Crate BT-100 Blows Fuse as soon as it's turned on

[Don Margeson]

I have a Crate BT-100 Bass Amp that blows the fuse as soon as it's turned on. It seems to be shorted to ground, and component on the board shows an ohm reding to ground.

[52 Bill]

Welcome to the place.

When an amp blows fuses at turn on, that usually means a shorted output transistor or a shorted power supply diode. It will take some work to figure out what your problem is.

What sorts of experience do you have in repairing electronics stuff and what sorts of test equipment to you have?

[Don Margeson]

Bill, I'm a Network Engineer

Welcome to the place.

When an amp blows fuses at turn on, that usually means a shorted output transistor or a shorted power supply diode. It will take some work to figure out what your problem is.

What sorts of experience do you have in repairing electronics stuff and what sorts of test equipment to you have?

I've repaired plenty of computers, monitors a,d switches/routers. I have a multimeter. I also have a desoldering station and soldering iron. The only power supply repair I have done is for bad caps. I do have the schematic save on my laptop.

[DrGonz78]

I think you should build a Light Bulb Limiter (aka Dim Bulb Tester). Whenever you have an amp that is blowing fuses the Light Bulb Limiter will help limit current if a short is present and will save your fuse. Also, once you fix the problem the first power up of the amp can be questionable still. With the limiter in place it can help prevent damage to the repaired amp if there might be anything shorted that you missed. So do a search for Light Bulb Limiter and build one. Stick to 60-100 watt incandescent light bulbs.

[Don Margeson]

I will try this tomorrow.

I think you should build a Light Bulb Limiter (aka Dim Bulb Tester). Whenever you have an amp that is blowing fuses the Light Bulb Limiter will help limit current if a short is present and will save your fuse. Also, once you fix the problem the first power up of the amp can be questionable still. With the limiter in place it can help prevent damage to the repaired amp if there might be anything shorted that you missed. So do a search for Light Bulb Limiter and build one. Stick to 60-100 watt incandescent light bulbs.

I'll post the results

Thanks!

[52 Bill]

It will be helpful if you post the schematic here, then we can all refer to the same part numbers, etc. when discussing what to check and test.

[Mick Bailey]

+1 on building a bulb limiter.

A couple of other points; Don't power the amp on with a speaker or other load connected. Also, to check if one or more of the output transistors are shorted, connect your bulb limiter and with your DMM probes connected to the speaker output briefly turn on the amp and measure if there's any DC on the output. If there's no DC you most likely have a PSU fault. The amp will 'hold' without blowing the fuse with a bulb limiter connected, but it's not a good idea to leave it running like this for more than a few seconds.

[Don Margeson]

Crate BT-100 Schematics and parts list

It will be helpful if you post the schematic here, then we can all refer to the same part numbers, etc. when discussing what to check and test.

crate_bt100_sch_and_parts.pdf