Farnell delivered some bits and bobs today. In amongst the parts were some replacement 500mW? 3.6V zeners for the faulty mid-band QMX and some 10V tantalum caps to replace the lower voltage parts in the Rev.1 low band QMX.?
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Having fitted the parts, my low band QMX is up and running. The mid-band QMX powered up with the new zener fitted and ran for a while but then popped it's clogs. There was a brief noise from the unit and then it stopped receiving and transmitting. The CPU is ok as the radio still powers on but it's completely deaf and there is zero output power when keying down.
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I opened the unit up again and could smell that something was getting hot. There were no obvious burned components and nothing was overheating in RX. On key-down (into a dummy load) the bs170's were getting toasty while there was still no RF output. A little isopropyl dabbed on the bs170's sizzled off quickly when the key was pressed.?
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To be honest, I'm getting a little fed up with this radio. I was dubious about it when I started building the kit as it was supplied without PSU boards and the man board itself looked a pretty grubby. PSU boards were delivered quickly when I raised a ticket but the 3.3v board failed resulting in my initial post above. I've built quite a few QRP labs kits and they've all worked first time and stayed working, apart from this one.... End Of Moan...
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I've removed the RWTS-wound output transformer and will rewind that and replace the four bs170's so I know those parts are all good. I I'm a bit concerned that the rig is completely deaf though. It does seem like there's something a bit more serious going on... Any suggestions for where to begin fault-finding on this one?
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Cheers,?
Ronan
MM0IVR?
