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Sony N77ES blown a fuse

Also just FYI, the transistor will check like a diode between the base and emitter in one direction only. Both directions shows its shorted.
 
Sorry, gotta drop out for a few hours! Others here are also pretty knowledgeable with these if they also want to chime in.
 
Thank you again and please keep coming with ideas.

Regarding the reading on both directions on the other transistors,I believe it is happening due to the measuring being done with them on the board, as they have consistent readings between themselves. Does this make sense?

I am ordering a 2SC3856 to try it, but locally I can't find a Sanken one like the originals, Should it be OK to try with one from another brand (probably unbranded chinese)?
 
Sad update... I installed the new 2SC3856 and the reading with it installed is the same with the original one-
I tested the old transistor out of the board and it read fine, so the transistor was not on short by itself.

I am getting desperate... can you please give some more ideas to try to find where the short/problem could be?
 
Remove completely a 2SC3856 from the good channel and compare its readings. I really wished you could have gone a little slower as if we were to determine that that was the problem, then you would have to check other components in its chain before doing any replacements or repair.

It is hard for me to armchair diagnose anything from a distance. What state do you live in?

Post some pics as asked please.

I am sending you a private message via "conversations".
 
I live in Portugal, very far from the States:... )

I will try to take the pictures tonight but if they are not good, I will try to take better pictures in the morning.

Thank you :)
 
I removed all the output transistors 2SC3856 and 2SA1492 and tested them, they all seem well, no shorts.


Karl vd Berg said:
Usually the first two should go higher in resistance. You can measure them with one lead out of circuit and take notes on paper. Same for the smaller 47Ω ones. Please, report back.
Click to expand...

I removed one leg of the board for the R452 - 100Ω. - and now it reads 106,0 Ω, so it should be fine.

I have not removed the Power transistors (?) 2SC3298A and 2SCA1306A. Should I test them or should I go on another direction?


IMG_2010.jpg


So I really need guidance to the next step.
I am very stressed having my N77ES not working.
 
As I was with the solder iron I went further and removed these transistors too. One pair (right on the photo) of the 2SC3298A and 2SCA1306A are dead - reads 0.0000 on both directions on both transistors. The other pair reads fine.

Could this be guilty guys?

As I will need to solder all the others again, should I replace all them with new ones? Or should I keep the output transistors as they seem all well?
 
If the output transistors are fine, you keep them. Only the 2SC3298A and 2SCA1306A dead TO-220F pair has to go. Toshiba used to have the 2SA1930 and 2SC5171 pair (also TO-220F package) that would suit good, specially for current collector (Ic: 2A). At the moment, seems that only the MJF15030 and MJF15031 pair look suitable, though they are 150V (originals are 180V), and fT is 30MHz (originals are 100MHz). If you can't find originals or the Toshiba's above, try the 15030/15031.

R452 at 106Ω is not really fine and it tends to go higher. I'd replace it with this one. Applies to all the 100Ω / 0.5W fusistors you'll find in the amp.

R454 (10Ω) measuring 5.8Ω also needs to be replaced, with this one. Also applies to all the 10Ω / 0.5W fusistors in the amp.
 
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Thank you Karl.

After removing the dead 2SC3298A and 2SA1306A TO-220F the R454 (10Ω) measured 10.6Ω, so should be Ok (?).

I am having trouble finding the original and the first replacement pair you sugested (2SA1930 and 2SC517).

I did a search and found a pair of Sanken that are sugested in a couple of web sites as replacements to the originals and still in production by Sanken:
2SC3298A -> 2SC4883A (Sanken) 180V version
2SA1306A -> 2SA1859A (Sanken)180V version

http://www.semicon.sanken-ele.co.jp/sk_content/2sc4883_ds_en.pdf
http://www.semicon.sanken-ele.co.jp/sk_content/2sa1859_ds_en.pdf

I see some diference in the specs and I don't see a reference to Power transistors in the sheets, but could these ones be a good match and replacements for the originals?
 
CRM said:
2SC3298A -> 2SC4883A (Sanken) 180V version
2SA1306A -> 2SA1859A (Sanken)180V version

http://www.semicon.sanken-ele.co.jp/sk_content/2sc4883_ds_en.pdf
http://www.semicon.sanken-ele.co.jp/sk_content/2sa1859_ds_en.pdf

I see some diference in the specs and I don't see a reference to Power transistors in the sheets, but could these ones be a good match and replacements for the originals?
Click to expand...
These are excellent ones! I suggest you to buy a few and keep a few as spare parts, just in case.
 
Karl vd Berg said:
These are excellent ones! I suggest you to buy a few and keep a few as spare parts, just in case.
Click to expand...

Meanwhile I remembered that I have access to an amplifier that is not used from a long time (and I will not use it). Looking to the Service Manual it uses about 3 or 4 pairs of 2SC5171/2SA1930. I think I will open it and check them. If they are OK, I could try to install them in the N77ES.

What do you think? Should I give it a try?
 
It is an Onkyo receiver TX-DS979.

After about 100 screws and some mild destruction I was ablle to access the 2SC5171/2SA1930. Bad surprise... Onkyo did cut a part of the pins, so they are a little short to put on the Sony. There is way to work around but prior to that I went to check something else...

Going back to my board and O47, the transistor with 0.000 value but after all was fine, I decided to check the place where it would be connected and... opsss testing just the points where the extremes of the transistor would be connecting they should the value 0.000, the other places where the other transistor are to be resoldered does not show this value of short. So something else in the chain before the transistor is on short, I think.

What can that be?

Help again, please!
 
it helps if you can have a basic understanding of how amplifiers work .
basically the drivers are the transistors that drive the outputs . and right before the output transistors and in most cases right next to the outputs . looking at the circuit diagram helps .
 
q453 q454 q451 q452 are drivers .
and q403 q404 q401 q402 for other channel
there are 6 outputs per channel and cannot be tested in circuit reliably . same with drivers without removing lots of resistors .
 
for testing purposes you can remove all outputs for safe keeping if still good then get the rest squared away first then test with one pair of outputs .
 
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