presume the fault lies within the tuner box, is there anything else that could cause this before I take the trouble to dive into the tuner box.
What could be causing this sort of fault inside the tuner?

I have done the usual service on this set and the fault existed prior to the service.

Mark

[Radio Wrangler]

How well do other sets work at your place?

David

[Nuvistor]

Does this model have AFC, if so try turning it off, may be a fault there.

[Pilot Mariner]

My other HM2 works perfectly in the same location, as do my other working sets.
The fault is there regardless of the AFC setting.

[Nuvistor]

Have you a signal gen to confirm the tuner will work at 88.3, perhaps the tuner will not tune that low in the band?

[Pilot Mariner]

I've only got an AM sig gen which may do that frequency.

The HM2 should be able to tune to at least 87MHz

[frsimen]

As this uses permeability tuning, are the cores sticking at around the 90MHz position in the coil formers?

Paula

[Pilot Mariner]

Hi Paula - The bit of dial cord, one end of which wraps itself around the pulley rod when the tuning knob is operated, and the other end I presume is attached to the permeability slug in the tuner unit, moves freely without sticking along the whole length of the band. But I can't see what's happening inside the tuner unit. Looks like the next move is to look inside.

Mark

[Nuvistor]

Another possibility is that the RF alignment has been adjusted by someone to get a station a little higher than 104Mhz thus cutting off the lower frequencies.
Alignment instructions are in the manual for the RV20, is that the same radio as your HM2?

[stevehertz]

Originally Posted by Nuvistor

Another possibility is that the RF alignment has been adjusted by someone to get a station a little higher than 104Mhz thus cutting off the lower frequencies.
Alignment instructions are in the manual for the RV20, is that the same radio as your HM2?

Yes but R3 tunes in exactly where it should be, at the low end at 90.5. It would be upshifted if that was the case.

[Pilot Mariner]

Yes thats right Steve, from CCR (89.6MHz) upwards stations tune in where they should be, below that, CCR swamps the band down to the end of the scale.
I have tried adjusting the RF alignment to see what happens, but this causes strange effects, so I have left well alone in that department at the moment.

[Nuvistor]

Re #10 That’s a good point.

[stevehertz]

Mark, I realise that another HM2 works fine, but nonetheless a pointer to the problem could be that CCR now broadcasts on 89.6 (Cannock), 89.8 (Lichfield) and 94 (Rugeley). The fact that the bottom end is 'swamped' by CCR suggests a tuning problem (obviously) but selectivity maybe? I would imagine, in Burntwood you are capable of picking up all three of those? Like I say, a pointer to the nature of the fault.

[Pilot Mariner]

Good point Steve. I am getting the problem with just 6" of wire poked into the aerial socket. R2 is completely absent, it's as though the tuning stops at 89.8 but the actual tuning mechanism carries on, if this is possible. Maybe some sort of intermodulation is occurring somewhere.

[Nuvistor]

Did you try the sig gen to see if it will actually tune down to 87.5Mhz, if it will then intermod is a possibility but until you confirm its tuning range it’s difficult to be sure.
Switch off the AM Audio mod on the sig gen then and monitor the voltage across the AM suppression cap C25.

[Pilot Mariner]

Originally Posted by Nuvistor

Did you try the sig gen to see if it will actually tune down to 87.5Mhz, if it will then intermod is a possibility but until you confirm it’s tuning range it’s difficult to be sure.
Switch off the AM Audio mod on the sig gen then and monitor the voltage across the AM suppression cap C25.

OK I have found a way of injecting FM test tone signals.
It looks like the set will tune down to approx 90MHz. The set then stays locked to this frequency all the way to the end of the scale.
I have tried forcing through the R2 frequency @88.3 but nothing is heard.

Similar results are obtained using my sig gen, but CCR is always in the background even without an antenna connected.

[Nuvistor]

Did you check Paula’s suggestion in post #7? You were going to check inside the tuner. At least you know why R2 isn’t heard.
If the cores are moving correctly then it looks like alignment unless there is a faulty component.

[majoconz]

I had a similar problem with a Nordmende Globetrotter - but not quite! Being an early European, it only went to 104MHz and my favourite oldies station is on 104.2 - but also my VHF pantry transmitter is on 88.5 and there is a very good low powered local station on 87.9. Checking with my sig gen, it never even got up to 100MHz! Anything I wanted was going to be a struggle - permeability tuned too and you can only push a core so far into an inductor until it starts coming out the other end! The absolute lowest I could get it down to was the scale marked as 88MHz and then the frequency started going up again - I tried tweaking the high end trimmer but that dropped it right down to 98MHz. Moving some of the wiring inside the tuner finally got me down to 87.7Mhz but lost the high end again. (I'm talking microscopic movements here!) I brought it back up to 88MHz and found a serendipitous moment - the AFC would pull it down to cover the 87.9 station! Now to get the 104.2 station back in - lo and behold the same trick worked - the trimmer was right on minimum, the tuner went just to 104MHz and the AFC pulled in the 104.2MHz station too. Tweaking the RF amplifier at each end enhanced the AFC performance so that was good. Putting the can back on the tuner fortunately made little if any change. The scale was not quite right without the AFC on but not really far enough out to worry about.

[Mr 1936]

Hi

From your description, it seems to me that the Local Oscillator is not tuning correctly at the very bottom of the band (I doubt if the RF tuning would have such a marked effect).

This could be the AFC being over-enthusiatic, so as already suggested, switch that off and re-check behaviour.

Assuming it's not the AFC, and given that it's permeability tuned, I wonder if the core is getting right to the middle of the LO inductor (= maximum inductance) before the tuning pointer has quite reached the bottom of the band. You might be able to see this visually if you take screening lids(s) off. As you turn the tuning knob towards 88, the LO frequency will go down, stop changing (at around 89 on the dial) and then even go back up a little bit.

If this is the case, you may need to realign both the tuning string/pointer position AND the LO trimmer to get things working properly. Are there any signs that "someone" has been there before ?

[Pilot Mariner]

I have previously made sure the AFC switch is in the off position.

Looks like my next step is to get inside the tuner unit.

It looks like some capacitors have been previously replaced so someone has been here before, and the 1st IF (presumably) core on the tuner unit is suspiciously exposed by a few mm compared to my other HM2s. However it does peak at this setting.

Sadly work is getting in the way at the moment, so will report back later.

Many thanks