peterson strobe tuner fix help needed

[martbot]

hi everybody. i'm trying to get a broken peterson strobe tuner model 400 working again and have hit a bit of a wall. here's whats going on and what i know.

everything seems to work except the motor. the power supply seems to be giving the right voltages. the strobe lights are on and respond to an input. the motor lookls like its trying to turn over but just moves about a quarter inch but does not spin.

naturally i began looking at the motor control board. the MJE711 was burnt out and the 3.3ohm resistors were testing high. tried replacing them but they just toasted again. everything else on that board seems to be just fine (although i'm not too sure about how to test the flipflops properly but all three share the same resistance readings). i can't really make any voltage reading on the motor board because it seems like it would start a small fire. with the motor board removed everything is stable and seems good.

what i'm considering now is either that the motor is dead. however bot coils are not open and have the same inductance so i'm not certain how to confirm that its dead.

the other thing i'm not sure about is the signal coming in from the tuning circuit. on the scope the signal looks like a spike up and then down. i don't really know what it should look like or if it could be frying transistors.

in any case, if anyone could point me in a good direction that would be great. i'd like to be able to confirm if the motor is alive or dead if anyone has any tips for that, or any other reccomendations.

thanks!

 

[ben7]

I think that motor is dead.
The windings will overheat sometimes, and they can short out, shorting the MJE711, causing the 3.3ohm resistor to burn too.

Do you know what voltage the motor runs on?

You need to check the motor coils resistance, not inductance!

 

[mbot]

the motor voltage is 24v. i checked the motor for resistance, both coils measure around 32-33 ohms. i checked the inductance before because i thought if that was off it might indicate something wrong. i have been assuming since the coils have the same resistance that the motor is probably still good but i just don't know how to confirm it.