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DC-300A Series II - Power down sound


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#1 g.bieber

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Posted 10 April 2005 - 04:55 PM

I just bought and older 15+ year DC-300A Series II

It works great, but has an odd puttering sound when I power it down. I noticed the IOC indicators are lite when this sound is produced. Has anyone else experienced this?

Can anyone offer a repair tip or procedure? I was thinking I would start by checking the memory capacitors in the IOC circuit, would this be a good starting point?

Thanks,

George

#2 DGlass

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Posted 13 April 2005 - 02:59 PM

the IOCs will come on during shut down as the power supplies drain so I don't think the issue is in the IOC circuit. More than likely it is an imbalance in the power supplies draining. One of our service techs has suggested making sure the screws are tight on the *beep* terminals for the large 13,500 uf caps.
Just make sure they are suggged don't over tighten them or you may break the terminal. Sometimes if these are loose it can cause them to drain at a different rate.

#3 g.bieber

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Posted 18 April 2005 - 06:48 AM

QUOTE(DGlass @ Apr 13 2005, 02:59 PM)
the IOCs will come on during shut down as the power supplies drain so I don't think the issue is in the IOC circuit. More than likely it is an imbalance in the power supplies draining. One of our service techs has suggested making sure the screws are tight on the *beep* terminals for the large 13,500 uf caps.
Just make sure they are suggged don't over tighten them or you may break the terminal. Sometimes if these are loose it can cause them to drain at a different rate.
View Post


I tried snugging up the screws and cleaning the ring terminal contact surfaces on the capacitors, but I am still geting a difference of over 10 volts between the + and - supplies at the capacitor terminals during power down as they discharge. The puttering sound did appear get a little better, but did not go away completely.

Could the drainage rate difference be due to the 13,500 ufd capacitors getting  leaky due to age? If so what is the safest method of testing them outside of the circuit to verify they need to be replaced.

Any other suggestions to determine the cause for difference in drain rates between the supplies?

Thanks for the help,

George

#4 DGlass

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Posted 18 April 2005 - 08:34 AM

QUOTE(g.bieber @ Apr 18 2005, 06:48 AM)
QUOTE(DGlass @ Apr 13 2005, 02:59 PM)
the IOCs will come on during shut down as the power supplies drain so I don't think the issue is in the IOC circuit. More than likely it is an imbalance in the power supplies draining. One of our service techs has suggested making sure the screws are tight on the *beep* terminals for the large 13,500 uf caps.
Just make sure they are suggged don't over tighten them or you may break the terminal. Sometimes if these are loose it can cause them to drain at a different rate.
View Post


I tried snugging up the screws and cleaning the ring terminal contact surfaces on the capacitors, but I am still geting a difference of over 10 volts between the + and - supplies at the capacitor terminals during power down as they discharge. The puttering sound did appear get a little better, but did not go away completely.

Could the drainage rate difference be due to the 13,500 ufd capacitors getting  leaky due to age? If so what is the safest method of testing them outside of the circuit to verify they need to be replaced.

Any other suggestions to determine the cause for difference in drain rates between the supplies?

Thanks for the help,

George
View Post


The next thing to do is check the capacitors. There are three things you can do. The first one is to look at both the positive and negative supplies as they drain with an oscilloscope. Second swap the capacitors and see if they drain more uniformly. Third pull the capacitors and check them with a capacitance meter.
(Note: make sure the capacitors are discharged before doing number three)

#5 trollwatcher

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Posted 19 September 2006 - 06:53 PM

I don't know if this relates to your issue, but I have had lots of 300As and 300A series 11s over the years, and they will make that sound with IOCs fully lit up when you switch off the power, gain controls are still up and audio coming in from a pre amp etc.
i.e. that's normal!

If this is not the case, then yes it's time to get out the thinking cap and fixing gear... sad.gif

Good Luck smile.gif