Formac 120 no output.

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original45
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Formac 120 no output.

Post by original45 » 23 Jun 2018, 12:52

Got a formac 120 am fm apparently used to give a10 watt output.

Had a quick look inside before powering up ,nothing noted as burnt discoloured so on.

Turns on fine,a.m f.m switch needs contact cleaner but everything else seems to work ok.

Rx signal seems fine as is selector but on tx yes you might have guessed the needle heads the wrong way and doesn't budge.same on am fm

Any ideas before I consider if it's worth sending to be fixed.

Shame as it is in nice condition with user manual and original mic.

Thank you

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Mitch
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Re: Formac 120 no output.

Post by Mitch » 23 Jun 2018, 13:07

Diode D13 on the supply to the finals will have gone open circuit, it's one of their week points. replace with at least a 2 amp rated diode (noting polarity). It's just in front of the screening for the output, it's red and roundish usually. It's easy to check if you've got a voltmeter the diode will have 12v on one side and the other will have 0v when keying up. You should be able to hear it on a nearby radio as well.
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original45
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Re: Formac 120 no output.

Post by original45 » 23 Jun 2018, 13:41

Mitch thank you, I'm not technical but have a multi tester and I will give it a test latter as I just disappointedly put it away.

Really is in nice condition too with bracket and no damage or scratches.

If it's something I can do myself that would be great,I will test it and see.

Could you explain to me please where to place the test prongs for a diode as I really have no idea.
But will Google it also.

original45
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Re: Formac 120 no output.

Post by original45 » 23 Jun 2018, 17:32

I believe I found the diode. Its red about 15 mm long with 100ohm on it.

I tested it correctly as minus was marked on board and could find no voltage on mic key up.0.

So I moved switches on front.am FM switch and keyed up bingo .needle shot over .

Re connected sleeker wires yellow to + green to - oposit to how it was because I found ref on net to yellow light colours being pluss and darks and green being -.


Anyway,went on air am and FM and found a local lad who could follow me on both.seems to work well so far however I think the am FM switch is dirty because it doesn't select and always give RX volume and crackles.

So whipped case of and applied contact cleaner.worked switches few times now they feel silky smooth.

Need to leave it 24 hrs for electrical contact cleaner to evaporate.

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Mitch
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Re: Formac 120 no output.

Post by Mitch » 23 Jun 2018, 20:00

If it's the AM/FM switch it could be replaced. It's still worth replacing the diode tho' imho, here's a pic of mine from my Formac 88 for reference, note it's already been changed :)
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original45
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Re: Formac 120 no output.

Post by original45 » 23 Jun 2018, 20:13

Thanks Mitch, I was testing wrong diode lol. I'm not technical not h but now I see it I can test tomorrow.
Just to make sure.

It's possible it may have been the ptt switch too as all switches were rough until cleaned and seems strange that whilst mic was keyed up for several seconds it kicked in .
Weird.
Either that or a part it faulty.

I don't sell what I buy Mitch ,so if it's not right it will more than likely go to Nick to sort.
But it already owes me £20.

I saw you post on audio vr on the board by mic plug,will clean that tomorrow and increase it slightly by anti clockwise tweek .

Appreciate the help mate.

original45
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Re: Formac 120 no output.

Post by original45 » 24 Jun 2018, 19:31

A.m f m switch is now faultless,selects sweet and no loss of rx audio to speeker.

Seems to have a slight occasional loss of tx audio , I tested it myself and found it occasionally crackles and looses audio although needle is still in same position.

I have sprayed both sides of plug with electrical contact cleaner and cleaned with cotton buds around all pins and inside the female plug as best I can.

Didn't feel like a broken wire when moving mic plug and wire and didn't loose audio at all when mic plug was slightly pulled out so just guessing it's dirty or worn pin or female contacts .

Will try again tomoz.

Just a quick question on fm deviation vr if I turn it up slightly that only adjusts audio tx volume as such and doesn't make it sound off frequency does it ? .

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Mitch
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Re: Formac 120 no output.

Post by Mitch » 01 Jul 2018, 19:52

original45 wrote:
24 Jun 2018, 19:31
...
Just a quick question on fm deviation vr if I turn it up slightly that only adjusts audio tx volume as such and doesn't make it sound off frequency does it ?
It only adjusts outgoing TX audio, and not by much usually, it won't spoil anything else. You'll need to add a 68pf ceramic cap to the crystal board trimmer to shift the frequency for UK, if it hasn't been done already. I also changed the output transistor on mine, from a 2SC1969 to a 2SC1307, much better suited imho, no power fade on long overs! Worth doing if you can find one. I plan on fitting a legal board one day too, though I don't think the cost will be reflected in radio's value, but just easier and more conveneint to use.

I like Formac's tbh, I think they're a crackin' little radio, one of my faves, that's why I got one. Great for mobile and homebase alike.
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Re: Formac 120 no output.

Post by Kaliphan » 02 Jul 2018, 08:31

Think of your signal as a bloke.

The receiver filtering is a narrow door (unless you've got a Fidelity 1000 that has extra wide filters for HiFi performance).

If the bloke is thin (correct deviation) he'll fit through easily without having to be squashed, if he's excessively fat (overdeviation) then he won't and he'll be distorted as he tries to get through.

It's even worse for him if he tries to walk through the door and is off centre (off frequency) because more of him will hit the door frame and he'll make some terrible noises as he gives himself a black eye.

Formacs are a fun little radio but the FM on them is done badly (they FM the 10.695MHz carrier crystal) and doesn't usually give enough deviation, it's common to find they still transmit on Mid at the same time as you're on Lo or Hi because of the way the crystal switching is done (try it, put it on 20 Hi and listen on another radio on 20 Mid)

original45
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Re: Formac 120 no output.

Post by original45 » 02 Jul 2018, 08:47

Mitch wrote:
01 Jul 2018, 19:52
original45 wrote:
24 Jun 2018, 19:31
...
Just a quick question on fm deviation vr if I turn it up slightly that only adjusts audio tx volume as such and doesn't make it sound off frequency does it ?
It only adjusts outgoing TX audio, and not by much usually, it won't spoil anything else. You'll need to add a 68pf ceramic cap to the crystal board trimmer to shift the frequency for UK, if it hasn't been done already. I also changed the output transistor on mine, from a 2SC1969 to a 2SC1307, much better suited imho, no power fade on long overs! Worth doing if you can find one. I plan on fitting a legal board one day too, though I don't think the cost will be reflected in radio's value, but just easier and more conveneint to use.

I like Formac's tbh, I think they're a crackin' little radio, one of my faves, that's why I got one. Great for mobile and homebase alike.
Thanks Mitch.
After talking to Nick it's clear that the radio is still as it was from factory. It's 4kc too high on mid switch for UK fm if I have that correct.

He explained the cap needid too.
Yes I like the radio ,nothing special but still I like it and it is pretty nice condition .
I'm not sure I have the confidence to solder the cap and even less to do little swap of that bit at the back so I will be sending it to Nick when I have found a suitable box .

Why is the mid switch for fm 4kc high ,is that a standard frequency for USA or some other reason ??.
I too wondered if it would be best left as is on the mid fm all be it too high for UK use and add the uk fm board but again may just be ott.
And detract too much from originality, the cap I imagine is a simple removable mod if chosen to do so.

I believe it pushes 10 watts too,so wonder if a variable switch would be wise or just a smaller switch on rear to cut power to 3 watts so it could be used with a 203 if required.

Thank you again all.

mrpsychopath
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Re: Formac 120 no output.

Post by mrpsychopath » 02 Jul 2018, 10:29

Ask Nick to fit a dropper switch, to drop radio freqency to uk, he did it to a few am fm radios or me. That way the radios is standard fcc until you flick the switch.
Kill em all and let god sort them out.

original45
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Re: Formac 120 no output.

Post by original45 » 02 Jul 2018, 11:54

mrpsychopath wrote:
02 Jul 2018, 10:29
Ask Nick to fit a dropper switch, to drop radio freqency to uk, he did it to a few am fm radios or me. That way the radios is standard fcc until you flick the switch.
Sounds a reasonable idea. Does anyone actually still use the frequency on fm that these formacs are set up for?

Why is it 4kc higher than uk fm ?.

Yes the switch idea I like. Get both then in case the original frequency are still used elsewhere.
Cheers for that

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Re: Formac 120 no output.

Post by mrpsychopath » 02 Jul 2018, 14:11

It still leaves the radio with standard channel setup and you can drop onto uk at flick of a switch. Or go whole hog and fit full uk 40, you will have a complete band then with correctly numbered channels, if a pic is available for the radio. If not a dropper is ideal. Use the useless pa switch.
Kill em all and let god sort them out.

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