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DC PRT 000 Yamaha RX 457

 
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duke



Joined: 11 Oct 2010
Posts: 17

PostPosted: Wed Feb 09, 2011 10:05 pm    Post subject: DC PRT 000 Yamaha RX 457 Reply with quote

Hello,

got a broken RX V 457.

Sometimes its starting fine, sometimes only in protect mode override.

Anyone got an idea, what I could be.
If I measure on the speaker connector, I mostly measure DC smaller than 10mV, except one channel. It has more.

Anyone has an idea how to continue to fix this problem?

thx

regards
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Justmanuals



Joined: 21 Aug 2004
Posts: 1949

PostPosted: Thu Feb 10, 2011 1:26 am    Post subject: Reply with quote

This Parts & Service manual can now be purchased for $11.77 and downloaded immediately after payment from
http://www.justmanuals.com


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jts1957



Joined: 24 Nov 2008
Posts: 2472
Location: Far, Far Away

PostPosted: Thu Feb 10, 2011 2:31 am    Post subject: Reply with quote

FREE service literature

http://elektrotanya.com/?q=showresult&megnev=&megnev2=%20RX%20V%20457&kategoria=&kat2=all
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duke



Joined: 11 Oct 2010
Posts: 17

PostPosted: Thu Feb 10, 2011 6:38 pm    Post subject: Reply with quote

got already sm, anyway thx
seems that you both are not the best friends Confused

anyway, back to my problem.

self diagnostic: dc prt 000 means that is has 0mV voltage, so i should be ok??

i measured all channels, all are below 10mV except one surround.

anyone has some tips how to solve the stuff?

sometimes the receiver works fine, sometimes it shuts of itself.

thx.
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Thu Feb 10, 2011 8:55 pm    Post subject: Reply with quote

Duke,
(strictly working out of memory since I've been out of Consumer Electronics for some time)
When you are doing the diagnosis, you should not see protect of any kind? If I remember right, the "000" was meant as a percentage indicator and it may not actually register the DC value(if it happened to be small or on the border line).
After clearing the events, you should not see any "dc prt" regardless.
I believe the lonely surround channel may in fact be the triggering culprit.
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PostPosted: Thu Feb 10, 2011 9:45 pm    Post subject: Reply with quote

what do you mean by:
When you are doing the diagnosis, you should not see protect of any kind?

i have to start in the protection cancel diag mode, that it will not turn off.

yes, 000 indicates the level, where 100 % means 5V, written down in the SM.

dont know, how far the ADC can measure. But 600mV is not so small, about 10% from 5V. Should be no Problem for a 10 bit ADC, i guess. dont know how it is measured, but 600mV is almost enough for a transitor.

So we agree, this surround channel is faulty.
Still the question, sometimes after start it doenst turn off itself, running and i can measure the 600mV.

But how do I continue, to fix this channel?
In SM it is written to cut the bias resistor for this channel....
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Thu Feb 10, 2011 10:32 pm    Post subject: Reply with quote

Do not remember how the translation is done but i can tell you that 600mv is WAY too much. as a matter of fact the threshold is around 10~15 mv (page 45) and obviously anything over that WILL trigger the protect. let me take a look at schematic. I do see the resistor removal procedure but it was mainly intended after a channel repair where tolerances of replacement parts may not exactly match.
What you need to do is to backtrack and try to localize the problem first. The "extra" voltage could be anything from a leaky cap or transistor along the way all the way up to the front end. Also, look at page 86; that is where the protection circuit is located. The PRT line is sampled from each channel and sent to the processor. The plus/minus readings on the base of the output and driver transistors are critical. I have run in to similar situations and it is not always easy to locate the culprit.
Another tip is to utilize a similar good channel as a reference(of course in the off mode) and do resistance checks on various spots along the circuit for comparison against the bad channel. On many occasions, it can lead you to the offending component(s).


Last edited by vtech on Sat Oct 05, 2019 5:29 am; edited 1 time in total
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duke



Joined: 11 Oct 2010
Posts: 17

PostPosted: Wed Feb 16, 2011 4:30 pm    Post subject: Reply with quote

Ok thanks so far vtech.

Last days I didnt have the time at work to look for it.

Yeah, 600mV is not less. Thats the reason, why I was supprised that the V457 sometimes work and doesnt enter the protect mode.
Maybe one problem additional to this.

But I will try to fix this one first and look then, if it always works fine after repair.


Anything from leaky cap or transistor....hm, sound like I have to disassemble the unit to see clear on the pcb.
Thanks for the tip, good idea. May I can also try to measure voltage on certain points to figute out any difference.
Keep you informed, probably, next days or week.

But thanks so far for some ideas.
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