Anyone With VFD Repair Experience?

I lost an Omron 3G3JV inverter to a power surge last week. I popped the cover off today and saw that capacitor C5 blew. A cursory visual inspection (I haven't unsoldered the 10 leads to totally free the board) and a sniff test don't show any other apparent damage. What are the odds of replacing the 220uf 400V electrolytic cap and having it be in working condition?
I've done some bench repair 20+ years ago and am not current with the surface mount soldering techniques. I just hate to trash it if there's a cheap fix.


-Mike

Hi Mike,

If it were mine, I'd replace all the HV electrolytics and the rectifiers that feed them.

Power components which have been stressed can fail in the future even if they work OK now.

You should be able to get the needed parts from Mouser (no minimum order) www.mouser.com

- Leigh

Replace the cap, check the bridge rectifier feeding it and replace any MOV's It would be likely that one of the diodes in the bridge rectifier failed short circuit and subjected the cap to AC. If you were local I would give you the cap and a rectifier from a dead drive, they are piling up around here mostly with controller faults, the power side seems to be more reliable.

On some older drives it is possible to power up the control side without the DC BUS voltage being present thus providing a means to check the controller before spending any money on the drive. Alternatively the DC bus voltage can be provided from another drive, the controller will then give a phase failure or similar fault indication in which case it will be worth spending money to replace the defective components.

Many drives have most of the components, except for the caps, within the IPM (integrated power module).

The rectifier will be a "six-phase" configuration (three-phase full-wave), employing six diodes in a three-phase drive, and will be a "two-phase" configuration (single-phase full-wave), employing four diodes in a single-phase drive.

Voltage-doubler drives are known, and these have twice as many caps, but also a direct connection between one line, usually N, and the center of the cap bank, with equal number of caps in parallel on either side of this connection.

It is possible to make a 120/240 drive, but I've not seen such a drive in practice. Conceptually, this connection would be present in a 120-to-240 drive, but absent in a 240-to-240 drive.

Manufacturers usually leave very few options available to the end-user, save programming provisions.

A negative TEMPCO resistance follows the diodes, and this comprises the "soft start" circuit.

The capacitors across the DC bus are after this "soft start" circuit.

In 230 volt drives, capacitors are usually rated 450 volts (325 volt dc bus) and 105ºF. In 460 volt drives, two caps are placed in series to obtain a 900 volt rated cap (650 volt dc bus).

The boards may be laid out to accommodate multiple paralleled caps.

One design I am familiar with has places for six caps, but on a standard unit only four are "stuffed", leaving two positions empty.

In this same design, all components, except for the caps, are within the IPM, and it is, therefore, impossible to effect a "component level repair", save for the caps.

The one "raw" board is applicable to several models, with each variation having a different number and capacity of caps, and/or a different IPM.

One "raw" board per frame size is theoretically possible.

If one cap has failed, all should be replaced as the exact failure mode might not be immediately apparent.