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MX-1000 rebuild

amr2

amr2

Well-Known Member
Hello

A very abused MX-1000 is on the bench. Two techs have been working on it and now the amp is a complete disaster. Broken traces, several fake transistors, missing parts...

I have removed both APS boards, because I want to test the power supply and V-AMP sections first. The power supply measures OK, but the output of the V-AMP is -94V on both channels.

Have anyone tested this amp without theese boards?

Thanks
 
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I had to fashion a jig to hold the board and then make the proper connections with umbilicals fastened to there proper locations.
 
The problem is the V-AMP output not conected to the NFB loop without the APS boards. I attached a 1K resistor from the V-AMP out to the NFB input, and the output drops close to 0, but the resistor gets hots and the output waveform is wrong (the input is feeded with 1KHz sine wave). VAS transistors and diodes measures fine.

I will connect the APS boards as you suggest Dave.
 
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amr2 said:
Have anyone tested this amp without theese boards?
Click to expand...
I can tell you for a fact that without the sub / amp boards, the main board voltage at the filter capacitors will be wonky. At 94V you are well passed the spec of those cans and are looking at a bigger problem if they go bad.
 
I think that the maximum voltage at the filters caps are not reached. With HB=94V and LB=42

C537-538 50V max -> 42V
C535-536 63V max -> 94-42=52V
 
Yes, I can remember it. The problem is that without the APS boards LB is working with no load, and thus the voltage is higher than expected (48V in my case). If you put a load resistor between + LB and -LB the reading is correct (about 42V) without the APS boards. HB measures always OK because it's always loaded (it supplies the voltage to the V-AMP section).
 
Definitely the V-AMP doesn't work well without the APS boards. I have tested it with one of them like Avionic suggested, and it seem to works well now. The other APS board needs more work...there are several counterfeit transistors, broken tracks...

Apart of this, the meter and the lights doesn't work, and the speaker plugs are broken...
 
amr2 said:
The other APS board needs more work...there are several counterfeit transistors, broken tracks...

Apart of this, the meter and the lights doesn't work, and the speaker plugs are broken...
Click to expand...

I feel your pain.

About the meter...is it just the light or the meter itself? You would not see anything on the meter if the lights are bad. You can shine any type of light through the back openings of the meter. If the meter itself is still working, you would know.

That said, I do have a meter here where the meter is actually compromised. I hope it is just the lights with yours.

On the speaker posts board, there is a cap that was replaced in later units. I can't recall exactly which it is, but depending of your serial number, it will not match the schematic. Heads up when recapping.
 
rottalpha said:
About the meter...is it just the light or the meter itself?
Click to expand...

I have to check it

rottalpha said:
On the speaker posts board, there is a cap that was replaced in later units. I can't recall exactly which it is, but depending of your serial number, it will not match the schematic. Heads up when recapping.
Click to expand...

I didn't know it, thank you! About the recap, does anyone have any recommendations about what capacitors to use?
 
I
amr2 said:
I have to check it



I didn't know it, thank you! About the recap, does anyone have any recommendations about what capacitors to use?
Click to expand...
I use nichicon kz. Use muze for the bi-polar.
You can clean the glue while you're in there, but it is not necessary....not corrosive on the MX amps. I found that using a heat gun to get it a bit warm helps a lot. Use a a hard plastic to scrape it off. It comes off quite easy. Use rubbing alcohol for final clean off.

What is your serial number?

Yamaha has made some updates to the circuitry for mid E02...and later. No service bulletins to document it.
 
rottalpha said:
What is your serial number?
Click to expand...

E039309RT

What about something like this?

APS and PS boards:

Bipolars -> Nichicon ES
Muse polar, blackgate -> Nichicon FG. FW or KW if voltage is not available.
For the 820/110V, perhaps UCC KYB

Speaker Binding post capacitors:
Some general purpose capacitors.
 
amr2 said:
E039309RT

What about something like this?

APS and PS boards:

Bipolars -> Nichicon ES
Muse polar, blackgate -> Nichicon FG. FW or KW if voltage is not available.
For the 820/110V, perhaps UCC KYB

Speaker Binding post capacitors:
Some general purpose capacitors.
Click to expand...
Based on your serial number, you have the latest boards revisions
I like nichicon and I use them when they are available.
 
amr2 said:
E039309RT

What about something like this?

APS and PS boards:

Bipolars -> Nichicon ES
Muse polar, blackgate -> Nichicon FG. FW or KW if voltage is not available.
For the 820/110V, perhaps UCC KYB

Speaker Binding post capacitors:
Some general purpose capacitors.
Click to expand...


Did u start putting it back together?
 
No, I'm still working on the bad channel. I have to order some parts to replace the counterfeits.
 
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