Signal R535 scanner clicking

[flyM6RDP]

Hi,

I have an R535 scanner from Signal Communication Corps that clicks as it scans or searches.

The clicking is present with the antenna in or out and is in step with the scan or search speed, which makes me thinbk it might be processor noise being picked up.

Here is a short video:

Interestingly I took it down to a radio amateur/repairer and when he plugged it in: nada. Quiet as a mouse.

He thought it might be RF on the DC lead and suggested I try a 12v battery back at base, which I did and it made no difference.

Also, as I plugged in and out a pair of headphones, for a minute or two the noise disappeared, only to reappear.

A youtube friend said it might need "re-capping around the processor". Way out of my league.

Does anyone have any suggestions? Places I could look for a dodgy return earth joint? Simple things to try?

I've switch cleaned around the antenna & earphone sockets.

Thanks for reading. 73 Adam (M6RDP)

 

[Ubbe]

RF on the DC lead in a receiver?

This sounds as if the display updates are getting into the audio. Each time the display updates with new info the data is heard in the speaker.
Similar symptom that some SDS200 scanners have.

If you also brought your speaker setup to that radio amateur then it has to be something with the location of the receiver. Try and lift it or move to the side. Try turning the volume all the way down and all the way up. Are the data bursts also changing in volume?

Check if the receiver is grounded somewhere and if the speaker also has some type of ground, perhaps you have an amplified speaker as you are using the earphone jack. Connect a standard headphone or earphone and listen if the data burst are still heard, then it's probably something in the receiver that needs attention but should have been noted at that other test location.

/Ubbe

 

[flyM6RDP]

Hi Ubbe,

Thanks for all that information and your detailed and helpful reply.

Yes the clicking is apparent in the headphones.

And yes I am inclined to agree with you that there is something wrong internally in the radio. Simon Spiers on YouTube reckons it might be be a failed capacitor around the central processor. But that doesn't explain why there was no clicking at the test location.

I have taken the radio out of the shack with a portable 12-volt battery and out into the Open Air away from any electrical noise and yes the clicking is still there!

I think it might have to go back to the repair shop!

Here is a link to the video of the clicking

 

[Ubbe]

If the noise changed and dissapeared when you took it to the radio amateur, it must be some mechanical problem, some grounding that are not sufficient, exactly what the problem are in SDS200 scanners. Open up the receiver and loosen and then tighten each screw that looks as if it connects to ground. The earphone jack might sit on the same circuit board as the display so see to that it is properly grounded.

/Ubbe

 

[flyM6RDP]

Ubbe,

It's like having an online doctor haha

I have a few hours spare this evening so I will follow your suggestions regarding ground screws etc and report back

Thank you again, it is much appreciated. Adam

 

[flyM6RDP]

Hi Ubbe,

I spent a few hours yesterday evening tinkering around with the radio and tightening all the screws that I could. But unfortunately it has not made a difference.

I also carefully inspected both sides of the circuit board as best as I could with a magnifying glass to look for any cracks or problem areas but again everything looks good and clean and dry (not dry joints, I mean not damp from moisture!)

Anyway I will put any updates about the problem here on the forum.
73 Best wishes
Adam

 

[tvengr]

I have an R535 scanner from Signal Communication Corps that clicks as it scans or searches.

It sounds like a power supply decoupling issue. As suggested earlier, it could be a bad electrolytic capacitor. Considering its age and the problem being intermittent, I would also suspect a bad solder connection. Bad solder connections on circuit boards have a tendency to fail after about 10 to 15 years. If you have experience soldering, you could try reheating the connections on the capacitors. If that doesn't fix it, you probably have a bad decoupling capacitor.

 

[Ubbe]

I agree, decoupling capacitor that have dried up and the same voltage source used for both display and audio.
Strange though that it didn't show up at the place where the radio amateur would had been able to look at it.

/Ubbe

 

[flyM6RDP]

Tvengr, Ubbe

Thanks for this advice about capacitors. Since your messages I have had a look on YouTube at a great video about how to look for damaged ones and how to test them in circuit if there is no visible sign of damage. So I am trying to carefully dismantle the radio to have a good look at the ones around the processors.

The local radio fixer would I am sure be more than happy to look at it again for me when Im next down that part of the world. He is already looking at a very neglected and abused radio of mine which needs an awful lot of work and in the meantime I am quite happy to try to improve my own skills which are very sadly lacking! Impossible without the help of forums like this though and your assistance so thank you again.

It might take me some time but I will definitely report my findings here ASAP.

73 Adam

 

[tvengr]

Electrolytic capacitors usually don't show signs of damage unless they overheat. Usually, the electrolyte will dry up and the capacitor will decrease in value or completely open up.

 

[Ubbe]

You probably shouldn't look for bad caps around the processors. Look for them at the power supply components and any big el-lyt caps should be suspected. Sometimes they have bulged and are easily spotted but other times there are no visible signs and have to be measured on the voltages if they doesn't filter the DC voltage enough.

I usually test for bad caps just by bridging a cap with another good one, the same value or bigger, and see if that helps. I would focus around the area of the display. If the display have a cable that can be detached, then pull that and then listen if the data bursts dissapears.

/Ubbe

 

[flyM6RDP]

OK. Thanks. I will try the cable to the display.

The decoupling capacitors around the microprocessor are tiny and way beyond my skills to check or replace.

But the larger one around the the DC socket looks easier. This is the first photo.

While unplugging one of the cables I accidentally damaged a small ceramic capacitor! This is photo number 2. Will I need to replace it? It looks fairly straightforward.

 

[flyM6RDP]

I realise now the tiny ceramic capacitors around the the central processor are not decoupling capacitors are they...

There are some larger electrolytic capacitors on processor board. Photo attached.. that I could test and probably replace if careful.

Presumably I can't use my multimeter and I will need to buy a capacitance checker?

 

[tvengr]

If you have a scope, you can look for signals on the power supply bus. If a capacitor is good, you will usually see the same signal on both leads. If you use a capacitor checker, the capacitor must be removed from the circuit board to check it. Make sure that you replace an electrolytic capacitor in the same direction you removed it. Look for a ground stripe or plus sign when you remove it and replace it exactly the same way. If you put an electrolytic capacitor in backwards, they have a nasty habit of the electrolyte boiling, creating steam, and exploding. Using a multimeter on a capacitor, you should see a charging action. Set the meter to resistance on the highest scale with the minus lead to the minus side of the capacitor.

 

[Ubbe]

That ceramic cap are still functional, only cosmetic issue, so no need to replace. But bend both ceramics 45 degree out of the way from the connector to avoid any serious damages.

While you have the lid off, run the receiver and then poke on components and cables and wiggle the big el-lyt capacitors while listening for any changes in the sound. You can grab the chassi with two hands and twist it back and forth to check for any bad solderings.
Discharge yourself from any static buildups by holding to the chassi before touching any components.

/Ubbe

 

[flyM6RDP]

Thank you both.

It's good to know I haven't damaged it. But it was a timely warning of my inexperience! So I have now reassembled the radio. It still works, thank goodness! But still clicking........ I've wobbled the connectors to the display from the main PCB: no change. I don't have an oscilliscope or a capacitance meter. But I don't trust myself to solder inside.

I've done a few simple repairs to other Realistic radios: a stuck signal meter, a broken bulb, an EL backlight replacement, but this is beyond my skills I think.

However, I promise to post any updates when I have sent it off to the radio engineer later in the spring.

Thank you again to you both for your patience and support! 73 Adam