The Craftmans Shop > New from Old
The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
awemawson:
And a bit more progress. The OMM PCB and probe have arrived with PK in Perth, Australia and he has it on the bench with power on and is looking at it. I just hope it doesn't make his head spin like it did mine !
Thanks PK :thumbup:
PK:
So the first thing you do when someone says: "Can you take a look at this for me, it's doing X,Y, and Z", is fire it up and check that its actually behaving that way and there are no other obvious faults.
Next we took a look at the negative voltage reg. It is used to generate -5V for the amplifiers and comparitors under that shield.
It looks like the 6.8uF cap on the screen is the output capacitor for this reg. It isn't, it's a 68uF cap a bit further away. This was removed and replaced but the voltage was still low.
The reg chip was removed and replaced, and the voltage dropped a bit lower to 2.7V! I guess they don't make 'em like they used to.
I lifted the output pin and connected a small cap to ground and the voltage shot up to 4.9V So it's probably something overloading the reg.
Out came the thermal camera (and yes, I forgot to snap a pic) and one chip in particular was running quite a lot hotter than the others. An LM833 audio amp. Now this may still be a red herring, as audio amps sometimes run hot, and often drive low impedance loads... In any case, it was asked to leave the premises and we now have a -4.7V rail.
I think we'll just order every chip on the board. There's no unobtanium in this thing...
Oh, and if all this talk of ripping components off expensive PCB's generates anxiety. Don't worry, it's not my PCB.. :thumbup:
Pete.:
--- Quote from: PK on September 28, 2018, 06:50:51 AM ---Oh, and if all this talk of ripping components off expensive PCB's generates anxiety. Don't worry, it's not my PCB.. :thumbup:
--- End quote ---
I could really like this guy :) :) :)
mc:
--- Quote from: PK on September 28, 2018, 06:50:51 AM ---Oh, and if all this talk of ripping components off expensive PCB's generates anxiety. Don't worry, it's not my PCB.. :thumbup:
--- End quote ---
Now that's the kind of attitude I like! :D
awemawson:
Yikes PK :bugeye:
. . . but progress - good stuff. Look at the smd transistor that has an arrow scratched pointing at it on the semi-circular trace that the can sits on - that's the one that looked to be s/c collector base, but it could be the op amp it's connected to which is an LM833
That's an impressive magnifying set up that you have there :thumbup:
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