NAD 5420 CDP STA341M overheat - diyAudio
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Old 28th August 2010, 01:43 AM   #1
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Default NAD 5420 CDP STA341M overheat

I have a NAD5420 cdp that IC506, STA341M gets very hot and cd stops playing.

Voltage supply to STA checked normal +/- 15V.
Cleaned spindle and sled motor, tested 5.9v current looks good, but no improvement.
New STA replaced, same thing.
Anyone can help here?

Last edited by fastvideo; 28th August 2010 at 01:45 AM.
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Old 28th August 2010, 12:13 PM   #2
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It works very well when it is first turn on, then STA becomes hotter and hotter until there is a few ticking noise, cdp stops playing.
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Old 29th August 2010, 01:44 AM   #3
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The first thing I would check is the ac voltage readings on the dc voltage rails to the chip. Failing supply lytics could be dumping too much ac into it. The only other thought I had is that perhaps the platter motor has developed so much carbon buildup that it is drawring excessive current or its brushes may have worn through and are intermittently shorting.
Frankly, though, if this player has the MASH dac that it's listed as having, it's not worth putting much effort into. Those dacs are quite mediocre at best, no matter what you do with them.
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Old 31st August 2010, 03:49 AM   #4
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No one has experience this problems before???
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Old 4th September 2010, 03:28 PM   #5
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No help?
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Old 4th September 2010, 04:57 PM   #6
liquias is offline liquias  Israel
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According to the service manual Q506 is driving the sled motor and the pickup linear servos. You may have some machanical problem in the pickup itself, this may cause the IC to overheat. you can (VERY GENTLY!) lift the plastic cover of the pickup and look for anything that might limit the lens movement. If its not something very obvious, I would return the plastic cap and try to check capacitors C506 ; C503 (1000uF 16V) to see if there is any visible deformation (infalted or leaky). If you have a scope, check dc volatge on these caps as stephensank suggested. If you don't, I would offer to replace them. One important check is to see if the IC runs hot while NOT playing a cd.

If you need a service manual for this model you can get it at HIFI engine.

Let us know what you found.
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Old 5th September 2010, 01:17 PM   #7
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Quote:
Originally Posted by liquias View Post
According to the service manual Q506 is driving the sled motor and the pickup linear servos. You may have some machanical problem in the pickup itself, this may cause the IC to overheat. you can (VERY GENTLY!) lift the plastic cover of the pickup and look for anything that might limit the lens movement. If its not something very obvious, I would return the plastic cap and try to check capacitors C506 ; C503 (1000uF 16V) to see if there is any visible deformation (infalted or leaky). If you have a scope, check dc volatge on these caps as stephensank suggested. If you don't, I would offer to replace them. One important check is to see if the IC runs hot while NOT playing a cd.

If you need a service manual for this model you can get it at HIFI engine.

Let us know what you found.

IC is not hot while cdp is not playing.
Will check the lens later.
I have the service manual.
Thank you for help.
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Old 5th September 2010, 09:07 PM   #8
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When cd is not playing, STA341 is not drawing much current from the power supply, so dying electrolytics(which I am fairly sure you have) may still have enough capacity to have low ac ripple. When cd runs, larger currents are drawn, so dying caps will cause excessive ac ripple to appear. Dying caps will not physically show signs of it most of the time. So, don't assume caps are good just because they look good. Measure ac ripple voltage with cd running.

And, btw, it was VERY rude the way you seemed to dismiss my previous advice out of hand. You don't know that I have 35 years of professional audio service/upgrade experience, but you could have at least been polite and acknowledged my post.
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Old 5th September 2010, 10:32 PM   #9
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Quote:
Originally Posted by stephensank View Post
Frankly, though, if this player has the MASH dac that it's listed as having, it's not worth putting much effort into. Those dacs are quite mediocre at best, no matter what you do with them.
I was very discouraged when I saw this type of reply.
Anyway the second reply is more constructive, thank you.
I will check it out later.
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Old 6th September 2010, 08:01 PM   #10
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Checked capacitors C504 ; C503 (1000uF 16V). clean regulated +/-15v to STA.
Not capacitor problems for sure.
Will try with another lens unit later.
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