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Old 14th January 2007, 07:26 PM   #1
Zorac is offline Zorac  Canada
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Default yamaha m-50 repair

I have a yamaha m-50 I am trying to repair, anatec has been helping me on another forum (and instrumental in me getting as far as i have!) and suggested i post up here as well, so ill post up its problems, and what ive tried, and see if anyone has any other ideas!

the problem is as follows
-protection clicks on when the levels are turn above 4
-happens regardless of input level/type (input is via a htpc)
-test on 3 different sets of speakers, same result
-amp is drawing approximately .5 amps of power when in use, the same amount of power my other 4 amps are pulling combined (m-80, m-45, fosgate m100)

i have replaced a cap in the protection circuit (c-145), which had no affect. i then proceeded to try and calibrate it based on the service manual

here is the calibration chart from the manual
http://miniunit.com/user_uploads/Zor...alibration.jpg

with an input of 118.8v i had 62.1v (suppose to be 65.5) for step one, and 2.8v (suppose to be 1.0) for step two.

adjusting vr601 had negligible effect, so i left it in the middle, adjusting vr602 had a very small effect, the original reading was 3.2v for step two and by adjusting it all the way down i could only obtain the 2.8v

i then proceeded to use the power trouble shooting page from the manual, although i dont have a variac, i was able to do some of the tests

here is the testing procedures:
http://miniunit.com/user_uploads/Zor...erdiagnose.jpg

for the first procedure they gave a reference for 120vac (which should give a reading of 5.5vac and i measured 8.7vac on my amp with input voltage being 120.2vac) and the second procedure is the same as the second calibration step, which i already knew is reading way high.

as i understand, in these circuits, the electrolytic caps are generally the first thing to go, and being only two of them, ill replace them, and with the first trouble shooting procedure indicating a problem, ill replace the src/triac/control ic as well.

for reference, the power control circuit
http://miniunit.com/user_uploads/Zor...trol_board.jpg

i am working on access to a variac so that i may probably perform the troubleshooting procedure.

i would appreciate any ideas/help/procedures to help me narrow down the problem!!

keep in mine, although im comfortable working on the amp, know what all the basic components do, i have no clue when i come to interpreting a circuit.

thanks!
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Old 14th January 2007, 07:57 PM   #2
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Try to hook up with no load at first to see if you get the same result.Then load up one channel at a time to see if we can isolate the left or right channel.
For reference a M-45 has two 22,000 ufd @ 71vdc -yamaha p/n V6512400 in the power supply thru Yamaha they are around $30 ea.
Dave
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Old 14th January 2007, 08:55 PM   #3
Zorac is offline Zorac  Canada
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for a load, i assume just plug in a speaker? and i would guess i need to use an input signal as well into the amp?

any value in particular i should be watching? or just take the two readings that i was using for adjusting?
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Old 14th January 2007, 09:23 PM   #4
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Yes I was refering to the speakers,If you have a signal generator 1khz input will work . If no generator, any sound source will do.
The only monitoring required is your ears.What I was going for was to try and determine 1.) If the protect engages with no speakers hooked up. 2.) Engages with either the Rt or the Lt. You stated that turning the volume up beyond 4 and the protect engages....So with no speakers attached turn the volume up beyond 4 and so on with a speaker on one channel and then the other. The protect circuit may or my not be operating correctly.
Dave


P.S. If possible could I get a copy of the schematic. The closest I have is a M-45 and judging by your already posted partial diagrams it is way different.Especially the power supply.
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Old 15th January 2007, 01:06 AM   #5
Zorac is offline Zorac  Canada
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i know it will do it with no load, thats first thing i check, as a blown speaker would do this, so i unplugged the speakers and had the same result, i will test further to see if changing where the input is applied (l or r) has an affect.


edit:

i did some further testing, it doesnt not seem to be left or right related.
with a signal (input) on both l and r, and a load on l, r, both, or neither results in the protection coming on.

with a signal on the l input only, and a load on the l only speaker, the protection wont come on. with a signal on the r input only, and a load on the r only speaker, the protection wont come on.
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Old 15th January 2007, 01:06 AM   #6
Zorac is offline Zorac  Canada
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here are the schematic, be warned, its about 100mb for all 3


http://miniunit.com/user_uploads/Zor...%20Pg%2012.JPG
http://miniunit.com/user_uploads/Zor...%20Pg%2013.JPG
http://miniunit.com/user_uploads/Zor...%20Pg%2014.JPG
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Old 15th January 2007, 10:01 PM   #7
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Zorac
I can not open the last of the schematic files
http://miniunit.com/user_uploads/Zo...M%20Pg%2014.JPG
can you? Does it have the actual schematic


This is interesting
Quote:
with a signal on the l input only, and a load on the l only speaker, the protection wont come on. with a signal on the r input only, and a load on the r only speaker, the protection wont come on.
...Do you get good audio sound or is it distorted? Any leads on a variac?
Dave
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Old 15th January 2007, 11:20 PM   #8
Zorac is offline Zorac  Canada
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try opening it in 'windows picture and fax viewer' (you can get to it in winxp by doing a right click on the file and selecting preview). i know alot of other programs dont like it due to the size. the full size is 56.0 MB (58,792,934 bytes) for pg 14. pg 14 is the full schematic. i checked my server, and its all there.

no variac yet. the guy who i though might have access to one, turns out they dont have one in their shop. so im watching ebay, cheap ones without a case go for fairly cheap. wouldnt take much to wire one up and build a case.

the audio when testing one side at a time was clear, i wasnt listening specifically for distortion, but i didnt hear any either. i would of noticed though if there was any appreciable amount.
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Old 17th January 2007, 05:01 AM   #9
mikeks is offline mikeks  United Kingdom
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Zorac, it would be helpful if you reduced the size of the schematic by saving, say, as .png.
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Old 17th January 2007, 10:01 PM   #10
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Zorac
We finally got it down loaded..
Dave
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