yamaha mx 800 led problems please help

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I have a yamaha mx 800 and the center diplay that lights up showing the wats for the power meters didnt work. I discovered the 2 leds were changed to red ones and they were not bright enough. I bought to clear leds from radio shack but every time i hook them up the burn out. I have tried reversing the polarity and the same thing they light up and burn out. Any help would be greatly appreciated.
 
The LEDs u are mentioning may be aged colored bulbs.

Looks like the originals were filament bulbs supplied by a separate winding.
If u want to install LEDs instead, u will have to rectify using brige rectifier and filter the supply, and add a series resistor (R) to each of the led.

How...
measure the ac voltage
multiply by 1.4, this is the dc voltage after filtering. Use about 470µf cap and its voltage more then the calculated.

Each LED drops 1.6 volts.
Vdc minus 1.6/.02 =R for 20mA of LED current

Gajanan Phadte
 
I have drawn a 'schmatic' of the circuit for the Yamaha M-45 which
is very similar if not the same for all the Yamaha amps with the
front power meters.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=110235

The panel is AC lamps in series with resistors, while the LEDs are
driven by rectified DC and driver chips. The lamps drop about 8VAC
while the resistors drop about 3.7 VAC. . .or 123mA per lamp or
about 1W per lamp.

Check out my thread. . .this is all moot if Yamaha redesigned the
lamp circuit for the MX series. . .but I don't think the LEDs when
the MXs were made were that bright. . .

The fact that you installed LEDs in an AC circuit and they worked
briefly and died seems to indicate that it is still an AC circuit. . .that
should drop 8VAC across the lamp, but the LED is lower resistance
and draws too much current and die: either from excessive forward
voltage or too much reverse voltage. . .LEDs don't like AC.

Let's see a pic of the panel you have. . . and compare it to the
M-45. . .
 
The Yamaha M-70 used 14.5V 80mA lamps. All the meters in the
Yamaha amps are similar but not exact: variations include different
driver chips, load select, power ratio change, number of LEDs.

Changing the power ratio is an interesting topic. . .since most
power amplifiers operate at less than a watt when casual listening
is involved. . . changing by a factor of 10 or 100. . .more of the
meter would be used more of the time.
 
You guys are correct

Radio Shack dont carry the filamant bulbs anymore so looks like I am converting them to led's probly better anyway as the life of leds are alot better. I have a pioneer surround sound receiver with low level outs for each channel. the fronts are going to an m-80 that drives my front pioneer cs-905's and cs-605's and the mx-800 I was going to drive the rear speakers which are a set of ar 13's. Watch allot of movies so the amps will be on quite a bit of time. Thanks for all the advice this site is awsome and the people on it are awsome.
 
Here is the mx 800

When I got this amp a week ago it was filthy inside I spent about 5 hours cleaning the inside polishing all the contacts. From what ive read this amp is just as good and clean and powerful as the m80. I just hope I can do the led conversion without messing it up.
 

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Once you pull apart the meter assembly you will be could install
a single diode and extra resistor and LED to convert to LED instead
of lamp. . .if LEDs had been cheaper than lamps when it was first
made, then they would have used LEDs.

The amp should be capable of low impedance loads. . .four caps. . .
the M-45 has only two. . .but same mounting bracket; the M-45 has
the same heat sink brackets that alow narrow main boards in the
M-45 and the wider board for the M-85s.
 
Yes. . .the light source needs to be diffused in order for it to look
illuminated instead of spot lighted. The LEDs in the circuit for the
Power/Class A/Protection board use a LED that has a front pushed
in like a funnel. . .to refract the light to the sides more. The main power
LED is long and narrow, but fairly evenly lit from the round LED; these
LEDs also live in a white reflective housing behind the front of the
unit. Since the reflectors are there for the lamps, you just might
need a LED that is designed for more sideways diffusion. . .alternately
you could use an automotive 12V lamp!
 

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Yamaha M-45/65/85 Meters

The meter lights are filament bulbs, while the actual meters are LEDs. The circuit has several areas and two or three boards. The 12 volts for the circuit and the transistor for turning it on or off could be bad. The LED driver chip could have died. . . I know my meters are sometimes funky and give impossible values. I think the class A on/off transistor sits on the power board also. I rewired one many years ago. You will have to open the front of the amp to get a good look at the boards and check for voltage. But my gut instinct is the LED driver has died. The amp is probably still good. Enjoy those Yamaha amps as long as possible; they may not be perfect, but they were musical. I could probably pull the meter out of my non-working M-45, but it won't have the correct upper range since they were 125wpc instead of the 260wpc M-85s.
 
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