Questions about Philips PM5133 audio function generator

auato · **Joined:** Nov Tue 09, 2010 11:22 pm **Posts:** 11

Hi all.
I need your help to understand if my unit Philips PM5133 function generator is faulted. This unit seems ro run good (attenuator is OK, level waveforms are OK, speep OK and so on) but I do not able to reach maximum frequency of 2MHz. The maxumum frequency in normal mode is 390KHz (see vieo below)
Another strage matter: on the Service Manual I see two frequency potentiometers START & STOP with fine and coarse functionality

...and also looking the front panel two pots seem coaxial type but only the fine one turn itself while the coarse seems locked. Can any PM5133's owner inform me about these potentiometers? (if they are coaxial or not)

http://youtu.be/rNUEUjtAwlM

Thanks

auato · **Joined:** Nov Tue 09, 2010 11:22 pm **Posts:** 11

Hello.
Just an update: this afternoon I tried to go deep into the matter and I undestood that two coax post have the coarse section totally locked. Not succesful to unlock them and I do not know why they are so locked. It's a very strange matter... I have already tried with WD40 spray.
However, if I replace the coarse section by another 4.7K trimmer and the frequency reaches 2MHz. Now I'm worried to find two 4.7K linerar coax potentiometers. These pots seem too hard to find.
The genuine pots are made by Ruwido. Nothing on eBay. Please, any tip where to buy these ?

http://youtu.be/YM1NsKufeZ8

Than you

Mikeinkcmo · **Joined:** Oct Sun 15, 2006 12:57 pm **Posts:** 3174

I would think major suppliers in EU would have dual section potentiometers. You may not be able to find a 4K7 but a dual 5K would probably be fine.

A quick look here and there are a couple big US suppliers have dual section types.

mescalero · **Posted:** Mar Sun 18, 2012 4:10 pm

Because the pots that you have are locked up, you have nothing to lose if you try to take them apart. I do not know if you have pots that may be easily disassembled or not. Many pots have little metal tabs that may be bent to remove the back cover. If they are frozen inside it may be best to replace them even if you can (open and) repair them.
I agree that a dual 5K should work. If you can find it, a "linear taper" is the proper type to replace it with. You may only be able to find "audio taper" and those will work well but the adjustment will change its rate as you turn them. Good luck, and, great troubleshooting job. I believe that you have found the source of trouble.

auato · **Joined:** Nov Tue 09, 2010 11:22 pm **Posts:** 11

mescalero wrote:

Because the pots that you have are locked up, you have nothing to lose if you try to take them apart. I do not know if you have pots that may be easily disassembled or not. Many pots have little metal tabs that may be bent to remove the back cover. If they are frozen inside it may be best to replace them even if you can (open and) repair them.
I agree that a dual 5K should work. If you can find it, a "linear taper" is the proper type to replace it with. You may only be able to find "audio taper" and those will work well but the adjustment will change its rate as you turn them. Good luck, and, great troubleshooting job. I believe that you have found the source of trouble.

@mescalero thanks for the encouragement. Unfortunately it is riveted. I try to open it but I'm sure to break it. I also think 5K is fine but where do I buy these stacked pots? Only found 500K or 250K audio tapers :cry:

Ciro

Questions about Philips PM5133 audio function generator

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