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Dec 4000 VLC

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Hjalmar

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Joined
Apr 28, 2022
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6
I have a Dec 4000 VLC that the power supply will run fine for awhile and then start cycling on and off. It has been recapped as every one I have seen has caps on the low voltage side leaking. The 5 volt line is high at 5.24 volts.

Is there a schematic around somewhere for the board? I have tried it in two different machines with the same result so I don't believe it has anything to do with the rest of the system.

If anyone has any experience with these I could sure use some ideas as to where to go. I have another supply but it only worked for a few minutes and is now dead.

Thanks
Todd
 
Hjalmar said:
I have a Dec 4000 VLC that the power supply will run fine for awhile and then start cycling on and off. It has been recapped as every one I have seen has caps on the low voltage side leaking. The 5 volt line is high at 5.24 volts.

Is there a schematic around somewhere for the board? I have tried it in two different machines with the same result so I don't believe it has anything to do with the rest of the system.

If anyone has any experience with these I could sure use some ideas as to where to go. I have another supply but it only worked for a few minutes and is now dead.

Thanks
Todd
Click to expand...
No experience with this specifically, but with problems of this type. If you can operate it with the cover off, try blowing on parts of it with a hot air gun (not set too high) and see if you can cause the problem to occur by heat - then note what you were pointing at at the time.
 
Okay I will see if that shows anything. The thing that worries me is the spec for the five volt rail is 5.1 and what it's running at is right at the edge for too high of a voltage listed in the manual.

Thanks
 
I have a couple of VAX 4000 VLC boxes. Both started misbehaving a bit recently (run for a while then reboot). Noticed the boxes were getting really warm.
Opened them up, and found the fans on the power supplies had stopped rotating. Boxes ran fine opened with external fan blowing into the power supply slots.
So pulled the supplies and replaced the fans. So far so good they are running fine again. So check your power supply fans to start.
 
Fans are running, I've tried with the cover on and off the machine and the same results. Be sure to check the Nichon caps on your machine. Most I've seen lately from the 90's are leaking. Not feeling the best today so I'm going to hit it again tomorrow.
 
Hjalmar said:
Fans are running, I've tried with the cover on and off the machine and the same results. Be sure to check the Nichon caps on your machine. Most I've seen lately from the 90's are leaking. Not feeling the best today so I'm going to hit it again tomorrow.
Click to expand...
thanks for the heads up. Having just had issues with a vaxstation 3100 it must be time to re-cap the vlc ..... is my favourite machine
 
Keep us informed when you re-cap the VLC, I have one of these also, and would like to know how to proceed.
 
Does anyone know what the pins and jumper are for on the low voltage side of the power supply? Every board I've seen so far has it jumpers to the pin closest to the LED.
 
The pins close to the cluster of diodes? Those are for the fan speed regulation. A single diode in the chain burns approx. 0.7 Volts.
 
Thanks, I was looking for a way to drop the five volt line down to 5.1 as per the specs.
 
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