Rotel RVC 240 S meter reading too high

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HeliJimbo
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Rotel RVC 240 S meter reading too high

Post by HeliJimbo »

Hi all,

I'm after some advice.

I have a Rotel 240 that I've just restored: recapped, LEDs swapped out for the blown bulbs, full tune and alignment and all went well.

The only issue I'm having is with the S meter on receive.

It's showing a constant S9 with an antenna even when calibrated to receive S9 with 50uV into 50 Ohms.

Even with a dummy load it's showing S2 so I'm not sure what's going on.

With another radio, the noise is about S2 so I'm pretty sure it's the Rotel behaving a little strange.

Does this ring any bells to anyone?

Many thanks.

James
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Buick Mackane
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Re: Rotel RVC 240 S meter reading too high

Post by Buick Mackane »

HeliJimbo wrote: 11 Feb 2022, 19:07

It's showing a constant S9 with an antenna even when calibrated to receive S9 with 50uV into 50 Ohms.

Welcome james.

I think its 100uV for S9
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HeliJimbo
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Re: Rotel RVC 240 S meter reading too high

Post by HeliJimbo »

Hi,

I thought me saying 50uV would get some kind of response.

My understanding is it''s 100uV but it's 50uV into a 50 ohm load? Also a rig I checked the other day that was fresh out of alignment, that meter read S9 at 50uV. Maybe my understanding is wrong.

Even so, the needle is still reading far too high with it set at 100 uv.

There's not a lot between 50 and 100 on my meter so I'm a little confused.
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Re: Rotel RVC 240 S meter reading too high

Post by Buick Mackane »

Your meter is reading to high because you've set the meter to read S-9 For 50uV, It should read S-9 for 100uV
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HeliJimbo
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Re: Rotel RVC 240 S meter reading too high

Post by HeliJimbo »

I've just set it to 100uV and it's still the same.

Even with a dummy load it's reading S2.

A little odd.
ChubbyChops
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Re: Rotel RVC 240 S meter reading too high

Post by ChubbyChops »

RV3 should be 20k
R47 should be 820R
C76 should be 10n
https://www.blunham.com/Misc/CB/PDFs/Rotel240etc.pdf
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Re: Rotel RVC 240 S meter reading too high

Post by The Collector »

My expert advice would be to just turn the meter trimmer down a bit.

Who says I know nothing about electronics??? ;)
HeliJimbo
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Re: Rotel RVC 240 S meter reading too high

Post by HeliJimbo »

I've finally got around to borrowing another set with the same chassis and have been probing around with my scope for ages.

While comparing the Harrier CBX, it seems this doesn't have capacitor C69, the emitter bypass capacitor for Q10

I remember a few months ago while recapping my Rotel, that I thought I lost C69 so found the value for it and then replaced it. I never did find the missing one.

When I remove the emitter bypass cap, the problem of it reading S2 with a dummy load in, goes back to zero.

When I add the cap to the Harrier, then exactly the same symptoms are there which I have been experiencing with the Rotel.

So, does anyone else have one of these chassis with C69 in place or no C69?

I'm wondering if I've been chasing a fault that I created, but then again, C69 is on the diagram.

Does anyone have any thoughts on this?

Many thanks.

James
HeliJimbo
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Re: Rotel RVC 240 S meter reading too high

Post by HeliJimbo »

I have finally confirmed now with 2 additional chassis that C69 should never have been there, even though it's in the diagram, albeit with no value.

Mystery solved!
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