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Deepdark

Re: LA2A Issues
« Reply #20 on: October 06, 2014, 04:35:44 PM »
check that post too, talking about how bad capacitor may sound. http://groupdiy.com/index.php?topic=47018.msg590696#msg590696
"I'm givin' you that money so I don't have to kill your ass."


Alrod

Re: LA2A Issues
« Reply #21 on: October 08, 2014, 06:23:12 PM »
I am having a local amp repair guy look at it.  I just don't have the skill set for troubleshooting the caps.

Deepdark

Re: LA2A Issues
« Reply #22 on: October 08, 2014, 07:58:27 PM »
Let us know :)
"I'm givin' you that money so I don't have to kill your ass."

Alrod

Re: LA2A Issues
« Reply #23 on: October 09, 2014, 06:43:56 PM »
I took one last look to see if I missed anything before taking it the LA2A to the repair shop.  My unit has a 9k Ohms 5% resistor between the R29 and the CR1.  I noticed that the resistor is charred.  So two questions:

1.  Could this be the cause of my problems?

2.  I noticed that this particular resistor does not exist on the schematic you posted.  What happens if I remove it?  In other words can I use it that way at least temporarily without blowing anything up?
« Last Edit: October 09, 2014, 07:26:39 PM by Alrod »

Deepdark

Re: LA2A Issues
« Reply #24 on: October 10, 2014, 06:43:32 AM »
You can try to replace it. I don't know why they put this resistor. Maybe to tweek the voltage for a decent value. I don't know.
"I'm givin' you that money so I don't have to kill your ass."

Alrod

Re: LA2A Issues
« Reply #25 on: October 10, 2014, 05:23:16 PM »
Here is an update on the resistor.  It is actually a 1k ohm resistor.  Although the one in my unit was a 1/2 watt, the tech at Universal Audio said I should replace it with a 1k ohm 2 watt.  He also stated that i should replace it with a carbon composite resistor.

The resistor in this position is found only on UA LA-2a's (not older Teletronix units), it serves to reduce the inrush current surge and extends the life of the 1st power supply filter capacitor and the rectifier diodes. Prior to heat discoloration, the color code on the resistor was brown, black, red, gold.   This has been confirmed, so it is definitely a 1k ohm.

What is a good source for carbon composite resistors?
« Last Edit: October 10, 2014, 10:03:32 PM by Alrod »

Deepdark

Re: LA2A Issues
« Reply #26 on: October 10, 2014, 09:27:06 PM »
Mouser, digi key, Newark,  etc.  :)
"I'm givin' you that money so I don't have to kill your ass."

Alrod

Re: LA2A Issues
« Reply #27 on: October 11, 2014, 05:37:42 PM »
What is your recommendation for a C7A and C7B? replacement cap? A parts list I found on ProAudio.rec lists a UVZ2W470MHH. According to Mouser and Digikey, this part is "obsolete". I get confused with the 'VZ', 'VX', 'VR', markings. The two on my unit are marked 'VR(M)'. One of them has a slight budge on the top, so i would like to replace it if for nothing else, peace of mind.

Deepdark

Re: LA2A Issues
« Reply #28 on: October 11, 2014, 09:02:13 PM »
Is it the 33u or the 47u? Anyway, anything rated for at least 400v and in the nichicon, panasonic, vishay, cornell dubilier, etc. Will be fine
"I'm givin' you that money so I don't have to kill your ass."

Alrod

Re: LA2A Issues
« Reply #29 on: October 27, 2014, 11:06:23 PM »
All is well with my unit now.  I replaced the 1k ohm resistor, and the LA2A is working perfectly.  It actually does not need the 47uf 450v caps replaced, but i bought a few spares just in case. 

What an outstanding piece of gear!
Thanks 'Deepdark' for all your help!  I am toying with the idea of building a DIY version.


Deepdark

Re: LA2A Issues
« Reply #30 on: October 28, 2014, 10:41:12 AM »
It was a pleasure. Glad to see that everything is working now. Yes it's an outstanding beast once you found its sweet spot. It's really easy to diy, just take your time and go slowly :)
"I'm givin' you that money so I don't have to kill your ass."


 

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