[SOLVED]Motor transistors keep dying on me

[map2112]

The snubber or bad diodes could explain the supply motor running all of the time, and also blowing up the supply motor transistor, but I am really wondering if there is enough leakage or a short between sections in that dual section run capacitor to power the supply motor from the take up motor. That could be the hidden interaction between the take up and supply motors running and perhaps also what blows up the supply transistor?

Without the transistor on the supply motor bridge there should be no correlation to any mode as there is nothing connecting it to the mode logic.

I think you are getting close to solving this mystery

 

[EmilFrid]

Yes, the weird thing is that supply motor works perfectly fine if it is the only motor having a connection to a transistor. But as soon as both transistors are hooked up, one of them blows up, and it happens randomly – sometimes supply, sometimes take up. I'm also wondering if there's any bad diodes or caps, and it will be interesting to see what happens after I change them.

I hope we're getting close to solving this mystery!

 

[RoadrunnerOZ]

I think the supply motor running is to provide braking via motor speed differential - as if it ran free there would be no tension (unless of course slip clutch braking is used) - probably regulated to run at slightly lower speed to control tape tension - the transistors and their control circuits for each motor would be set to provide this braking bias.

 

[RoadrunnerOZ]

Does the transistor blowing scenario happen with FF, REW or Play?

 

[EmilFrid]

Yes, but this "braking" effect should only be there if a transistor is there. That's what bugs me.

It happens in any mode, seemingly random.

 

[RoadrunnerOZ]

If the AC across D1/D3 junction and D2/D4 junction is only there when a transport mode is engaged then the 100V is turned on by the controller - without the transistor there is still the 47uF cap feeding the motor - this may be the whole point of that RC across the transistor to prevent spiking and back emf from the motor and incidentally providing some drive whether the transistor is there or not - I don’t think the transistor turns the motor on or off but regulates the voltage it actually gets

 

[RoadrunnerOZ]

If that’s a new controller maybe it’s faulty?

 

[EmilFrid]

The controller is not new, only the transport logic unit, but that one puts out all the correct voltages to the reel motor control circuit, and also all logic on the reel control board checks out ok as well. I feel like this issue might be emanating from a higher order level, from the power part of the circuit. I will start with run caps and diodes and then we'll see what happens from there. I was going to buy a new reel control card just to rule that one out, but my friend happened to have all boards except for that one.

 

[RoadrunnerOZ]

With the run caps there’s not just the dual cap, there are two more single ones - I assume youre doing all?

 

[EmilFrid]

I will start with the dual and move on to the rest of them if nothing changes. But I'm very curious of that dual one...

 

[RoadrunnerOZ]

There are two 5.3uF as well as the dual 2uF - I’d be doing them all

 

[EmilFrid]

Yes, I will definitely do this

 

[EmilFrid]

This will be the goal driving me to keep trying:

 

[RoadrunnerOZ]

Do you have a schematic for the Reel Motor Control Board 60800360?

 

[EmilFrid]

Will have a look when I get to the studio

 

[RoadrunnerOZ]

Ok

 

[EmilFrid]

Oh, I went back in the thread – that one is the schematic I've already posted (reel motor control)

 

[RoadrunnerOZ]

Which post # is that?

 

[EmilFrid]

 

[RoadrunnerOZ]

Yeah I’ve already looked at that diagram - are those two AC lines always active at pin R and pin 11 with respect to their own 0V at the motor or only active when in a mode of operation?