DISTRIBUTION MAINTENANCE BULLETIN B22MB96002
01234567-6-X2X456X8XXX
February 23, 1996


SUBJECT: SNUBBER BOARDS FAILURES ON 30015CR*, 30015M4*, 30015M5*, 30015M6*, 30022F8* MACHINES (P/N 08BNCMBB)

Dear MILNOR Dealer/Customer:

We have seen a number of failures of resistors on snubbers boards, many of which may go unnoticed or misdiagnosed. Your understanding of snubbers and their functions is critical to proper diagnosis and repair.

SNUBBER FUNCTIONS: These devices are used to diminish electro-magnetic interference (EMI) caused be relays, motors and switches in use on the machine. A snubber is comprised of a resistor and capacitor which is placed in parallel to the electrical load (example: contactor, relay and valve, etc.) yet has no effect on the operation of the load. If the resistor or capacitor fail "open", then no effect on operation may be noticed. However, if the EMI created by the load is high enough, the machine microprocessor may "reset" or "crash" causing an interruption in machine service.

We have used a variety of snubbers in many machines that are produced at MILNOR. Some snubbers are in a "single package" and have wire leads tied directly to the load. Others are mounted on bards, as would be found on the machines listed above. These board mounted capacitors and resistors (snubbers) are much easier to connect in the circuit when mounted on a board. This is why we use this type of snubber arrangement on these machines.

THE PROBLEM: The snubber board was originally produced with a 1/4 watt resistor. After many years of use and equipment, we noticed a relatively low failure rate of these resistors an changed to a 1/2 watt metal film resistor which retained the 1/4 resistor package size. Much to our surprise, the 1/2 watt metal film resistor failed in mass quantities.

We then made a change to 1/2 watt carbon resistors and have since has no snubber failures.

Please see figure 1.

The resistor on the left is a 1/2 watt carbon resistor. Notice that its size is greater than that of the 1/4 watt resistor in the picture (Figure 1 right).

We are asking that your field service engineers carry a supply of snubber boards with them at all times. If a machine is found with a snubber board which contains a 1/4 watt resistor package (like on the right in Figure 1), we would like him to replace this board with the ne 1/2 watt snubber board.

Any snubber board returned with 1/4 watt resistor packages will be honored under warranty.

Additionally, please check your spare parts inventory for any 1/4 watt resistor packages mounted on snubber boards. These should be returned to MILNOR for credit or replacement.

TECHNICAL NOTE: A failed 1/4 watt resistor package is difficult to detect. However, there is a small "burn" on the resistor which indicates a failure . Remember that "nuisance" resetting or crashing of the microprocessor is the symptom of failed snubbers.

If any questions arise, please call MILNOR Technical Support at 504-467-9591 ext. 276.

Sincerely,

PELLERIN MILNOR CORPORATION

Gary L. Lazarre
Manager
Customer Service

GLL/das