MX-1000 rebuild

[amr2]

I have no luck so far. I have checked every component in the HCA and I-AMP sections, and replaced the bad components (Q309,311,313,315, D333 and a few resistors). I used dummy resistors instead power transistors.
On first power up, the output and input voltage on the sub boards was not cero, and transistors Q309,311,313,315 gets hot. Without the "IN" and "OUT" wires conected (to isolate the sub-board from the V-AMP) it doesn't work either. Finally Q309,311,313,315 have burned again...
.

 

[rottalpha]

I have no luck so far. I have checked every component in the HCA and I-AMP sections, and replaced the bad components (Q309,311,313,315, D333 and a few resistors). I used dummy resistors instead power transistors.
On first power up, the output and input voltage on the sub boards was not cero, and transistors Q309,311,313,315 gets hot. Without the "IN" and "OUT" wires conected (to isolate the sub-board from the V-AMP) it doesn't work either. Finally Q309,311,313,315 have burned again...
View attachment 848691 .

I feel your pain.
Did you check the small 6.3v caps on the main board? I believe they are 100uf. They are most likely shot.
Check all resistors in that region. I am assuming you have checked all semis on the main board, including the germanium diodes. Sorry for not naming exact components. I am traveling.
I had a similar issue with on of mine and one of the resistors burried under the glue and a few of those diodes were toast. The 6.3 v caps were testing in pF range.

 

[amr2]

I'm going to check the main board again.
I like the idea of checking the sub-board without the v-amp section, to try to isolate the problem. I think that just connecting the power cables, and putting an input resistance to ground should work...I have to think about it.

 

[amr2]

Q513, Q515, D507, D509 and D511 (V-AMP) were changed recently, and they are probably counterfeits. C517 (100uF / 6.3) is measuring pF.
I'm going to change these parts, and I think I'm going to use 1N4148 for the 1SS133 (is there any better option?)

 

[rottalpha]

You can change most semis in mx-1000 with modern replacements. I am not in town and I am away from my notes. Wait for Dave to chime in.
I a m glad you spotted that cap. Change all three with higher voltage ones. There's plenty of room.
Also look for burnt resistors.

 

[avionic]

1N4148 more than adequate for the 1SS133.

 

[amr2]

You can change most semis in mx-1000 with modern replacements.

Yes, that is just what I'm doing.
I'm going to replace all electrolitic caps (except the 4 big "cans"), most of them are out of specs.

1N4148 more than adequate for the 1SS133.

Perfect, thank you!

 

[amr2]

Please can anybody tell me the correct value of these pair of resistors? They are in series with the 820uF capacitors. The top pair have been changed (2x2R2), the bottom one seems original (2x10R). The schema shows one only resistor of 1R.

 

[rottalpha]

Please can anybody tell me the correct value of these pair of resistors? They are in series with the 820uF capacitors. The top pair have been changed (2x2R2), the bottom one seems original (2x10R). The schema shows one only resistor of 1R.

View attachment 850029

I cannot help you with the value, but can tell you that the green ones are the original ones, so use them for reference (if they are not fried). Yes, there are some updates Yamaha did to these boards, without providing any official service bulletins, at least none I was able to locate within the past few years.
Because you have a newer build and the schematic is that of the original build, you will see such differences. Replace with what's original on the board.
I just did some work on one of my MX(s) and I have some photos on my phone. I always take lots of photos

 

[rottalpha]

Can you make out the colors off of this?

They look like 10R

 

[avionic]

brown/black/gold = 1R

 

[rottalpha]

brown/black/gold = 1R

eagle eye to the rescue

 

[amr2]

the green ones on my board are the same as yours. The colors seems to be black-brown-gold but they measures 10R.

 

[avionic]

Not eagle eye.. Eagle Keeper...

 

[avionic]

The colors seems to be black-brown-gold but they measures

Looks like brown/black/gold to me.

 

[amr2]

Sorry I wanted to say brown/black/gold. But both measures 10R not 1R.

 

[rottalpha]

Sorry I wanted to say brown/black/gold. But both measures 10R not 1R.

it looks like gold, but you never know what goodish gray that is LOL. Try another meter and if they still test 10R, replace them. Sorry I cannot provide a measurement. I am over a couple of thousand miles away from that thing.

Not eagle eye.. Eagle Keeper...

Yes Eagle Keeper Sir! it will not happen again

 

[amr2]

New parts placed. The drivers gets very hot within seconds, and the output voltage is not cero. Something is still wrong.
I'm going to use a large dummy resistor (>1K) to limit more the current and be able to measure...

 

[amr2]

and perhaps the feedback network is oscillating

 

[rottalpha]

man that sucks!

were you able to test the main board without the subs installed?

Also, please help me understand. Re:

I used dummy resistors instead power transistors.

Do you mean the output transistors or power transistors?

you have 6 output transistors and 4 power transistors for each channel. I am sure you can ran the amp without the output transistors when you place the resistor load instead, but can you do the same about the power transistors?

Also, I am assuming you are doing one channel at the time.
You can work one channel at the time and the main board voltages should be good (given that nothing is wrong with the main board) you do not need both sub boards connected. One board is enough to load the PSU for both channels and the voltage on the main rails should not be wonky.

on the sub-boards; when your pre-drivers an drivers got toasted last time, did you check that 1watt zenner right in front of them? That zenner most likely went kaput as well.

Are you powering up with a DBT?