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Hi All Need some help Thought my RM HLA300 low power output was due to one or more of the sd1446's going bad but now i'm not so sure. Looked at the waveform with my oscilloscope on the base of each SD1446 transistor on transmit cw keydown. Two of the transistors had a fairly pure...

Solved Ok looks like I found the problem with some help from Andrew at RM (nice chap) At some stage someone has replaced one of the SD1446 transistors This is obviously a different batch from the rest and has a different gain letter. I didnt spot this but Andrew did from a picture We're...

R37 is part of the base bias / feedback circuit for one of the sd1446 RF power transistors. It connects via a capacitor from the collector to the base then another resistor connects from the base to ground. I've checked all the components around the transistors and they all seem to check ok.

Hi Thanks for the response Ok have found someting else I did a cw keydown test about 7w in and 100 watts out The sd1446's started getting warm to the touch but not hot After about 10 seconds R37 was visibly getting very hot and started to smell So need to work out why r37 is passing...

I replaced the wire wounds with carbon and there is a slight improvement but not much. I've already lifted the base on each transistor and the b-c and b-e junctions pass the forward and reverse voltage test. I dont have a tester that will check gain etc

Ok I found something It looks as though someone has replaced R12 and R56 at some stage These are part of the input network around the attenuator relay. They are both supposed to be 68R according to the parts list but they have been replaced with 80R resistors. Furthermore the resistors...

Not sure if this is significant but neither jmp1 or jmp2 have any bridging clips on them I know jmp2 is the ptt sense either ground or +ve activated but not sure what jmp1 is for. Also both trim pots are straight up and down both in the centre of their travel

R37 next to TR16 looks like it has been getting hot at some stage but its still measuring appx 68r Cheers Stu

ps 5w input is only putting out about 100watts

Ok thanks for the info I'll do the tests you suggested across the bands Did a bit more testing after my last post and one pair of sd1446's is getting a bit warmer than the other pair The 2 nearest the case end stay relatively cool to the touch after a lengthy test transmission and the...

Hi All New member here. I've just acquired an RM HLA300 Solid state Amplifier but it needs a little sorting out. I'm hoping someone on here has worked on these. Its a revision 1.10 circuit board and has the 3 fans mounted on the heatsink. The main problem is the amp only seems to be...