Yamaha MX-1000 repair

RichWare

New Member
Hello,

I am new to this forum, I am living in Holland and I own a Yamaha MX-1000 for about 20 year. I like it very much although it is a bit to heavy proportioned for use in the livingroom. The sound is realy great!

Last weekend suddenly it stopped working: I switched off a light and a loud bang came out of the speakers. It went into protection and I did smell a odor of burning electronics.:worried:

I found some information on the internet like a service manual, schematic and this great forum. So I thought let's give it a try, I have a soldering iron, multimeter and an education in electronics.

I measured the tensions on both amplifiers and found out that the right schannel is broken. The multimeter on IN and OUT meassured -86 Volt.

So I removed the right amplifier from the powersupply and the protection led went normaly out after two seconds.
I saw that all of the transistors Q318 / Q328 (even numbers) in the I-Amp block are damaged (shorted) and most of the resistors R272 / R382 (even numbers) on the collectors are burned (open).

I have some questions, I hope someone can answer:

What is the best way to repair this amp? Do I have to replace the broken parts and connect the amp to power supply and see what will happen or shoud I first remove more transistors and other parts to measure them? What is the best order to fix this amp?

What more is probably broken as a result of the shorted I-Amp?
Where do you recommend to buy replacements?

I read some thing about Sony bond glue, is there a need to remove it?

I hope that you can help me.

Thanks in advance!
 
Hello !

Welcome on AK !

I think you better send the defect channel to somebody who knows perfectly what he is doing .

I you miss some bad component , put the channel in place and after switch the power on , you take the risk of big surprise ...again ...

This is my point of view but you can try if you want ...Beware of the final invoice ...If you are not successfull :yes:
 
Welcome to AK!
I second Clinic-Audio's advice to take it to a pro.

If you still want the pain, then I would start by checking every component on that bad amp. Check all transistors out of circuit. The drivers are most likely gonne as well. The power supply trannies (2sc3281, 2sa1302) will appear shorted in circuit but may be fine otherwise. The white glue on the MX-1000 is not corrosive, nevertheless, I removed it on mine. The M's have the corrosive glue issue.
One of the reasons these amps fail is cold solder joints. I would re-solder all joints on all boards before you put it back toghether. I re-soldered all joints on mine, except on the meter section.
Servicing this particular amps is somewhat cumbersome given its internal design; how the sub-circuit amp boards are attached to the main board. I took Avionic's advice and made a jig to help me work on it. I would strongly suggest you do the same. This will help you prevent accidents that can cause additional damage.
I would replace all output stage trannies. Once you change the bad ones, the old ones that are still good may fail shortly after. Do not buy "original" Toshiba trannies off of e-bay or other questionable sources. They will most likely be fakes since the original Toshibas are discontinued for a long time. There are reliable places from where you could get good replacements / substitute parts. Do additional research on this forum. Here is a taste of the pains I had to go through: http://www.audiokarma.org/forums/showthread.php?t=602776&highlight=mx-1000

I am not a pro and the advise I have is limited, but if you ran in specific issues, there are folks on this forum that are very knowledgeable.

Good Luck!
 
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DSBG (Dreaded Sony Bond Glue) disease could be an issue in the MX-1000.

See my sig for links.

While it's not likely the cause of your catastrophic failure, it needs to be addressed as part of the repair.
 
Thanks for your advice.

Sure I am not a pro but I like to take the pain.
I am going to check every component in the broken chanel.
I will relace all the power transistors.
@ rottalpha: wat do you mean by " took Avionic's advice and made a jig to help me work on it." What is a jig?

Regards, RichWare
 
"Jig" in this case just means a special tool/fixture to make a job easier or less risky. I do not know the specifics of it but I presume it is a holding device of some sort that frees up your hands to do the tests or repairs.
 
"Jig" in this case just means a special tool/fixture to make a job easier or less risky. I do not know the specifics of it but I presume it is a holding device of some sort that frees up your hands to do the tests or repairs.

yes a fixture. I used a plywood board to anchor and support the boards separate and not moving. Others may have a different method.
I used jumpers so that I can keep the boards apart and get access to all components, plus be be able to test them before finally punting them back together. Be ware to not overheat the main board / sub-boards junction soldering pads.
You need to test the main board in circuit with the sub-boards attached. I found that if testing the main board separate, with no load, the voltages on the LB rail get dangerously close to the 40,000uf main caps limit of 50v. The LB under load should be way lower than 50v. See my post on this issue.

Brutal's advise is to address the glue issue and he definitely has more experience than I do.
I could be wrong about the glue in the MX-1000. However, I have two amps and found no corrosion in either one. I searched the web for other MX-1000 board photos and did not see signs of corrosion. But again, I could be wrong and this is one of the precautionary reasons I removed it on mine.

I know that the M series (M-85, M-80, M-70..etc) have the infamous Sony glue that is corrosive. The MX-1000 glue appears to be a different type of glue. Removing it is not that hard.

Use a heat gun to lightly heat up the glue (be careful not to overheat). This glue unlike the older brownish Sony glue is still very elastic when worm. Scrape it with a piece of hard plastic or something that will not scratch your board (I scratched the silk screen on mine by using a small flat screw driver..not recommended), then use alcohol and q-tips to remove the rest. Some may have different methods, but this is what worked for me. In my amps, none of the components buried underneath the glue were affected. Tested them all out of circuit and were all fine. I replaced all electrolytic caps out of precaution. Be ware that if you opt to change the caps on yours, some are bi-polar. All available from Mouser or the other major vendors.
 
I did search for de Toshiba 2SA1301 and 2sc3280 and found out that the originals are not available anymore, I saw them on sites like eBay and aliexpress. Do you know if these transistors are reliable or do I need to buy replacements?
Are the replacements for the 2SA1301 (2SA1943), 2sc3280 (2SC5200) and other transistors in the MX-1000?
 
on eBay and aliexpress, you will most likely find fakes, since the original trannies are out of production since the 90's.
Buy the Toshiba replacements (2sa1943/ 2sc5200) or the onsemi's MJL1302/ MJL3281 and replace all output transistors on the bad channel. Look for them at B+D, Mouser, Digikey. They are fairly inexpensive and have a higher heat dissipation rating than the originals.
 
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I know that the M series (M-85, M-80, M-70..etc) have the infamous Sony glue that is corrosive. The MX-1000 glue appears to be a different type of glue. Removing it is not that hard.

Use a heat gun to lightly heat up the glue (be careful not to overheat). This glue unlike the older brownish Sony glue is still very elastic when worm. Scrape it with a piece of hard plastic or something that will not scratch your board (I scratched the silk screen on mine by using a small flat screw driver..not recommended), then use alcohol and q-tips to remove the rest. Some may have different methods, but this is what worked for me. In my amps, none of the components buried underneath the glue were affected. Tested them all out of circuit and were all fine. I replaced all electrolytic caps out of precaution. Be ware that if you opt to change the caps on yours, some are bi-polar. All available from Mouser or the other major vendors.

So, about the DSBG issue in some Yamaha gear, is any Sony gear actually affected or was it just a nefarious play on Yamaha by Sony with the glue? :scratch2:
 
yes a fixture. I used a plywood board to anchor and support the boards separate and not moving. Others may have a different method.
I used jumpers so that I can keep the boards apart and get access to all components, plus be be able to test them before finally punting them back together. Be ware to not overheat the main board / sub-boards junction soldering pads.
You need to test the main board in circuit with the sub-boards attached. I found that if testing the main board separate, with no load, the voltages on the LB rail get dangerously close to the 40,000uf main caps limit of 50v. The LB under load should be way lower than 50v. See my post on this issue.

Brutal's advise is to address the glue issue and he definitely has more experience than I do.
I could be wrong about the glue in the MX-1000. However, I have two amps and found no corrosion in either one. I searched the web for other MX-1000 board photos and did not see signs of corrosion. But again, I could be wrong and this is one of the precautionary reasons I removed it on mine.

I know that the M series (M-85, M-80, M-70..etc) have the infamous Sony glue that is corrosive. The MX-1000 glue appears to be a different type of glue. Removing it is not that hard.

Use a heat gun to lightly heat up the glue (be careful not to overheat). This glue unlike the older brownish Sony glue is still very elastic when worm. Scrape it with a piece of hard plastic or something that will not scratch your board (I scratched the silk screen on mine by using a small flat screw driver..not recommended), then use alcohol and q-tips to remove the rest. Some may have different methods, but this is what worked for me. In my amps, none of the components buried underneath the glue were affected. Tested them all out of circuit and were all fine. I replaced all electrolytic caps out of precaution. Be ware that if you opt to change the caps on yours, some are bi-polar. All available from Mouser or the other major vendors.

Haven't actually seen inside an mx1000, just assumed - wrongly I suspect.



Sent from my subconscious mind.
 
work in progress

Thanks for your help and advice, I am still in the process of checking the components.
Which capacitors shoud I replace: the electrolytic, ceramic or film?

It seems that half of the power transistors are broken / shorted and also some of the drivers.
I am planning to replace all transistors accept the four dual transistors in the HCA. They test oké and are almost unavailable.
The power tranies 2SA1301 I'll replace for the stronger / cheaper 2SA1943 and the 2sc3280 for the 2SC5200.
I'll buy the originals at B+D and the replacements at Mouser.

To be continued.:thmbsp:
 
DSBG (Dreaded Sony Bond Glue) disease could be an issue in the MX-1000.

See my sig for links.

While it's not likely the cause of your catastrophic failure, it needs to be addressed as part of the repair.
Hello brutal,

The glue in my MX-1000 looks like it is not corrosive, shall I leave it like it is?
 

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It seems that half of the power transistors are broken / shorted and also some of the drivers.
With that kind of damage. There is bound to be a handful of burnt up resistors , diodes and even capacitors.

As to your question about cap replacement-- electrolytics:thmbsp:

I have not seen any of the troublesome glue in the MX1000. Just the rock hard white bonding adhesive.

If you don't have to mess with it . I'd leave it be. I have seen no evidence that it causes corrosion or oxidation.
 
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Hi avionic,

With that kind of damage. There is bound to be a handful of burnt up resistors , diodes and even capacitors.
Four of the power trans collector resistors where burnt.
What I don't understand is how it's possible that the IN as well as OUT both measured -86 V !

Should I replace (zener)diodes also?

What do you think about replacing the transistors for other types?
Some of them are not available or almost not, I just found out that there is only one pair of 2SA1302 and 2sc3281 at D+B.
At D+B Ihave to pay $50 for shipping, Mouser and Digikey have settlings in The Netherlands.

When you know good and recent replacements for the transistors on this amplifier board, can you lease name them?

Thanks in advance :thmbsp:
 
Four of the power trans collector resistors where burnt.
What I don't understand is how it's possible that the IN as well as OUT both measured -86 V !

Should I replace (zener)diodes also?

What do you think about replacing the transistors for other types?
Some of them are not available or almost not, I just found out that there is only one pair of 2SA1302 and 2sc3281 at D+B.
At D+B Ihave to pay $50 for shipping, Mouser and Digikey have settlings in The Netherlands.

When you know good and recent replacements for the transistors on this amplifier board, can you lease name them?

Thanks in advance :thmbsp:

I think I mentioned to you that the power transistors need to be tested out of circuit. I am not saying that they are good or bad, but for certain they will be testing as bad / shorted, if tested in circuit.

The output transistors are the ones that are most likely burned if they tested bad in circuit.

at a minimum, change all electrolytic caps the amp sub boards; replace C511 on the main board.

The glue will clean up fine if you have patience. See my previous suggestion on how it can be done. If you do not plan on changing those caps, then leave it alone. If you change the caps, then cleaning the glue makes sense.
 

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