Is there a general dead amp troubleshooting checklist/flowchart?

[Bear]

I picked up a Roland Jazz Chorus that is as DOA as was advertised.  My last buy-it-broken experiment had just needed deoxit, but this one is no lights/power/output, so I want a methodology to proceed on.

[Bear]

The Roland is a rust bucket, including the power transformer, chassis, and some of the on-PCB connectors.  Bugger has seen water.  So this might be a more specific rehab process, though I still could use a general approach.

[galaxiex]

If you haven't already, build a light bulb limiter. You will need it at some point.

See thread >>> http://www.ssguitar.com/index.php?topic=2093.0

From there, some obvious basic things to check,

Eyeball/check these things first.

Look for/smell burnt parts?
Fuse(s),
Internal mains wiring, switch,
Rectifiers, Main filter caps.

If you find a blown fuse and decide to stick a new fuse in and power it up... DON'T! ...unless you have the amp plugged into the light bulb limiter.

I'm just a noob at this, so more experienced members will probably have more to add,
but the above is where I would start with a dead amp, eyeball/smell/check the mains wiring and transformer etc, to see if I have basic power in.
And I always use a light bulb limiter until I am sure the amp can withstand full mains power.

Do you have a multi meter and know how to use it? Not being condescending, I don't know your experience level.

[Enzo]

Troubleshooting is a specific skill, it applies to any circuit.  The essence is this:  isolate the problem.

If there is no sign of life, then check the obvious.  Is the fuse blown?  Is the power cord cut?  Pull the plug and hold it in your hand, turn the amp power switch to ON, then measure resistance between the main prongs of the power cord.  You are measuring the resistance up one side of the cord, through the fuse and switch, through the transformer primary and back down the other side of the cord.  If all that is intact, you will get some smallish resistance, say 50-200 ohms.  If you get an open or infinite resistance then the circuit is open.

Open primary circuit, use your meter to check the fuse in its holder, the switch, and the transformer primary right at its wires.  And with power applied, we check that 120vAC is appearing right at the primary wires.

Primary OK, then power up and see if the secondary transformer windings are producing voltages.

If the fuse blows and the bulb limiter tells you another fuse WOULD blow, then we look for shorted parts.  First power transistors, next rectifiers in the power supply.  That will be 90% of them at least.

If we can separate parts, do so. If we can disconnect the power amps from the power supply, do it and see if the power supply alone blows fuses.  ("blows fuses" is code for bulb gets bright)

[J M Fahey]

Is there a general dead amp troubleshooting checklist/flowchart?

yes there is, and it started being suggested above ....

BUT

The Roland is a rust bucket, including the power transformer, chassis, and some of the on-PCB connectors.  Bugger has seen water.

means it won´t apply, not straight away at least, because this is no "an amp which was working and developed an "electronic" problem" but "a bucket of rust".

Hope you didn´t pay more than $50 for it because that´s what it´s worth as is.

Please post a few pictures showing chassis inside, transformer, heatsink, cabinet, speakers, until then no regular testing procedure can be suggested or applied, the power transformer may very well explode or short mains voltage to chassis or exhibit any other VERY nasty behaviour.

Sorry

[Bear]

$40, so I got a deal. :loco

I figured it was worth a chance for that price.  If the PT isn't shot.  I'll get some pictures up next weekend if I'm not swamped.