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Ragtop
11-02-2017, 12:34 AM
Trying to find someone that repairs Control boars for 1987 FES Compressors using Micro II. compressor model is a FES 140 V that has a variable slide valve control.
we have several R-22 machines both high and low stage
Thanks for any help

NH3LVR
11-02-2017, 08:01 PM
Before I retired I used to get a lot of promotional material from a company that said they could repair anything. I only used them once, but it was for not for a compressor board. I can see if I can find them if you wish.

However I am replying for a different reason.
I have found that in many cases the issue with controls is not in the boards themselves but in the power supplied to them.
One of the issues is that the power supply will supply not only higher or lower voltages than designed, but also a AC component.
This can be measured by taking a reading as normal with the meter set on DC. Then switch the meter to AC. Divide the AC reading by the DC value. This will give you the AC component.
How much is too much? A friend of mine who works on such things tells me that no more than 1/10th of 1% is allowable. I feel that is a little low. I have seen troubles with circuits at 5%. Functions became erratic at that value.
I do not claim a great amount of expertise in this, Just relating my experience.
This became the first thing I checked when I had a issue.

Grizzly
12-02-2017, 09:35 AM
Hi NH3LVR.
Very helpful advise!

I had not heard about this AC component factor before.
Thanks Grizzly

Greek_engineer
12-02-2017, 06:26 PM
are you saying that in any circuit board we have to measure both DC supply and AC supply?
is that a good practice to find if the circuit board deviates from normal operation?
thanks!

NH3LVR
12-02-2017, 08:40 PM
Sorry if I was not clear.
On a system with a separate power supply you will have low voltage connections to the other boards.
What we are looking for is to verify that the boards are being supplied with the proper voltage and that the DC is as pure as possible. We want to see if what should be nearly pure DC is not contaminated with AC. The mains voltage is not what we want to look at.

I had a very erratically operating electrode chiller in a laser plant that could not be used. I had almost no service information on it. I started checking the low voltage supplied to the other boards. The 5 volt supply was low and had a large AC component.
In order to prove my theory I went to the test lab and borrowed a power supply. I disconnected the existing 5 volts DC and substituted for it. Problem solved.