Roberts R727 low volume on am side

[pagu]

having just acquired a Roberts R727, I find the volume on the am side is on the low side,the fm side seems to be normal,was wondering if maybe one of the integrated circuits is faulty,or possible another component is off.

I am retired and am really just playing at the radio hobby with none or very little experience . Hopefully someone with the knowhow can point me in the right direction, (into the abyss).

thank you pagu

[Mark Hennessy]

Anything is possible, but I'd be surprised if it was a faulty IC, as the "AM" IC is used during FM operation, and it's unusual - though not impossible - for just a small part of an IC to fail.

I'd start by checking the alignment, but if you don't have the kit and experience, it might be better to leave it alone.

That said, the electrolytic capacitors used can be unreliable, so it would be worth looking at those. You can buy a tester on eBay for £10-20.

Have you got the right sort of DC voltages around IC2?

If you don't already have it, the schematic can be found here: http://www.vintage-radio.net/forum/showt...?t=98690#3

[Mike Watterson]

Check capacitors and maybe if the RF coils loose or been moved on ferrite rod, or if RF (not LO) AM trimmer has been moved, I'd not touch the IF or LO alignment.

[Refugee]

A visual examination of the slugs in the IF cans would be a good move. This may produce an answer especially if any trimmers have been "tinkered".

[pagu]

many thanks to all,I think I will go with a capacitor change for starters, it may help but should not cause any problems.

I do not fancy taking out the slugs,no guarantee they will go back to the rightful place.

The circuit diagram will help, if only to confirm voltages.

again many thanks,will report back.

pagu

[Mike Watterson]

No, don't touch the slugs!

But do check the position of the two coils on the ferrite rod as that makes a huge difference to AM only and they can come loose.

[Terry]

Check ... if RF (not LO) AM trimmer has been moved, I'd not touch the IF or LO alignment.

I'm not sure I understand the reason for ignoring the Local Oscillator coil - it is just as likely to have been interfered with as any other - and it is easy to reset using broadcast transmissions if an accurate signal generator is not to hand.

I'm quite sure that there are many on here who have quite happily - and accurately - carried out the RF alignment of many AM receivers - including those we built ourselves! - without access to a signal generator.

Of course, I admit there aren't as many AM signals around these days but those that are, as in the past, have a guaranteed accuracy far outstripping the accuracy of any signal generator we might have or desire! Of course, these days, I dare say there are a few synthesised generators sitting on enthusiasts shelves but I'm going back to the days when they didn't even exist! 

Even IF alignment should be simple - especially if only one circuit has been touched. FM alignment is, of course, an entirely different matter!

[Old Sparky]

It's possible that the AM Ceramic Filter (CF3) could be faulty. Years ago, when I repaired car radios for a living, I sometimes had to replace these filters. If you have an AM signal generator, it should be fairly easy to check for low gain at 468kHz.

[Refugee]

I do not fancy taking out the slugs,no guarantee they will go back to the rightful place.

You don't need to take the slugs out of the coils to see if they have been twiddled. The chips and cracks from the metal screwdriver will be obvious. It is extremely rare for a twiddledr to have the correct tools so a screwdriver gets rammed in there.

[Mike Watterson]

Check ... if RF (not LO) AM trimmer has been moved, I'd not touch the IF or LO alignment.

I'm not sure I understand the reason for ignoring the Local Oscillator coil - it is just as likely to have been interfered with as any other - and it is easy to reset using broadcast transmissions if an accurate signal generator is not to hand.

If the level is merely low, rather than stations off tune, there is no need to touch it. Also cores break easily, especially if one hasn't the right tools and experience freeing cores.
The OP didn't mention stations being off tune.
Yes, alignment using known stations is easy for the experienced.