Mc60 speed controller help

Thread Starter

Dismantler1

Joined Nov 10, 2017
4
I have a couple mc60’s that I use to power various things. 1 of them is used on a small lathe. I was cutting some H 13 steel, which is really hard. The controller is Powering a 3 hp motor. Admitting Lee, I was probably pushing the motor and board as far as they could go. The circuit breaker blew. The breaker wouldn’t reset unless I unplugged the board. After taking the boat out I did a few checks with the multimeter and there was continuity between both of the AC input leads. I found the diagram that everybody uses for diagnosing the circuit, and figured I would start with R4 which is a 1N4005 diode. I removed r4 And are four was causing the problem, because now there wasn’t continuity between the two 120 V input and R4 was acting like a solid piece of wire, and not a diode. I replaced R4 and as soon as I plugged it in it blew the breaker and the new 1N4005 diode again. So there’s obviously something further back in the circuit that isn’t working correctly that is blowing R4. Any help is appreciated.
 

philba

Joined Aug 17, 2017
960
You could start by providing the diagram.

By the way, your spell check is kind of humorous but I will Admitting Lee say I never use it...
 

MaxHeadRoom

Joined Jul 18, 2013
22,855
Are you talking about R4? or D4? which is a diode rectifier it is a for the 12v supply.
Over loading the drive should not blow that.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
22,855
For testing, disconnect motor, use a 100 lamp if necessary.
Check bridge components, diodes and SCR's for short circuit.
Make sure D6 is not on (LED).
Max.
 

philba

Joined Aug 17, 2017
960
I'm having trouble with that schematic - it seems to be showing R16 as a 1K ohm resistor in series with the motor. That would limit the current 120 mA. Clear that isn't right. It looks like there is some faint text under the darker text on that schematic but I can't read it. I'm guessing that the darker text was added later. Perhaps R16 is also a .01 ohm resistor like R28.
 

Thread Starter

Dismantler1

Joined Nov 10, 2017
4
For testing, disconnect motor, use a 100 lamp if necessary.
Check bridge components, diodes and SCR's for short circuit.
Make sure D6 is not on (LED).
Max.
I have everything disconnected, the motor and the potentiometer that speeds up and slows down the motor. I’m only trying to connect the mains to the board and it’s short circuited. I disconnected D4 again and the mains aren’t short circuited again and the new D4 I put in is also shorted, continuity in both directions. Merely plugging in mains only blows D4. I’ve visually inspected the whole board and it looks pristine. Do I need to remove all the rectifier diodes like the D4020’s and the S4020’s to test them? Or can they be tested on the board?
 

MaxHeadRoom

Joined Jul 18, 2013
22,855
I'm having trouble with that schematic - it seems to be showing R16 as a 1K ohm resistor in series with the motor. That would limit the current 120 mA. Clear that isn't right. It looks like there is some faint text under the darker text on that schematic but I can't read it. I'm guessing that the darker text was added later. Perhaps R16 is also a .01 ohm resistor like R28.
There are some schematics that have been reverse-eingineered and have mistakes, if you look at the A+ line this should be fed direct from +ve terminal of the output of the SCR bridge.
R16 actually goes back to the trigger of the top SCR.
R28 is the only resistor in series with the motor .01Ω
@Dismantler1 You may need to remove D1,D2,Q2,Q3 but first check the resistance across the anode/cathode.
Max.
 
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