Repairing Yamaha M-80

LeCroy

New Member
Hi guys!
I'm currently repairing a Yamaha M-80 that I would like to restore completely and yes I know that when things go bad with this amp there's a lot of victims, but I took a risk and bought one :D

So the seller said that it powers up, but the protection light stays on. I didn't even power it up after I took a peek inside:
pic 1
pic 2
pic 3
It looks like the right channel is badly messed up by that glue.

So I started taking things apart and making list of components possibly in need of replacements (with the help of schematic of course). I measured power transistors with DMM's diode function and it seems that one power transistor (2SA1169 on main board) is fried (forward voltage only 0.069 V) and one smaller transistor on heatsink (2SC3298A on upper right board) is fried. All transistors on left heatsink seem to be fine.
pic of the heatsinks

The two slim boards look good. The main board looks like this:
overview of main board
So eventually I worked out what components should be replaced and here I have marked all the components I think should be replaced with red:
components to be replaced
I thought that it's better to replace the parts on both channels just to be sure and many of the parts I marked as "to be replaced" look okay, I just think that it couldn't hurt replacing some additional ones. Do you think this is okay or have I missed some components that might be (or usually are) damaged also? How easily do the Mica or Polypropylene Film caps get damaged, is replacing of those just waste of time?

I have some questions about replacement/substitution parts:

Is it okay to replace just the one 2SA1169 and one 2SC3298A from the heatsinks or do I have to replace their complementary pairs also (2SC2773 and 2SA1306A)? I think I need to get the 2SA1169 from ebay to get a genuine Sanken one?

Substitutions for the transistors seem to be hard to find, does anyone have idea of substitutions for 2SC3298A on the heatsink (and 2SA1306A if they need to be changed in pairs) and 2SC3416 - 2SA1352 pairs found on main board?

And can the diodes and zeners be replaced with any part with same properties like:
1S1555 diode => 1N4148 ?
MTZ7.5B zener => any 7.5 V 0.5 W zener ?
HZ16-3L zener => any 16 V 0.4 W zener ?

I hope someone wiser than me can help me a bit so I get this wonderful amp repaired :) I'll be posting pics and stuff as the project goes on.
 
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"Original" Sankens on e-bay are bound to be counterfeit. I'm on the road right now and without access to reference material, surely someone else will come along in the thread and help with subs.

Just about any component that's been touched by DSBG will have enough corrosion on the leads to warrant replacement.
 
And can the diodes and zeners be replaced with any part with same properties like:
1S1555 diode => 1N4148 ?
MTZ7.5B zener => any 7.5 V 0.5 W zener ?
HZ16-3L zener => any 16 V 0.4 W zener ?

Good to go there..:thmbsp:
 
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I think I need to get the 2SA1169 from ebay to get a genuine Sanken one

Fat chance..



Go with a sure bet.
BDEnterprise :thmbsp:

2SC3298A--------Sub 2SD1763A in stock
2SA1306A--------Sub 2SB1186A in stock

2SC2773--------- Sub 2SC3858 in stock Sanken betters OEM
2SA1169--------- Sub 2SA1494 in stock Sanken betters OEM
2SC3416---------------------------- in stock
2SA1352---------------------------- in stock
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4ADRA_enUS448US448&q=bdent
 
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Repairing M80

Hello Lecroy

1S1555 diode => 1N4148 Yes ! :thmbsp:
MTZ7.5B zener => any 7.5 V 0.5 W zener Yes ! :thmbsp:
HZ16-3L zener => any 16 V 0.4 W zener Yes ! :thmbsp:

I don't think that every Japanese TR on EBAY are fake but you can try other lkinks like Avionic found .
Keep us informed about it :thmbsp:
 
Hello Lecroy

1S1555 diode => 1N4148 Yes ! :thmbsp:
MTZ7.5B zener => any 7.5 V 0.5 W zener Yes ! :thmbsp:
HZ16-3L zener => any 16 V 0.4 W zener Yes ! :thmbsp:

I don't think that every Japanese TR on EBAY are fake but you can try other lkinks like Avionic found .
Keep us informed about it :thmbsp:

BD Enterprise is a sponsor of AK. See there banner at the bottom of the page.Ebay is a last ditch (hope I don't get screwed)effort in my book.Akin to NTE..

Although LittlediodeUSA/UK and Activeparts on Ebay I've had good luck with. So far!
 
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Fat chance..



Go with a sure bet.
BDEnterprise :thmbsp:

2SC3298A--------Sub 2SD1763A in stock
2SA1306A--------Sub 2SB1186A in stock

2SC2773--------- Sub 2SC3858 in stock Sanken betters OEM
2SA1169--------- Sub 2SA1494 in stock Sanken betters OEM
2SC3416---------------------------- in stock
2SA1352---------------------------- in stock
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4ADRA_enUS448US448&q=bdent

Is is enough to change only one pair of power transistors and one pair of 2SC3298A+2SA1306A or do I have to change every single one of them? Does one different pair cause problems if all others are originals?
I guess I'll order the parts from B&D as you recommended although it's going to be quite expensive because I live in Finland :(

--- EDIT ---
I placed an order for all of the transistors to B&D.
Just out of interest I also placed some orders through eBay to see what kind of stuff I get from there :D Do you have any ideas how to tell if certain power transistor is genuine or fake? I'm aware of some subtle differences that can tell counterfeit part apart from original such as model number print not being straight but do you have any other clues? I'm even willing to open one to see if the insides match a real one. I bought couple of both of these:
http://www.ebay.com/itm/2SA1169-ORI...243?pt=LH_DefaultDomain_0&hash=item4607c81a9b
http://www.ebay.com/itm/NEW-2SC2773...687?pt=LH_DefaultDomain_0&hash=item3f0ed593d7
I guess I'm still going to use the subsitutes avionic suggested, but I ordered these just because I'm interested if they are fake or not :)

--- EDIT 2 ---
Is it okay to replace electrolytic capacitors with ones that have same capacitance but higher voltage rating? Like replacing 16 V ones with 50 V ones? I think there should no problem as long as the capacitance is same, just wanted to confirm :)
 
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Is it okay to replace electrolytic capacitors with ones that have same capacitance but higher voltage rating? Like replacing 16 V ones with 50 V ones? I think there should no problem as long as the capacitance is same, just wanted to confirm
Yes ..There is probably going to bunch of burnt resistors.Some will look bad and some won't.
Between the copper buss bars that are close to the two large caps are little jumper wires that are usually ate up by corrosion. When you get the board cleaned up you'll probably see the oxidized wire remnants.
 
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I acquired some of the spare parts (pic) I have ordered and so I started taking stuff apart and cleaning the board. I got the board cleaned (pic) after I removed some nearby parts. I really suggest everyone to get rid of that glue because it does horrible things to your precious electronics (pic).

I'll be posting more pictures and stuff as I go along with the project :)
 
Hello Lecroy

I will suggest you to replace the strange (burned ?:nono:eek:verheated ?:thumbsdn:) resistor between D114 and the red zener diode his value look like 3,9K ! :yes:
There is also another one (burned this one ) between the both transistors under the big whitewire on the right of your picture ...(may be this picture has been taken before you start to work ....?
 
I acquired some of the spare parts (pic) I have ordered and so I started taking stuff apart and cleaning the board. I got the board cleaned (pic) after I removed some nearby parts. I really suggest everyone to get rid of that glue because it does horrible things to your precious electronics (pic).

I'll be posting more pictures and stuff as I go along with the project :)

Second photo-right side--resistor standing upright between the two TO-126 transistors - to the right of the large caps mounting position...is toast..
 
I had an exciting moment today as I plugged in the amp to try it after replacing all parts marked red in this picture. After pushing the power switch it was very much less exciting. Power led and protection led lit, no smoke or anything like that. Protection won't go away so there's something wrong still.

Any idea how to start troubleshooting? As I said all the parts marked in picture above are changed as well as TR119, TR125, TR138 and TR134 at heatsink because TR119 and TR138 measured very low forward voltages using DMM. I replaced them with parts avionic suggested earlier in this topic.

Now I'm a bit out of ideas because I replaced all the parts that looked toasted and many parts that didn't look bad but where at the same "area" with toasted ones. Any ideas? :sigh:

--- EDIT ---
In addition to that picture I did also replace all the standard diodes on the left side of board picture, even though they are not marked in red. So diodes D122, D104, D106 and respective ones on other channel have also been replaced.
--- EDIT 2 ---
It seems that resistor R226 (3.9 kohm, 2 W) gets really warm very quickly then power is on. Also I measured something like 30 Vp-p sine wave on it's leg while power is on. I have a feeling that this isn't correct? Where should I try to find the problem?
 
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OK.If your sure all parts were installed correctly.And inspected for solder bridges on your solder connections.Then you need to start at the beginning and verify that all your power supply voltages are present and getting to the correct locations.
 
Any idea how to start troubleshooting?
You powered it up and no smoke..Thats good. Now you have to determine if ..

A. Any DC voltage is present at the amplifiers outputs.... or
B. Protect circuit has the correct power supply voltage....or
C. A malfunction in the protect circuit exists.

Once you get the protect circuit issue resolved .You still may not be out of the water.
There may still may be damaged components in the amplifier circuit.

When these M-80/M-85 amplifiers go south.Theres a lot of collateral damage.
 
You powered it up and no smoke..Thats good. Now you have to determine if ..

A. Any DC voltage is present at the amplifiers outputs.... or
B. Protect circuit has the correct power supply voltage....or
C. A malfunction in the protect circuit exists.

Once you get the protect circuit issue resolved .You still may not be out of the water.
There may still may be damaged components in the amplifier circuit.

When these M-80/M-85 amplifiers go south.Theres a lot of collateral damage.

I think that R226 (3.9 kohm, 2 W) resistor would actually start smoking if I kept power on long enough because it gets very very hot in matter of seconds after powering up.

I measured voltage between R and E wires and L and E wires that go to speaker connector board. If I understand correctly these are the outputs from the amp (relays seem to exist after these wires on the speaker connector board). Bad news: There's actually about -84 V between R-E and L-E (quite exactly the same value on both), no wonder the amp doesn't go out of protection :sigh:

Any ideas what could cause that kind of overly high DC offset? That -84 V seems to be the whole operating voltage of the amplifier am I right?
I quickly measured the rectifier bridges with DMM on the power board (same that has the big capacitors) and they seem to be fine (about 0.5 V forward voltage between every "diode").
 
I think that R226 (3.9 kohm, 2 W) resistor would actually start smoking if I kept power on long enough because it gets very very hot in matter of seconds after powering up.

I measured voltage between R and E wires and L and E wires that go to speaker connector board. If I understand correctly these are the outputs from the amp (relays seem to exist after these wires on the speaker connector board). Bad news: There's actually about -84 V between R-E and L-E (quite exactly the same value on both), no wonder the amp doesn't go out of protection :sigh:

Any ideas what could cause that kind of overly high DC offset? That -84 V seems to be the whole operating voltage of the amplifier am I right?
I quickly measured the rectifier bridges with DMM on the power board (same that has the big capacitors) and they seem to be fine (about 0.5 V forward voltage between every "diode").

You have another shorted output of driver transistor or a pre-driver transistor(s) is/are holding the output(s) at rail voltage. Verify that you have installed all those transistors correctly in the correct locations. Check your solder work for possible solder bridges between solder pads.
 
You have another shorted output of driver transistor or a pre-driver transistor(s) is/are holding the output(s) at rail voltage. Verify that you have installed all those transistors correctly in the correct locations. Check your solder work for possible solder bridges between solder pads.

The transistors I installed are installed correctly and I checked for solder bridges and found none. So I think there's shorted transistor(s) somewhere still. I previously measured rail voltage on both channel outputs, does that mean that I still have at least two shorted transistors (one on both channel)? Because I initally thought that only right channel was toasted because there was no visibly damaged parts on left channel (on right channel there certainly was). To be sure I did change all C3416 and A1352 transistors on left channel also when I changed the ones for right channel (the ones that stand free on main board).

Should I once again desolder all the transistors on the heatsinks and measure them again? What other transistors could be shorted than the ones on heatsinks and the C3416 and A1352 ones on main board? Do you think there's a toasted transistor on both channels still (because of outputs having rail voltage) or could a toasted transistor on one channel cause both channels to have rail voltage?
 
Are you saying your measuring LB or HB at both the Left and Right amplifiers output..?
 
Are you saying your measuring LB or HB at both the Left and Right amplifiers output..?

I measured the voltage on the speaker terminal board between the wires L and E (left channel?) and R and E (right channel?). If I understand correctly those are the output lines before relays (as the relays are on the speaker terminal board if I have understood correctly). So the voltage between L-E was about -84 V and between R-E also about -84 V (could the negative voltage point me somewhere? I connected the DMM so that positive wire went to L/R and negative to E). My copy of the service manual is quite bad, but if I guess +HB is about +88 V and -HB about -88 V, so that's quite close to what I get from the outputs? Do you know any place to get a better copy of the service manual?
 
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