SWR Meter has an issue

[Spider255]

I have a CN620A 1.8 - 150MHz SWR/Power meter made by DAIWA its pretty old and has been my main meter for HF and low band VHF for many years.

It has developed a fault where its working intermittently, the power side of the meter works but the SWR side only works sometimes. I have checked the antenna coax leads and connectors so I know its not those causing the issue. The meter did take a knock a couple of years ago where it fell on to the floor but seemed to work fine after so I'm not sure whether that had anything to do with it or whether its just gone faulty recently. I haven't opened it up yet to see if I can spot anything, I'm hoping it would be a simple repair like a lose connection or something.

It is getting on a bit with age so possibly there is a component failing inside maybe and I was just wondering if anybody has one of these or might know what the fault could be so I have a better idea what to look for?

Thanks.

 

[K4EET]

I have a CN620A 1.8 - 150MHz SWR/Power meter made by DAIWA its pretty old and has been my main meter for HF and low band VHF for many years.

It has developed a fault where its working intermittently, the power side of the meter works but the SWR side only works sometimes. I have checked the antenna coax leads and connectors so I know its not those causing the issue. The meter did take a knock a couple of years ago where it fell on to the floor but seemed to work fine after so I'm not sure whether that had anything to do with it or whether its just gone faulty recently. I haven't opened it up yet to see if I can spot anything, I'm hoping it would be a simple repair like a lose connection or something.

It is getting on a bit with age so possibly there is a component failing inside maybe and I was just wondering if anybody has one of these or might know what the fault could be so I have a better idea what to look for?

Thanks.

Here is the schematic for your meter and the manual. I’ll digest the schematic to see where something may be intermittent.

 

[K4EET]

@Spider255, is the SWR intermittent on all power positions or just one (and which one)?

 

[K4EET]

@Spider255, when you say SWR is intermittent where the power needle (forward power) works fine but the SWR needle (reflected power) is intermittent, does the SWR needle stay at its resting position or is it “jumping around” while the transmitter is keyed? Does lightly tapping on the case when the SWR is intermittent resolve the problem? Any other information that you can provide that might help in troubleshooting the problem will be appreciated.

 

[K4EET]

Here are the datasheets for the diodes…

 

[Spider255]

@Spider255, when you say SWR is intermittent where the power needle (forward power) works fine but the SWR needle (reflected power) is intermittent, does the SWR needle stay at its resting position or is it “jumping around” while the transmitter is keyed? Does lightly tapping on the case when the SWR is intermittent resolve the problem? Any other information that you can provide that might help in troubleshooting the problem will be appreciated.

I've always used the the 20 watt and 200watt settings SWR will always be flat regardless of what band or frequency I use on it. Sometimes if I give it a shake or tapping the case SWR needle works as normal again but only for a short time. The needle doesn't look like its getting stuck as it will move freely when rotating the meter back and forth.

 

[K4EET]

Good morning @Spider255. First, I would hook up an HT on low power and test the 4 watt position. If that does the same thing, there are only a few parts that are common. The switch could be dirty (spray it with an electronics cleaner), a 2.2K ohm resistor, 10 pF variable capacitor, 10 pF capacitor, 100 pF capacitor, 5 uH choke, 18 ohm resistor, 1N60 diode, and a 0.01 uF capacitor. Look for a cold solder joint(s). The likelihood of an intermittent bad part is remote. I would really suspect switch S1 but that could potentially be cleared by changing switch settings a bunch of times. It is a simple circuit so it shouldn’t be too hard to troubleshoot. What test equipment do you have?

 

[Spider255]

Thanks I will open it up tomorrow and give the switch a clean with some isopropyl alcohol and see if that fixes it I will also look for any lose solder joints. Hopefully its just a dirty switch. The only test equipment I have is a NanoVNA.

 

[K4EET]

Thanks I will open it up tomorrow and give the switch a clean with some isopropyl alcohol and see if that fixes it I will also look for any lose solder joints. Hopefully its just a dirty switch. The only test equipment I have is a NanoVNA.

I would suggest using DeoxIT instead of isopropyl alcohol. Plastic and rubber parts can be damaged by isopropyl alcohol. I don’t have the UK Amazon link but here is the Stateside link for DeoxIT.

Amazon.com

 

[Spider255]

I cleaned the switch on the SWR meter and appears to be working again now... only time will tell but I've not had anymore issues with it so far.

 

[K4EET]

I cleaned the switch on the SWR meter and appears to be working again now... only time will tell but I've not had anymore issues with it so far.

Excellent! I hope it continues to work correctly. Gotta love easy solutions.