RM203p issue

[Mudslinger]

A couple of years back I bought a new (or so I thought) RM KL203p from the bay of E.

I didn't actually manage to try it, and it ended up stuck under the bed until today.

It seems to have an issue, when transmitting it is putting put the correct amount of power but when turned to the linear on postion the radio that it is connected to stops receiving a signal. Totally deaf.

I am a bit annoyed that I didn't get to test it when it arrived, but for a couple of reasons it wasn't possible, as I could've just sent it back...

As I am now stuck with it, I may as well see if it can be fixed, what do we think is wrong? Switching relay?

[ch25]

Might be oscillating.
Is red led in front lit when deaf?

[Mudslinger]

I will need to check for sure as it was my brother testing it, but I think that it was on.

[NightProwler]

So it transmits ok but when you un-key the receive on the radio is deaf? Sounds like a sticky relay to me.

[NM1020]

It's the 203P, the 'P' meaning it's got a preamp fitted. These are a good little amp, but are well known for preamp failure causing the fault you describe. Receive preamp failure is usually caused by the antenna being left connected during a thunder storm. I've never seen the innards of one of these, but if it's the same as the bigger ones, then it's a single transistor and I seem to remember, although it's a long while ago, that I used something like a BC107 as a replacement to get them going again. It sounds like you possibly bought one that was returned to the supplier as faulty and when they tested it on a dummy load it would have seemed to work fine, so was sent out for sale again as fully functional - they wouldn't have noticed the preamp receive fault on a dummy load.

[Mudslinger]

So it transmits ok but when you un-key the receive on the radio is deaf? Sounds like a sticky relay to me.

Yes, and if you turn it off and back on it is back to normal until you transmit again.

[Mudslinger]

It's the 203P, the 'P' meaning it's got a preamp fitted. These are a good little amp, but are well known for preamp failure causing the fault you describe. Receive preamp failure is usually caused by the antenna being left connected during a thunder storm. I've never seen the innards of one of these, but if it's the same as the bigger ones, then it's a single transistor and I seem to remember, although it's a long while ago, that I used something like a BC107 as a replacement to get them going again. It sounds like you possibly bought one that was returned to the supplier as faulty and when they tested it on a dummy load it would have seemed to work fine, so was sent out for sale again as fully functional - they wouldn't have noticed the preamp receive fault on a dummy load.

It could be, but used on it's own the preamp seems to work ok.

[NM1020]

It could be, but used on it's own the preamp seems to work ok.

In that case, yes, it does sound like the relay is sticking, or possibly being held in by some voltage leaking from somewhere that's then being released when switched off and then back on again, but just guessing really without having the unit actually in front of me.

[Edd200sx]

Transistor voltage is leaking and they are not switching off

Could be bad fets.

[Mudslinger]

Thanks for the help guys, hopefully I will get it back this weekend and can get a look at it.

[Mudslinger]

I have just had a look at this, taken the covers off and there isn't anything obvious wrong. The Only "FET's" in the circuit according to the schematic are the MOS FETS, which I am pretty sure are ok as the full whack of power comes out no problem.

When the unit is dekeyed there is zero power coming out, but it is preventing any received signal passing through to the radio unless turned off and back on again.

I need to try it with a different radio and patch cord just to eliminate a quirk with the setup being the cause.

At very least it has to be worth a few quid spares or repairs due to the output MOSFETs being ok, especially if someone has an amp with them blown.

[NightProwler]

I still think the relay is sticking. I had the same problem in an RM plug in the wall amp years ago, Changed the RS relay and it worked again. If it's one of those relays that the cover comes off try spraying some contact cleaner in it.

[Mudslinger]

The relays appear sealed, I can get a pair of new ones for around £8 so may give that a try.

There is also chance that we may have some at work so will have a look there when I go back in next week.

[NightProwler]

I remember now there were two relays in mine. Mine was the homebase version. Two new relays and it worked again. Worth a try..

[Mudslinger]

Yes it has two.