Quad FM4 problems

[Mikeymoo]

Hello, I'm new to this site and very much a novice but was wondering if anyone could help with some issues I have with the above tuner not working? Purchased in the UK second hand some years ago and was working fine until the fuse blew. Took it to be repaired which wasn't too successful as after a short time, about half an hour the set never functioned. Have now moved to Portugal and keen to get it working. The fuse hasn't blown but after noticing smell and checked out the Rifa cap (which was cracked) I have replaced this. It was from this site that I viewed some similar problems in this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=95547

So have replaced cap, not with an original Rifa but was advised it is the same value as the Rifa, 0.047 uF but it doesn't have a reading as to the ohms. It should be 100 ohms. However the unit is still not powering up. Have checked with a continuity screw driver and it is live i.e fuse not blown. Any ideas as to what I could do to resolve problem(s) appreciated. Thanks

[SteveCG]

Mikeymoo,

When you say that you have checked with a continuity screwdriver and it is live, exactly how did you do this? Reason for asking is that I thought Portugal often used two pin mains sockets and so what is 'live' and what is 'neutral' depends upon which way around the plug is inserted into the mains socket. So are you quite sure the fuse is still intact? Using your screwdriver both ends of the fuse should be either live or not (ie neutral). What you should not have is one end of the fuse live and the other end not-live.

[nutteronthebus]

Hi I have posted the user manual and a doc of the power supply ( I do have the full PDF of the maintenance manual but is 5mb and can not post here PM me with an e-mail and I will send it )

Dave

[Mikeymoo]

Originally Posted by SteveCG

When you say that you have checked with a continuity screwdriver and it is live, exactly how did you do this?

Steve, I checked it after the power supply unit and assumed that the fuse hadn't blown. You have rightly observed that they do have the 2 pin plugs and can be plugged in either way but I thought this wouldn't make a difference? I.e. if the fuse was out it wouldn't be live?? How can I check the fuse? Visually it looks OK but is a very fine wire. Should I try another fuse? Thanks

[SteveCG]

Mikeymoo,

Am I correct in thinking you do not have test-meter (often called a multi-meter) and that you only have a neon continuity screwdriver? If you had a multi-meter then you could check the fuse for continuity directly.

For this check the screwdriver is fine. Allow me to explain. If you plug the tuner in to the mains and have it switched on AND the fuse is intact then:

EITHER the screwdriver will glow orange when you put it in contact first to one side of the fuse and then the other

OR it will not glow when you put it in contact first to one side of the fuse and then the other.

If the fuse has blown then you will find that the screwdriver glows when you put it in contact with one side, but it does not glow when put in contact with the other.

When the fuse is intact it acts like a short circuit so whatever voltage is on one side is on the other. However if it has blown then it is open circuit and acts as if the fuse was not present. Hence the different response to the screwdriver check.

This check is valid for whatever way around you have plugged the tuner into the two pin mains socket.

...hope that helps !

[julie_m]

Another way to test a fuse using a neon screwdriver:

1. Touch the tip of the screwdriver on something you know is live and make sure it glows.
2. Hold the fuse so that your finger is tounching the fuse, but the other end of the fuse is touching the clip of the screwdriver, so the fuse is completing the circuit back to your body.
3. Touch the known live terminal again with the screwdriver. If the fuse has blown, the neon will stay off.
4. If the neon lights at full brightness, the fuse is fine.

You can prove the screwdriver tests work using a brand new fuse and a fuse-sized piece of plastic, or a fuse covered in a layer of insulating tape. You can also test the fuse by substituting it in another appliance.

For sheer life-changing usefulness, though, even a cheap multimeter is an absolutely unregrettable purchase and you will forever be wondering how you managed to live without one so long. There is always something to be tested or measured!

[Mikeymoo]

Guys, many thanks for tips\advice. I do actually have a multi meter, purchased some years back at Maplins and it appears to work fine. However the instructions that came with it didn't give too much advice so have basically used it to check batteries. Furthermore the lid on the PSU did give a warning, high internal voltage, dangerous to unqualified persons! I do remember you mentioned Steve that the DC is high, around 500 or 600 volts so hence I haven't started probing around with the multi meter. I did try to check the continuity of the fuse with this, not in the unit but by itself but nothing appeared on multi meter? Does it have to be in the unit? Also will try the neon screw driver test but I think it'll be difficult to get the end of the screwdriver on either end of the fuse as is in the plastic cover underneath the plug. Many thanks for your patience and will hopefully use the process of elimination to sort out problem! Mikeymoo

[Mikeymoo]

Latest update, the fuse is good, did the test Steve and it appears to be working ok! What now? Time to cut loose with multi meter Thanks

[SteveCG]

...er Mikeymoo, no, I don't think I said the DC volts are high - if you examine the circuit diagram that Dave attached you can see that they are about 12 volts !

The only high voltages are those on the AC mains input to the transformer - so take care around it and its associated input components when the tuner is powered on.

I suggest your next move is to check that the 12 Volt DC rail is correct (this is the output of the 3 pin voltage regulator shown in the centre of the circuit diagram)

[Mikeymoo]

Steve, sorry about implicating you in the high voltage, this might have been when I purchased the replacement for the Rifa cap I think I saw that it was rated at 500 or 600 volts DC?? Anyway I have tried to get the reading as you suggested but have to discharge caps before taking reading as advised re. multi meter. How is this best achieved? Also I presume it is the 2 solder points that when viewed from above run between T9 and C6? Bit confusing as underneath on the PCB it has +12V and a printed line going to C6 and a + written next to it. Cheers

[Station X]

There is no need to discharge capacitors when taking voltage readings. You can only take voltage readings with the unit powered up, so the capacitors will recharge anyway.

You can check the 12V supply by connecting the meter leads to the ends of C6. Meter on DC volts, leads connected to COM and V sockets. 20V range if you have one.

Capacitors need to be discharged before taking resistance readings which must be done with the set powered down.

[Mikeymoo]

Graham, thanks for getting back to me, this is where I find the multi meter thing confusing. When I try to get a reading on DC manual it says nothing i.e 0.00 then when I try on DC auto it starts at high figure say 200mV then starts counting down and jumping all over the place, never staying on a set figure. Is there a problem with multi meter or is it the setting I'm using? Or is there no voltage going through this stage hence a problem in the DC stage? I had it on the ends of C6 with the unit upside down. Cheers

[Station X]

Try measuring the voltage of say a PP3 battery to see whether your meter is working correctly.

[Station X]

You can check out the fuse OFF/ON switch and mains transformer primary windings like this.

Set unplugged from the mains. Meter on lowest resistance range. Meter lead connected to the pins of what I assume is a two pin mains plug. When you switch the set on and off you should see the reading change from infinite to a low reading.

[Mikeymoo]

Graham, whats a PP3 battery? Cheers

[Station X]

A small 9 Volt battery. Possibly called something different in Portugal.

Might I suggest you google it!

[Mikeymoo]

OK, tried 9 volt batt and yes doesn't appear to read voltage correctly. Excuse me but hadn't heard a 9 volt battery called a PP3. Guess the meter isn't up to the job. Any other suggestions apart from getting new meter? Thanks

[Station X]

Check that:-

Battery in meter is healthy.

Battery being tested is healthy.

Meter leads are plugged into the correct sockets. Black (negative) lead goes into a socket which may be black and be labelled "COM". Red (positive) lead goes into a socket which may be red and be labelled "V" or "VOLTS". Check with the meter's manual. Don't use any socket marked "A" or "AMPS".

Meter leads aren't broken under the insulation.

Correct DC VOLTS range is selected. May be marked "DC" or "DCV" or have a straight line with a row of dots or dashes under it. Check the manual.

If all these conditions are met and you don't get a sensible reading then the meter has had it. Get a new one.

You could see whether the ohms/resistance ranges are working. Select a resistance range. Meter should read infinite may be shown as "OL" check the manual. Touch leads together. Meter should read low or zero resistance.

[Mikeymoo]

Graham, tried all of the above and made correct conx's re. leads etc. Battery is good but meter does have a low batt. sign if not ok. Leads don't appear to be broken so it seems meter not working. Will take same to a local electronics shop here in Porto and get final say on it and then purchase new one if needs be. Bit disappointing as my current model was capable of DC, AC volts and currents, resistance, diode test, capacitance and frequency. Any advice re. buying new one? Will keep it simple but digital probably easier to read than analogue for accuracy no doubt? Thanks for help. Mikeymoo

[Station X]

I'd get the best DMM you can afford. An analogue meter is likely to be expensive and if you went for a second hand one you'd have no idea whether it was working correctly.