Volume fault ? Trio 9R 59D

[Humptydumpty]

Back again for information on the Receiver no2 .

I switch the receiver on . Trio 9R59D
And as the set warms up, i turn the RF fully clockwise . [manual]
Then if i have to turn the AF anticlockwise fully to zero i can not turn the sound down or off from coming through the speaker . The I have to reduce the RF potentiometer .Question - is this is the correct way to do it ?
Could it be a fault with the AF potentiometer ?.

[JulietMike]

RF gain adjusts the sensitivity of the receiver.
AF gain adjusts the volume.

First check the connections to the potentiometer tags and look for a short between the inner conductors of the two screened cables.

John

[Humptydumpty]

Will do John . Let you know later on .. Its not working like the first Trio so i thought something was not right .

[Humptydumpty]

John i did checked it .. .The pot has 3 tags -top tag no1 is a white wire and earth to tag3. And the other white wire is to tag 2 and earth then going to tag 3 tag 3 is then going down to chassis for earth . They look just like the other set .I know a little about it because i changed the pot on the first one i had. It is wired the same way . How about if one part of the wiper in the pot is doing nothing ?. Only way out is to change the pot but need to be sure nothing else can cause this .

[JulietMike]

The connections look ok. If the pot is faulty you can use a multimeter to check that the resistance varies. I assume the knob is securely attached to the shaft.

John

[Humptydumpty]

Yes its working fine .That was the first thing i found when it came the knobs are not bog standard ,but like Cricklewood have in stock. But fixed on well now .Its like as if the first 1/2 of the pot is doing nothing till it gets half way .I have another to change it over but its a fiddley job to put in because the space is small and not a lot of wire to work with .I replaced both the screened cables on the first one this made it easy ..Phill sent me some . But i do have more now after i located it on fleabay . I will wait first and see if any members can come up with a soluton .

[Station X]

Originally Posted by Humptydumpty

I will wait first and see if any members can come up with a soluton .

Solutions aren't plucked out of thin air. You have to do some tests and post the results so that members can analyse them and make suggestions.

Is the pot the original 500kohm A law one?

Measure the resistance from the wiper, centre tag, of the pot to each end of the track, outer tags, in turn. While you're doing this rotate the knob to each extreme position in turn. If all is well the readings should be close to 500kohm at one extreme and close to zero at the other.

If with the knob in the centre position the reading is approximately 250kohm the pot has a linear law. If the reading differs significantly from this it has a logarithmic law.

Don't go off at a tangent and do something different. Do the tests suggested and post the results.

[JulietMike]

Trevor,

I suspect there is a crack in the track and the only reliable way to make a repair would be to replace the pot. With care you should be able to change it for a new one without replacing the screened cables - even if there is not much free cable or space. De-solder the cables before removing the pot.

John

[Humptydumpty]

John just had my analog meter on the pot . I find that as i turn it clockwise i have no movement on the meter needle ,thats till the pot is half way through its rotation.Shot or what .

[Station X]

Chances are it's shot, but you may need to switch ranges to get readings at both extremes.

[Humptydumpty]

Thanks Graham and John . . As my post above reads nothing moves on the meter till halfway through the pots movement . . I will try and do a full check Sunday and post the readings . It is the original 500k log pot ETNA make

[Station X]

What's the resistance from one end of the track to the other? If it's approximately 500kohm it won't have a crack in the track, but you may have wiper problems.

[Humptydumpty]

Graham - John i have 2 brand new pots just the same as the one in the set .I checked them and are all the same measurment on the meter with no lag as i turn the pot up .So for now i will muster up the courage to change it over for a new pot . Thanks both for your help once more . Regards Trev.

[David G4EBT]

It's a 500k logarithmic pot - not linear. Maybe it is faulty, but at half of its rotation, there will little change in resistance, (about 10% - 50K, then the other 90% - 450k would be in the other half of the rotation). That's quite unlike a 500K linear pot, which at the halfway point would read 250K. Before you change the pot, measure the resistance on a replacement one (470k log) at the halfway point and see what result you get.

You could do the same test on your existing pot - set the knob to the centre point of rotation, clip one Ohmmeter lead to the centre pin, then the other lead to each of the two pins on either side of the centre pin and note the two readings. If the result is roughly 50k and 450k, that suggests the pot is working correctly.

If you look at the graph here, you'll see how linear, log and reverse log pots behave.

http://www.geofex.com/Article_Folder...s/potscret.htm

As has been said several times, you won't make much headway by making assumptions and changing things on a whim hoping that you might get lucky.

[Humptydumpty]

David check on the pot shows no readings from tag 1 and tag 2 on or off . Reads ok on tags 2 and 3 thats with pot turned up or down .What ohms should i find .

[Station X]

Originally Posted by Station X

What's the resistance from one end of the track to the other? If it's approximately 500kohm it won't have a crack in the track, but you may have wiper problems.

What's the resistance between the two outer tags. We need an actual reading ie open circuit, short circuit or n ohms.

[Humptydumpty]

Graham no reading from outer tags 1 and 3

[David G4EBT]

If there's a break in the track, as shown in the diagram below, there will be an open circuit between tags 1 & 3, (instead of 500k Ohms). If the break is between tags 1 & 2 (2 being the wiper), there will be an open circuit between those tags. Between tags 2 & 3, there will be a resistance which will vary as the potentiometer is rotated (leftwards in the diagram), until the wiper of the pot passes over the break, when the meter will show an open circuit.

[Station X]

Originally Posted by Humptydumpty

Graham no reading from outer tags 1 and 3

In an earlier post you said that you were using an analogue meter, so I assume that by "no reading" you mean that the needle is sat at the left hand end of the scale indicating open circuit?

What meter range are you using? For example ohms X100.

What's the max resistance you measure between tags 2 and 3 before the reading goes to open circuit.

As I've said before we need values.

I get a reading on my kitchen scales. Meaningless.
I get a reading of 10 on my kitchen scales. Meaningless.
I get a reading of 10 ounces on my kitchen scales. Meaningful.

[Humptydumpty]

I dont use kitchen scales to take readings from the electronics . .

This first picture is testing a good known pot . readings show 500 with it turned down .
Second picture with pot turned up readings show500 .
Next is the old pot in the set no readings up or down .