crown mt2400

[e_c_mccollum]

Got a little problem. After powering up mt2400, channel 1 sounds distorted. Noticed R02 (5.6ohm) has no voltage across it. R21(5.6ohm) has spec voltage across it. High side is obviously not on. R02/R21 resistors test good.

Low side and high side trans tect good. VCC -/+ at idle is 61 volts dc on collectors of outputs.

[Mark Black]

I've had bias trimpots get very dirty/intermittent/open on Crown Micro & Macro amps. I don't think I ever noticed if there was a lack of voltage across the 5.6 ohm (just wiggled the pot adjust while looking at the output) but it might be something to look for.

Other things might be bad diodes in the bias string or a flaky connection at a driver transistor (especially if the amp is of the vintage to have the drivers soldered to right-angle header pins). Also might want to check the heatsink-embedded bias transistor.

[e_c_mccollum]

Swaped out the embedded bias transistor to the other channel to see if problem would follow to channel 2. Both channels now work. I think that channel bias trans had bad internal lead connection. Will be replacing both channels for a piece of mind.

[e_c_mccollum]

Found ODEP to be messed up to. Need replacement for the dual transistors 2sc3381 and 2sa1349.