RM203p issue

[mu5tard]

Swap the relays out for a reliable brand such as Omron, the originals are carp.Your description suggests a relay is duff in one, or maybe two, possible modes. This is a quite “non-linear” Linear Amp so keep the input power a long way below the OEM specs. Plus fit a cooling fan, I fitted silent computer fan and controlled it by a thermistor (55C) . Then you stand a chance of a long happy relationship with the 203P, I’ve worked great dx on 10m CW -.-

[Mudslinger]

Thanks Mu5tard, this is meant to be my spare. The other one does indeed have a fan on the top and I run it at well below the maximum input, it's 12 years old now.

[NM1020]

You'd think that if it was just the relay sticking that giving it a 'clonk' on the top with the handle of a screwdriver or similar would un-stick it without having to switch it off and back on again. Switching it off and on would seem to indicate that there's a voltage from somewhere holding it in. Someone mentioned that it could be oscillating - I came across this once with one of the bigger RM amplifiers, a 400 I think. It was very intermittent and we never did get to the bottom of it, the chap sold it on in the end.

[Mudslinger]

I will update on this, I have replced the relays with better ones but haven't had the chance to try it yet.

[NM1020]

It'll be interesting to see if this cures the problem. It was suggested in a previous post that the relays used are not of a good quality, but then it could also be argued that there are hundreds, possibly even thousands of these little amplifiers out there running with their original relays without any problems. The thing that I can't work out is why the relay frees off when the unit is switched off, unless it's just the vibration of actually operating the switch which causes it to de-actuate. If the new relays cure the problem then that's all that matters, even if we don't fully understand the theory as to why this should be. These are good little amplifiers that probably more by luck than judgement are actually quite 'linear' in their operation and don't actually clip the waveform on AM/SSB, unlike most of the larger versions.

[Mudslinger]

Right I got my brother to try it and the problem still remains. It is allowing the radio to receive just not as well as it should be.

I am still suspicious that something in the setup is causing the issue, although with another identical 203p everything is fine.

[Mudslinger]

Another update. It is working... I have tried the amp of a totally different setup, including a mains PSU and inverted V and it works fine on that setup.

My brother was using it with a fairly long patch lead, and one of those light up Sirio 5000 antennas, so maybe one of those factors had something to do with it. But we tried two other KL203p's on his setup and they were both ok...

[pienari]

Oscilating issue some setup.
It can be fixed before it burn itself.
Remove original 4pcs RM3 fets and replace 6pcs IRF510.
Output is after modification 150w FM and never oscilate no more.

[Mudslinger]

Thanks for the info but it is still working fine.

I don't really want to fix it as it now appears ok...