How do I test these transistors? (electronics noob here)

[Skyhooker]

Hi, everyone,

First post here. I was recently given what would be a very nice Sony receiver, a STR-V555ES, if it didn't go into Protect mode. I'm very new to electronics circuitry, though I have a digital multimeter and am a fair hand at soldering (I've replaced a number of PC components, including blown caps). From what I've gathered so far, these errors are often caused by failure of the output transistors, so I figured I'd begin by testing those. This model, however, doesn't have the usual 3-lead transistor and separate emitter resistor, but instead has the emitter resistor built into it in a 5-lead configuration.

My question is how to test them? I will link the datasheet here, but they are Sanken SAP15, in case you are familiar with them.

Any other recommendations on how to troubleshoot this receiver also appreciated. It doesn't always go into Protect mode right away - in fact when I was first given it, I ran it for several hours with no errors, and it only went into Protect the next time I started it. It doesn't seem to matter whether any speakers are connected or not.

Thanks!

 

[HellasTechn]

This is IGBT i think. Correct me if im wrong but you can test them like a normal transistors (darlington pair) using B,C,E pins and B-D pins to test the base diode.

 

[PETERDECO]

Do they get hot before the protection circuit activates?

 

[bertus]

Hello,

@HellasTechn , They are NOT IGBT's as there is no mosfet as first transistor.
They are special darlingtons with extra resistors and diodes build in:



You can at least measure the resistors between S and E, they should be about 0.22 Ohms.
Also you can measure de diode(s) between B and D.
The PNP version has even 4 diodes, so you will need likely a higher voltage to see them.
You can also check the B , C from both transistor.
Between the other pins will be difficult due to the interal resistor on B , E of the second transistor.

Bertus

 

[Skyhooker]

Hello,

@HellasTechn , They are NOT IGBT's as there is no mosfet as first transistor.
They are special darlingtons with extra resistors and diodes build in:

View attachment 49693

You can at least measure the resistors between S and E, they should be about 0.22 Ohms.
Also you can measure de diode(s) between B and D.
The PNP version has even 4 diodes, so you will need likely a higher voltage to see them.
You can also check the B , C from both transistor.
Between the other pins will be difficult due to the interal resistor on B , E of the second transistor.

Bertus

Great, thank you, I will try those tests. As I mentioned, I have very little experience with anything but the most rudimentary of electronic repairs, like replacing blown capacitors on PC motherboards, but my understanding is that stereo output transistors come in pairs of NPN and PNP, so I will try to test them accordingly.

 

[Skyhooker]

Do they get hot before the protection circuit activates?

Not that I can tell, no. Usually the Protect kicks in instantly when the relay closes (I assume it's a relay, and it works the same way in my other Sony receiver) a few seconds after hitting the power button. Also, I always reduce volume to zero before turning on a receiver.

 

[Harald Kapp]

the Protect kicks in instantly when the relay closes

In that case it is very likely not a thermal protection, but a DC protection circuit. DC components in the output of an amplifier can damage the speakers so it is well to turn the amplifier off if a DC components is present. Do you have a service manual? Check the voltages as indicated (if there are any) to see where the DC component may come from.

 

[Skyhooker]

Do you have a service manual? Check the voltages as indicated (if there are any) to see where the DC component may come from.

I did manage to find the service manual (I'll upload if able), but I'm not much for reading schematics yet. I don't see any listing of voltages to test, apart from some resistors that can be adjusted on the power amp board. If anyone has the time and inclination and can see any particular components I should test, please let me know - thanks!

P.S. Service manual too large to upload - I'll try to find the link.

P.P.S. This link looks clean - pretty sure it was the one I used to get the PDF: STR-V555ES Service Manual

 

[Harald Kapp]

Have a look at this section on page 32 (and the other equal ones for the other channels):

The numbers I circled are voltages. Look especially for the 0 V points. If DC is present, these voltages will be <> 0 V.

 

[Skyhooker]

I see, will check those out - thanks!

 

[Skyhooker]

Have a look at this section on page 32 (and the other equal ones for the other channels):
View attachment 49707
The numbers I circled are voltages. Look especially for the 0 V points. If DC is present, these voltages will be <> 0 V.

The interesting part as an absolute beginner at this is going from the schematic circuit diagram and translating it to the actual component positions on the board diagram - let's just say I'm finding it a challenge.

Also, just to make sure so I don't damage something (or myself), when testing live voltages, do I connect the negative multimeter lead to chassis ground, like the back panel, while measuring at the component with the positive lead? Thanks again.

 

[Ylli]

A common failure of output transistors is a collector-emitter short. That is also a measurement you can make on these. DMM on diode test range should show open in both directions between C and S pins.

 

[Harald Kapp]

do I connect the negative multimeter lead to chassis ground

Try it. Chassis ground is not necessarily common ground of the circuit. IF your voltage measurements all are way off, then you'll have to find the "real" ground these voltages are referenced to.
The symbol in the schematic is this: