AC Drive

You do not mention what brand or model drive you are using?

Getting circuit diagrams for ac drives is difficult (if not impossible) as the designs are proprietary and manufacturers have a tendency not to make them available, even to there suppliers and service agents. From my experience they prefer you to send them back to them for board-level repair.

Your best bet would be to go back to your supplier and look at warranty repair/replacement or potentially return the drives so they can be sent back to the manufacturer for inspection and report. I have had to do this on occasion and it did work well to help track down the cause of the problem, rather than trying to delve into a multi-layer PCB covered in surface mount devices with no documentation to assist!

Jack - former ac drive supplier and service agent.

thank you sir,

we are using baldor made drives

and also its multilayer PCB i will return it to supplier,but actually i want to know that this type of breakdowns are usually do by technicians or not? and why hyperabrubt variactor diodes are used there in voltage devider circuit end?

i want to know that this type of breakdowns are usually do by technicians or not?

It depends, basic testing only requires some understanding of the drive, the manual, a mechanical or electrical motor load, some spare parts (like control boards and removable memory modules that could be swapped out) and some time. A technician could do the job with the right tools and information.

Board level inspection and repair is much, much harder however and due to its cost is not really worth it except for the drive manufacturer, and even then they may just replace the faulty control board or entire drive due to it being cheaper than performing a detailed diagnosis and (attempted) repair.

a good place to start is a close inspection

look for black spots where parts or solder traces used to be, bulging capacitors...

as Jack says if you have a few identical drives, swap assemblies into know good units, including having a test load

if it gets much beyond easy stuff, to multipin IC's or surface mounted components

it's probably not worth the trouble

If it is just a 'voltage devider and end of that there is variactor diode', you should be able to reverse engineer the board and find the relevant components between pin 7 of the 3844 back to the DC bus.

The 'variactor diode' in this case is probably a 30v zener. Either

a) a resistor in the chain has gone open

b) the diode has gone short and/or

c) the chip is faulty.

Good luck.

I saw mention of 550vdc drives and 24vdc generation. Are you sure there is not supposed to be a separate control voltage input.

1. That is a very steep drop for a divider to go from 550 to 24.
2. Are you sure that the diode is a variactor diode? Typically the diode on a circuit like that is a zener diode. It will have a very sharp Vr arround 24vdc and the resistor must dissipate all energy between the raw supply and pin on the FET gate or transistor base. My guess is one of the components can't handle the power dissipation going from the top of the resistor to the load or the collector / drain of 3 terminal device to the load. If you run the system at high frequency the transistor / FET must dissipate more energy to control all the power switches.
3. Recheck the wiring diagram for a separate control power voltage input if you like.
4. The recommendation to talk with the supplier is probably the best bet. They want you to be successful with there products.

hii regsoft,

thats 550vdc is the bus voltage,actual 24vdc controll voltage is created by pwm process

that mean 3844b ic generates o/p pulses which is fed to mosfet whose o/p is exact 24vdc.

but here my prob is,to gets ON 3844b ic pin no 7 should have 30vdc.this voltage getting from 550v bus line,and this is through voltage devider circuit,and also there is some capacitors r there.this 30v is not present there.because this is multilayer PCB i cant able to trace the circuit.

but any way i contacted to manufacturer,for repair the drive