So I bought this unit in original box, from an estate sale with other gear. I hooked it up and got music through both channels, although when powered on I could hear a slight Humm, from the unit, not from either channel. So last night I pulled the cover to blow out any dust and see if it had any obvious issues. Well the left board (when facing the front of unit) had what looks like some resistors at the top and possibly a small Motorola w223440 (going from memory) transistor with burn marks. Not sure but a couple resistors look like they may have been replaced I could be wrong. I wasn't sure if there is still voltage in the circuit that could cause damage or shock, so I didn't touch anything. Should I pull that board and check the transistor and resistors with my vom? Do I need to discharge the big capacitors? Do I need to remove these components from the circuit or unsolder a leg, to get a proper reading? I can't tell if the black spots were from previous burnt resistors or these ones because I can read the values from the top. Sorry if these are dumb questions, but I don't want to damage anything or learn the hard way.
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yes, those are definitely new components. If they were the originals, they would look just as charred as the board below them. You could potentially measure the resistors in circuit to see if they’re close, as long as they’re not in parallel with other resistors or there isn’t a capacitor close in the circuit you should be able to get a fairly good reading. I’m guessing it was repaired and it’s just fine. The hum you are hearing comes from the transformer.
The char you were seen on the transistor is actually just the small plastic piece that sits underneath the transistor as a spacer. If it powered up and you got music, I would imagine that the last person in it fixed the faults and you’re fine.
Dan
The char you were seen on the transistor is actually just the small plastic piece that sits underneath the transistor as a spacer. If it powered up and you got music, I would imagine that the last person in it fixed the faults and you’re fine.
Dan
Thank you, sir!
That charring is due to a bad solder connection on the collector connection of that transistor socket.
You think? I had assumed that it was sitting a bit too close to the resistor just above it when the resistor flamed. The small plastic piece has been pivoted from its original position though.
Dan
I don't know if this view tells a different story. Also that Motorola Transistor has the red paint disturbed on the heatsink, so maybe it was replaced? It does have audio, so probably not going to worry about it for now. Also here's a pic of a service center label on the Hafler box, not that it proves anything. I bought it with other components, not sure if any of them worked, because previous owner passed, but so far everything works, and I got a good deal. Not sure if I will ever need this much amp, but I should give it a chance at least, and if I did find another owner, I can tell them about it's troubled past. Thanks, guys.
