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PA800 distortion and RAM

 
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daveben



Joined: 09 Sep 2015
Posts: 3

PostPosted: Wed Sep 09, 2015 6:38 pm    Post subject: PA800 distortion and RAM Reply with quote

Hi,

I am an electronics engineer attempting to repair a PA800 which has intermittently distorted sound on both headphones and speakers. This forum has led be to believe the RAM is often the culprit for this problem. It certainly sounds like a digital problem as there is all sorts of noise and strange reverby sounds which makes me think the actual audio data is corrputed.

Currently, I have removed the plug in RAM. This seemed to have fixed the problem but, after a couple of days, it has returned.

I can change the RAM chips on the CPU board for new ones but does anyone know for certain if these are really the cause of the problem? One of the threads suggested that, if Korg do the repair, maybe they do more than just replace the RAM. After all, why would the RAM fail unless there was a design flaw elsewhere? On the other hand, the commonest design flaw in this type of application is a timing issue but that would be apparent from day 1.

So, does anyone know if replacing the RAM chips alone might fix this problem, or does anyone have any further information on the cause/fix for this problem.

Thanks

Dave
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AntonySharmman
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Joined: 16 Oct 2010
Posts: 2608
Location: Hellas

PostPosted: Sat Oct 24, 2015 1:00 am    Post subject: Reply with quote

(in PM)
If issue is limited only in user PCM distortion then you've purchased again this defected Ram , so try the
bigger 128 Mb module (only 64 will be used) that is guaranteed working !
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Last edited by AntonySharmman on Wed Dec 02, 2015 7:30 pm; edited 1 time in total
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daveben



Joined: 09 Sep 2015
Posts: 3

PostPosted: Sun Oct 25, 2015 2:33 pm    Post subject: Reply with quote

Hi Antony Sharmman,

I had just about given up on this keyboard but, prompted by your post, today I have spent a couple of hours and measured every resistor pack used in the various data and addresses busses and guess what? I have found 1 resistor in 1 pack which reads 500R but should be 47R! This is in one of the address busses so it could certainly explain the problem.

I am on holiday now for a week but when I return I will replace the faulty resistor pack and see what happens.....Watch this space....

Many thanks

Dave
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daveben



Joined: 09 Sep 2015
Posts: 3

PostPosted: Sat Nov 07, 2015 10:49 am    Post subject: Reply with quote

Antony Sharman you are a hero!

I have fixed the faulty resistor pack and keybaord has now been playing distortion free for several days.

I haven't yet sourced and fitted a suitable fan, that is my next task, but I wanted to say thanks for pointing me to the problem. I never would have thought of looking for that paricualr fault.

Thanks again.

Dave
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alessandro.testa



Joined: 22 Sep 2008
Posts: 2

PostPosted: Sat Mar 12, 2016 8:15 am    Post subject: IMPORTANT - IMPORTANT Reply with quote

Hello guys. IMPORTANT NEWS. Yesterday I fixed my pa 800. I checked a little resistance and after a while one of those which stands around the CPU did not give the appropriate value. I replaced and Go !!!!! No need to spend any money and even change the motherboard. Thank You Dave
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ikromcon



Joined: 27 Feb 2013
Posts: 11
Location: Istanbul

PostPosted: Mon Jul 11, 2016 9:02 pm    Post subject: PA800 distorted sounds at the back Reply with quote

Dear Dave thank you for your sharing, I have exactly the same problem. Tried to format and re-install new OS, but there was very small changes withe noises. After I found your posts I decided to find the defective resistor. just I need your help with the type of resistors and their locations it will be shortcut for me. please appreciate if you can share some pictures.

thank you!
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plhktradoros



Joined: 10 Apr 2018
Posts: 6
Location: greece

PostPosted: Mon Apr 16, 2018 7:31 pm    Post subject: Re: IMPORTANT - IMPORTANT Reply with quote

please i have same problem help me Sad
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