06-03-2013, 07:58 PM
I wasn't expecting to get back to it today due to a previous Lunchtime engagement, but that was reasonably quick and then my mate Pete turned up so I was able to escape.
So .....
First we had a poke about.
R508 looked as though it had been a bit warm, and sure enough it measured around 1M instead of the 680k it should have been. I changed it for one I had handy - as is usual my 2W kit doesn't include that value - but it made no difference.
All the other Resistors we measured were reasonable.
After some pondering I decided I'd remove the PCB and take it back to the house for a bit of Reverse Engineering. After some photographing and marking we removed the wires and fished out the PCB. At that stage Pete spotted another duff Hunts lurking across a couple of the Transformer tags. Fortunately enough had survived to read its value, 0.001/1n. Guess what I haven't got in stock? I had a momentary panic when I realised that the PCB is bolted to the chassis at 4 points via the track that runs round the LH edge, potentially making lots of my tests usless. However it turns out that there's alo a wire in the 'Back Connections' that is also a Chassis connection.
So, I'll order some bits and work out the circuit.
Alan
So .....
First we had a poke about.
R508 looked as though it had been a bit warm, and sure enough it measured around 1M instead of the 680k it should have been. I changed it for one I had handy - as is usual my 2W kit doesn't include that value - but it made no difference.
All the other Resistors we measured were reasonable.
After some pondering I decided I'd remove the PCB and take it back to the house for a bit of Reverse Engineering. After some photographing and marking we removed the wires and fished out the PCB. At that stage Pete spotted another duff Hunts lurking across a couple of the Transformer tags. Fortunately enough had survived to read its value, 0.001/1n. Guess what I haven't got in stock? I had a momentary panic when I realised that the PCB is bolted to the chassis at 4 points via the track that runs round the LH edge, potentially making lots of my tests usless. However it turns out that there's alo a wire in the 'Back Connections' that is also a Chassis connection.
So, I'll order some bits and work out the circuit.
Alan
