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-   -   Motor control board repair (https://www.badcaps.net/forum/showthread.php?t=100397)

R_J 11-12-2021 02:42 PM
Re: Motor control board repair
 
Quote:
Originally Posted by cyclones (Post 1083716)
It looks like the -15V goes back to SR3 and the voltage regulator that doesn't get warm, AVR2. From looking at the trace lines and from the meter, it seems like the AVR2 is in parallel. SR3 has a + and - and two middle pins that go to the AC input, so it seems like a rectifier bridge, but I don't know what the SR3 designation could mean. Any ideas?
Are you getting a/c voltage to SR3? It is likely a bridge rectifier, why it is labeled SR3, who knows.
If you are not getting any a/c to the bridge, check the resistance of the traces and the power supply winding that supplies that circuit.
What is the part number on SR3?

cyclones 11-12-2021 07:45 PM
Re: Motor control board repair
 
Quote:
Originally Posted by R_J (Post 1083828)
Are you getting a/c voltage to SR3? It is likely a bridge rectifier, why it is labeled SR3, who knows.
If you are not getting any a/c to the bridge, check the resistance of the traces and the power supply winding that supplies that circuit.
What is the part number on SR3?
Is it going to be safe to power up the board with 120VAC? That's about 10% higher than the 107V at the machine. I assume any voltage regulators should be able to handle that but just wanted to check first since I've not dealt with something that is expecting 107V.

sam_sam_sam 11-12-2021 10:40 PM
Re: Motor control board repair
 
If this machine has a step down transformer that supply’s power to this board look and see if it says 110 volt or not because if does do you know if your facility has a hot leg if it does then you might have the transformer on the wrong set of legs because if the step down transformer says 110 to 120 volts output

Because I has this happen to me one time and when I switch the legs to a certain way I got the correct voltage however do not change the machine main power supply legs unless you do NOT have any other motors on this machine because your rotation might be wrong

R_J 11-13-2021 08:35 PM
Re: Motor control board repair
 
Quote:
Originally Posted by cyclones (Post 1083857)
Is it going to be safe to power up the board with 120VAC? That's about 10% higher than the 107V at the machine. I assume any voltage regulators should be able to handle that but just wanted to check first since I've not dealt with something that is expecting 107V.
It should be ok, but you could also just check the resistance like I said. The transformer winding should connect directly to the ~~ connections on the bridge rectifier.

cyclones 11-17-2021 10:24 AM
Re: Motor control board repair
 
Quote:
Originally Posted by R_J (Post 1084049)
It should be ok, but you could also just check the resistance like I said. The transformer winding should connect directly to the ~~ connections on the bridge rectifier.
Yes, it does. I measured half an ohm (0.5 ohms) resistance on the traces. The letters and numbers on the apparent BR are LBA 63.

R_J 11-17-2021 11:26 AM
Re: Motor control board repair
 
I suspect you have the -15 volts, It was only missing because the main transformer was not being used.

cyclones 11-17-2021 05:47 PM
Re: Motor control board repair
 
Quote:
Originally Posted by R_J (Post 1084977)
I suspect you have the -15 volts, It was only missing because the main transformer was not being used.
I tried it in the machine with everything connected and the -15V was missing.

cyclones 11-17-2021 06:30 PM
Re: Motor control board repair
 
Quote:
Originally Posted by cyclones (Post 1085028)
I tried it in the machine with everything connected and the -15V was missing.
I just connected my DC power supply to the middle pins of SR3 (where the AC is supposed to go) and supplied 20 volts and the -15V rail comes up.

R_J 11-17-2021 06:33 PM
Re: Motor control board repair
 
That proves the bridge rectifier and the rest of the -15v circuit is ok. The fault is then with either the transformer not supplying the a/c to the bridge or there is a break (or small fuse) between the transformer and the bridge rectifier.

I hope the transformer was NOT connected when you applied the 20 volts to the bridge? if it was that may have opened the winding on the transformer as the winding would be a very low resistance to the 20vdc.

cyclones 11-17-2021 07:22 PM
Re: Motor control board repair
 
Well, I found the problem causing no -15V. It's the connector. It's not making good contact, but I'm sure I accidentally bent that pin when I was originally trying to measure transformer output voltages. So I'll have to either fix that or replace the connector. I've seen this type before so I assume I can find one.

So now I guess I power it up on 120V with attention to that connector and see what I get.

sam_sam_sam 11-20-2021 10:53 AM
Re: Motor control board repair
 
Let us know if you were able to fix this board issue or not


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