Could you list any (probably) keyboard internal problems that would cause the fuse in the adaptor to blow, in a PC88MX (yes it's 20 years old *L*). The original fuse blew a couple of weeks ago, after

Pull the connector from the back of the PTO switch and the 4 wire connector at engine. Replace fuse. Turn key to run.

Did fuse blow? No, turn key to start and back to run.

Did fuse blow? No, plug in engine connector.

Did fuse blow? Yes, likely shorted regulator or safety miswired.

Plug in PTO switch.

Did fuse blow? Yes, likely safety miswired.

Does the fuse holder or wiring diagram have the fuse size listed on it ? It could be an incorrect fuse size from the factory or installed by someone who was just lucky the day they installed it and it ran with what is essentially a fuse with too low a rating.
Are you using the correct voltage rating ie 120volts not 12volts or whatever.
IF IF the second fuse works that kinda tells me there is no fatal short in the system, otherwise it would blow that fuse also.
I would try a 20amp or a 17.5amp if it's made in the configuration you need. Preferably the 17.5.
If you replace the 15A with the 20A and it blows then you have a problem.

It's very hard to exactly diagnose your problem exactly without being there. I'd say you have a power supply issue inside the keyboard. Maybe a shorted filter or diodes. If you have replaced the AC adapter, be sure that the polarity, voltage and current rating is correct.

The short answer is yes, it can be repaired. The internal fuses are usually speaker protection fuses. If they blow right away, the likely problem is shorted outputs. The original exact replacement may no longer be available, but any shop that repairs audio gear will be able to find replacement parts.

Update this if you need more info.

Dan

There's an internal fuse - about 20 Amps. It usually blows when the magnetron dies. Unplug the unit from the wall and access the internals. You should plainly see the fuse holder - remove and check the fuse. Spares are available at any ACE hardware store. If the unit is more than 5 years old, I wouldn't mess with it.

That "switch" is really a 10 amp ciruit breaker, which is a resettable fuse. Like any fuse, if resetting/replacing it just causes it to blow again there is fault in the internal circuitry that is drawing too much current.

You problem is likely to be one of the following things:

1. The motor has failed with an internal short.
2. The motor or something in the belt drive has siezed.
2. The motor controller board has failed
3. A connection wire has shorted, possibly by the insulation being worn away rubbing against a metal part.

Most devices that can be operated from external supplies have a diode across the the power jack that will short the source if the polarity is reversed.
Since this is a pretty small part without much chance of surviving the current available from a cigarette lighter socket, the only hope you have is that the fuse almost always found in these 'adaptors' will blow before the diode fails.

If the radios will not operate from batteries, I'm afraid they are badly damaged.

It son't hurt much now if you open the case and check near the power jack for burned parts. The diode(s) probably aren't there at all any more since they are commonly capable of no more than an amp or two and the typical fuse in those car adaptors is 5-10 amps, enough current to cause the diode to explode before the fuse blows.

I don't know where you reside, but in the US there are many sources for low-cost digital multimeters (<$20 US) that would have prevented your problem simply by checking the polarity of the jack before plugging it in.
I don't think the lighter was at fault; I believe the adaptor was wired for a particular item, just not for your radios.
It's always chancy to use a power source only because the plugs match.

Most devices have a small symbol molded into the plastic near the power jack showing which polarity input is correct.

check your thermal fuse its about 2 inches long white on the outside black on the inside it has 2 wires going to it check for

cotinuity becareful of the capacitor you need to disapate that first by touching the two teminals together with a screw driver

If it blows the fuse as soon as you hit the START button, it's almost certainly a shorted high-voltage capacitor.

If it blows a few seconds after you hit the START button, it's probably the high-voltage transformer. You'll possibly also smell a faint electrical burning smell from the rear vent after you shut if off.

If it blows the fuse as soon as it's plugged in, you probably have a shorted door switch, a shorted varistor, or an internally exposed wire shorting to the chassis, etc.

I am a recently retired appliance engineer of 20 years, microwaves are not normally things worked on yourself, i would be reluctant to help normally but yes there is an internal fuse ( a special quick blow type )just inside where the wire enters the cabinet on a small circuit board, if a replacement is needed it must be exact match bought from an electronic shop, microwaves are dangerous they store powerful electric and can still shock after removing the plug, if the replacement fuse blows, there is a fault elsewhere, and i do not recommend further self repair, work with safety