Collins Power Rock Audio Hum??

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radioman1992
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Collins Power Rock Audio Hum??

Post by radioman1992 » Wed Oct 12, 2016 7:34 am

I recently started helping an Am Station Which Has A Collins 5Kw Power Rock, The Station has a noticeable hum when operation on this transmitter, I have checked the audio right up to the input of transmitter and found it to be clean and no hum. I am new to this model of transmitter and figure the brain trust here could help.. two thoughts that have crossed my mind is the low voltage power supply might need re-capped or there is an issue in the PWM Card.. Any thoughts???

COMMENG
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Re: Collins Power Rock Audio Hum??

Post by COMMENG » Wed Oct 12, 2016 10:35 am

...the low voltage power supply might need re-capped or there is an issue in the PWM Card.
It could be those as well. There is power supply feedback via a ladder circuit to the PDM circuit to reduce hum.

It may be the electrolytics in the LV PS and in the PDM card need replacement. Have any upgrades been done in this area? Any logging info or documentation that caps have been replaced?

I would also check the condition of the 2.1 uf filter cap in the HV supply and the associated wiring.

Also check to make sure you have all three AC phases to the power transformer.

Be extremely careful as this puppy has a 13.5kV power supply. Never assume that cap has been properly bled by the bleeder resistor.



You might also contact this group:

http://mwpersons.com/tech-tips/AM/315R- ... mitter.htm


COMMENG

W2XJ
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Re: Collins Power Rock Audio Hum??

Post by W2XJ » Wed Oct 12, 2016 6:59 pm

Check for RF feedback first. Disconnect the program line, put a 600 ohm resistor across the input and see if there is still hum.

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Dale H. Cook
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Re: Collins Power Rock Audio Hum??

Post by Dale H. Cook » Thu Oct 13, 2016 5:45 am

COMMENG wrote:Be extremely careful as this puppy has a 13.5kV power supply. Never assume that cap has been properly bled by the bleeder resistor.
I will second that - it is why you have fore-and-aft Jesus sticks - use them diligently.

Have you looked at the PWM waveform with no modulation using a 'scope to see that it has the correct duty cycle?

BTW, the Power Rock came in only a 5kW model (Collins 828E-1, later Continental 315R-1). After the line was sold by Collins to Continental the latter introduced a 1 kW variant, the 314R-1, aka the Power Pebble.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

RodeoJack
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Re: Collins Power Rock Audio Hum??

Post by RodeoJack » Thu Oct 13, 2016 1:31 pm

I have two in service myself. One is a daytime primary & runs great. The other is a standby I just brought back from a 13-year slumber. It works well enough, but has a couple of issues I need to work out... one of which may be the same hum Radioman is dealing with.

Based on the frequency, I'm thinking it's from one of the 3-phase supplies, but I haven't really dug into It yet.

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radioman1992
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Re: Collins Power Rock Audio Hum??

Post by radioman1992 » Thu Oct 13, 2016 6:33 pm

Thanks Guys for the insight, I'm gonna get back up there and do some more checking.. I will report any advance made on this subject, interested to scope it and see what i see!
:D

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radioman1992
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Re: Collins Power Rock Audio Hum??

Post by radioman1992 » Thu Nov 24, 2016 12:05 pm

So I am Glad to Report that the hum is gone :D I pulled the power supply card from the transmitter and found some really dried out caps.. "2 1000uf 25v and 1 1000uf 50v electrolytic caps" 5 mins and 6 dollars later, we are back and quite.. thanks for all the insight you guys give on this page

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