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Old 15th Jun 2019, 11:16 am   #1
andrewgm
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Default Signal Communications Corp R535 Receiver

Hello everyone - new to the forum and just joined.
My electronics experience and knowledge is quite low level compared to the majority or members here so apologies in advance !

My problem is I have a beautiful and very good Signal R535 ( as it's called ) dedicated to monitoring of Civil and Military Airband frequencies. The beauty of it lies in its simplicity of function and layout internally. It's not riddled with dials, knobs and mysterious displays that look like it belongs in a plane itself.
Anyway its performance is still sensational compared even to some more modern offerings.

Getting to the point then. It runs on a quite normal 12V DC feed and inside the case is a 1000uf 16v electrolytic and UN4002 diode across the +/ve and -/ve - the schematic supports this.

I now regrettably decided to change the cap to a low ESR Panasonic FC and UF4002 diode while I was in. It all went well, I don't remember snapping anything, something falling out unexpectedly, dropping any solder inside or any moments when I thought "Oh God"

I put it all back together, powered her up and the display was fine, the functions were fine, squelch functioning, noise was the same - no problems.
Except I've got FM radio transmissions all over it and bizarrely no Airband comms at all.

I put another radio in its place and it worked fine. I even put back the old bits and of course that didn't help.

I'm not the kid waving a hand held round in the air at an airport but am quite serious about the hobby as I enjoy it very much. My system comprises of a copper J pole at height and cut for civil Airband frequencies, use LMR400 coax at under 10 metres in length, have a dedicated low noise power supply, passband filter made for airband listening and have an RF filter on the 12v power supply line to the R535 itself. Pilot transmissions are like DAB radio and the tower transmission is first class.

I say is......it was !! The FM breakthrough strength at the moment gets through the passband filter it seems !

So, anyone any ideas on what on earth I've done to it!? I've done something for sure but I'm just not clever enough.

Many thanks, Andrew.
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Old 15th Jun 2019, 1:30 pm   #2
Hans PE1KWH
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Default Re: Signal Communications Corp R535 Receiver

FM breakthrough IF is recognized by being untunable, So changing the dial does not alter the received station.
This can happen after you remove shielding cans or break shielding cans solderings.

If it is changing with the dial your oscillator runs at some other frequency.
As this is a cpu pll controlled set it means the pll can not lock.
On the boards a pll chip is located.
Maybe some solder fallen in or a soldering broken in that part ?

If you're not capable of measuring frequencies inside that radio you best find someone who can otherwise use the service manual ( https://www.pe2kmv.nl/wp/en/rx-only-...corp-r-535-uk/ ) to measure and find that fault.

Don't forget it is older equipment now and problems will arise.
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Old 15th Jun 2019, 4:23 pm   #3
andrewgm
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Default Re: Signal Communications Corp R535 Receiver

Thank you very much for this very thoughtful reply.
I will now try and identify the chip from the schema and drawings and look for my errors....as it can only be me to blame

Many many thanks

Andrew
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Old 16th Jun 2019, 1:56 am   #4
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Default Re: Signal Communications Corp R535 Receiver

Hi Andrew, and welcome to the forum. I too have a Signal R535 and it does look like you are receiving an image from the FM broadcast band. Assuming the IF is 10.7MHz (I can't be sure without looking at the circuit diagram) and you are monitoring Newcastle on 124.375, this should give a local oscillator frequency of 113.675MHz (124.375MHz-10.7MHz). If you have another receiver such as a scanner, try tuning it to this frequency, and if the local oscillator PLL is locked and functioning correctly, it should be possible to pick this up if held near the R535. If not there is something wrong with the oscillator.
Alan.
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Old 16th Jun 2019, 2:25 am   #5
andrewgm
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Default Re: Signal Communications Corp R535 Receiver

Oh right...I'll give that a go.
I have hand held Yupiteru I guess will be useful for that.
It's such a worry now - it's my price and joy tbh.
My main monitoring frequency is precisely the one you mention - how did you know that ?
What will I hear if the oscillator is locked or not locked ?

Thanks for the idea.

Andrew
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Old 16th Jun 2019, 10:02 am   #6
Jon_G4MDC
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Default Re: Signal Communications Corp R535 Receiver

I see I posted a link which has already been given to the service manual - now removed.

It is clear from the schematic that the IF is 21.4MHz not 10.7MHz. It is most likely that the PLL is unlocked.
That is a CX7925B which appears to be from Sony.

Local oscillator runs on high side so 124.375+21.4 = 145.775MHz is where you should look.

Last edited by Jon_G4MDC; 16th Jun 2019 at 10:17 am.
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Old 18th Jun 2019, 8:19 pm   #7
andrewgm
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Default Re: Signal Communications Corp R535 Receiver

Well you were right Jon_G4MDC ....144.845 is precisely where my other scanner matched it.

That's great and thank you for pointing me in the right direction of tuning.
What does it mean then ?
If the PLL is unlocked can it be re locked or fixed ?
I've already ordered another Sony CX7925B in the hope it can somehow
be replaced.
Maybe it's easy - maybe it's terminal beyond repair

What I do know is I'm really grateful for all of you who have searched your knowledge for me.
I just pop up from nowhere and ask for help and I can't help in return sadly.
I've bee working away too and couldn't acknowledge either - sorry

Andrew
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Old 20th Jun 2019, 9:37 pm   #8
Biggles
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Default Re: Signal Communications Corp R535 Receiver

It could be that the reference oscillator has stopped working (which may of course be due to the PLL chip being faulty). Again, without reference to the manual, I can't tell you what the frequency is but it typically is something like 6.4MHz. Without this crystal oscillator functioning, it will be impossible for the PLL to lock. It may be worth using the same technique to try and pick up the reference oscillator signal with another scanner held close to the 535. Look for solder splashes and excess solder shorting tracks on the pcb. Use a good magnifying glass and you may be lucky and find a problem. A good visual inspection is well worth being the first step with any fault in my experience.
Alan.
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Old 21st Jun 2019, 1:16 am   #9
andrewgm
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Default Re: Signal Communications Corp R535 Receiver

Thanks Alan
It's got 12.800mhz on the side of the crystal oscillator - precisely double your own guess - I think that's significant in itself.
Should I also get one of those too ?
Y'know I've racked my brains going through the video in my head of the moment I did the work on it. It was a fiddly little job with not much room and it's possible my ' non iron ' hand was leaning on certain components. I was holding the wires to solder them back to the tags of the 12v socket. Have I created a dry joint, or disturbed an important one perhaps ? Tempted to get my thin tip on the station and ' re do ' the lot frankly.
I'm certainly capable of it.
I can even replace the pll chip and the crystal myself......I've done several TDA 1541 S1 and S2 Dac chip transplants over the years and don't fear the task. This main board is a really traditional all solder trace type whereas the above jobs were done on thin pcb tracks.
I've found a 13mhz HC49 Crystal already but I need to do some more digging asap.
Oh...and the crystal and pll are right next to where I was working...mmmm
It's making some sense now...
Thanks for your input - really much appreciated
Andrew
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Old 21st Jun 2019, 10:04 am   #10
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Default Re: Signal Communications Corp R535 Receiver

Hi Andrew, we like this sort of thing!
Biggles has a good point to look for PLL reference frequency - definitely before touching the CX7925B!! Absolute last resort there.

The reference frequency comes from a crystal - in an oval metal can and with part reference Y2. I have highlighted the location on the main RF board here.
Mostly these have the frequency stamped on the can and are easy to read. See if you can pick up that frequency on another receiver.
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Old 21st Jun 2019, 10:10 am   #11
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Default Re: Signal Communications Corp R535 Receiver

The time I have ordered chips only to find it is not that. Could even be the crystal itself or dry jointed.

You need a head magnifier though and to know what you are looking for.
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Old 21st Jun 2019, 1:56 pm   #12
andrewgm
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Default Re: Signal Communications Corp R535 Receiver

Quote:
Originally Posted by Jon_G4MDC View Post
Hi Andrew, we like this sort of thing!
Biggles has a good point to look for PLL reference frequency - definitely before touching the CX7925B!! Absolute last resort there.

The reference frequency comes from a crystal - in an oval metal can and with part reference Y2. I have highlighted the location on the main RF board here.
Mostly these have the frequency stamped on the can and are easy to read. See if you can pick up that frequency on another receiver.
...and I thought I was being a pain in the a.. !
Thank you for your encouragement...I'll do what you say and report back...
Quote:
Originally Posted by HamishBoxer View Post
The time I have ordered chips only to find it is not that. Could even be the crystal itself or dry jointed.

You need a head magnifier though and to know what you are looking for.
I'll buy one, and I'm beginning to understand the schema and the board itself now.

Thanks for your input

Andrew
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Old 21st Jun 2019, 2:42 pm   #13
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Default Re: Signal Communications Corp R535 Receiver

I was just looking at it some more. I have found the tuning line which the PLL uses to adjust the frequency of the local oscillator and all the signal frequency tuned circuits.

If you have a Volt meter it could be interesting to see what that line is doing. At the low frequency end of the band it should have relatively low Voltage increasing the higher in frequency you tune. If that line is stuck with Voltage high or low not moving with tuning then it is fairly sure the PLL is out of lock.

Do you have a Voltmeter of any kind?
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Old 21st Jun 2019, 6:52 pm   #14
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Default Re: Signal Communications Corp R535 Receiver

When you picked up the 145MHz-ish local oscillator signal as per post #7, did you try changing the 535 receiver's channel frequency, say, by 100KHz or so and see whether the local oscillator signal shifted by 100KHz too? If it did then it's a sure sign that the PLL is locked and functional and you can direct your attention to some other fault. It may save you a bit of work, and chip changing. I have found the circuit diagram for the receiver but my copy is not very clear.
Alan.
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Old 23rd Jun 2019, 10:49 pm   #15
andrewgm
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Default Re: Signal Communications Corp R535 Receiver

Quote:
Originally Posted by Jon_G4MDC View Post
I was just looking at it some more. I have found the tuning line which the PLL uses to adjust the frequency of the local oscillator and all the signal frequency tuned circuits.

If you have a Volt meter it could be interesting to see what that line is doing. At the low frequency end of the band it should have relatively low Voltage increasing the higher in frequency you tune. If that line is stuck with Voltage high or low not moving with tuning then it is fairly sure the PLL is out of lock.

Do you have a Voltmeter of any kind?
Sorry for the delay - what with work, the kids and the wife the ' me time ' gets less and less.

I do have a volt meter but it's pretty basic.
I can use it properly however and will give it a go.

The good news is the pressure is off and the feeling of grief and loss is gone.
I bought another R535.....and an R532 which I've always wanted to try.
If only for it's extra sensitivity.
So, now more than happy to completely blow up the old R535
Which I won't of course.

Let me know what to do...and I hope I understand it

Many thanks

Andrew

Quote:
Originally Posted by Biggles View Post
When you picked up the 145MHz-ish local oscillator signal as per post #7, did you try changing the 535 receiver's channel frequency, say, by 100KHz or so and see whether the local oscillator signal shifted by 100KHz too? If it did then it's a sure sign that the PLL is locked and functional and you can direct your attention to some other fault. It may save you a bit of work, and chip changing. I have found the circuit diagram for the receiver but my copy is not very clear.
Alan.
That's interesting Alan and a simple test.
I'll certainly try that and report back tomorrow.

Like previously posted I managed to find another ( the same model ) which will never have the lid removed unless the batteries need changing !
Lesson learned

Thanks for the idea though - I'll do it

Andrew
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Old 25th Jun 2019, 8:28 pm   #16
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Default Re: Signal Communications Corp R535 Receiver

Progress.
With a bit of luck it'll be in the hands of a genius and long standing member of this forum sometime tomorrow.
He has a scope too, knows precisely what he's doing ( like you guys ) and will find the fault with his understanding in these matters - I know it.
I'll report back his findings as soon as he's had time to take a look.

Apologies for my lack of confidence in having a go too - it's sadly beyond me frankly.

Andrew
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Old 25th Jun 2019, 9:30 pm   #17
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Default Re: Signal Communications Corp R535 Receiver

That's fair enough!

Pity that 210miles or so puts that interesting fault out of range. We hope to hear about the resolution.

Have never come across these sets before so it has been interesting.
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Old 25th Jun 2019, 11:46 pm   #18
andrewgm
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Default Re: Signal Communications Corp R535 Receiver

I WILL absolutely report back to you - I owe you that.

There's a sense of calm around the place since I found another one though !
My error did disturb me - more than I care to admit particularly as a supposed grown adult.
A bit of a game changer - to accept the limitations of my ability with regard
electronics.
Sure, I can can solder very nicely, put audio grade mono bloc power amplifiers together, add additional linear power supplies to the digital and analogue sections of CD players and the like.
However, this has nothing to do with sensitive and reasonably old - ish radios / receivers etc nor the logic and mathematics behind real electronics.

That part is for you guys who were paying attention at school while I was dreaming of girls.
I regret that now particularly after once previously dormant parts of my brain are now fully engaged with the hobby.....whilst I am tempted to laugh it's really very painful.

Anyway enough of the bleating - if this man can't find the fault never mind fix it I'll attempt to east my own head live on TV - you'll just know it's me

I'll be back......

Andrew
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