OK, i have now connected J222,J223,J224,J225 togheter with J401. CN302A still disconnected.
I have also checked that i have connection on all.
Soldered the wires from my mini grabbers togheter.

So here are my new measurements:

LEFT CHANNEL:
R401: 0 Volt
R403: 0 Volt
R409: +0,5 Volt
D401: +0,5 Volt

R411: -0,5 Volt
D403: -0,5 Volt

R425: -62 Volt on leg nearest heat sink, +64 Volt on the other

R413: 0 Volt
R415: 0 Volt

D409: +8 Volt
D411: -8 Volt

RIGHT CHANNEL:
R402: 0 Volt
R404: 0 Volt
R410: +0,5 Volt
D402: +0,5 Volt

R412: 0 Volt
D404: -0,5 Volt

R426: -62 Volt on leg nearest heat sink, +62 on the other

R414: -55 Volt
R416: -55 Volt

D410: -55/-46 Volt
D412: -63/-55 Volt


(I guess 0,5 Volts are equal to zero in this measuring?) but just wrote it anyway because i wasn't totally sure.

 

Now we have to do some transistor testing with your DMM set to the diode test range.



We are going to test the transistors while out of circuit:

Q406 2SC2631
Q408 2SA1132

This is what Q406 (NPN) looks like. Q408 has the same pinout but it is PNP (the arrow on the emitter points inwards towards the base).

For each transistor,

Connect RED probe to B.
Record DMM reading with BLACK probe connected to E.
Record DMM reading with BLACK probe connected to C.

Reverse the measurements as follows:
Connect BLACK probe to B.
Record DMM reading with RED probe connected to E.
Record DMM reading with RED probe connected to C.

Connect RED probe to E.
Record DMM reading with BLACK probe connected to C.

Reverse the procedure as follows:
Connect BLACK probe to E.
Record DMM reading with RED probe connected to C.

Here is what we are looking for in the above transistor tests.
Each transistor appears as two diodes connected at the BASE.
Q406 is an NPN transistor. When the RED probe is connected to B, you should see a diode conducting with a voltage drop of about 730mV when the BLACK probe is connect to C and then to E. All other readings should read as open circuit.

Q408 is a PNP transistor with the same results except that the diode conducts when the BLACK probe is connected to B.

At this point, you will likely have to purchase more replacement transistors. I cannot predict ahead of time which transistors will need to be replaced. It would not be a bad idea to purchase a collection of the ones we are trouble-shooting at this stage, from Q401 to Q430 and Q501 to Q518.

 

Ok,thanks.
I will buy a collection of transistors, do you know exactly what types Q401 -> Q430 and Q501 -> Q518 are, then i can order just now, i'm not at the amp right now.

You wrote: "We are going to test the transistors while out of circuit"
With this, you mean i will have to take out each transistor for testing, right ?

 

Ok,thanks.
I will buy a collection of transistors, do you know exactly what types Q401 -> Q430 and Q501 -> Q518 are, then i can order just now, i'm not at the amp right now.

You wrote: "We are going to test the transistors while out of circuit"
With this, you mean i will have to take out each transistor for testing, right ?

No.
For now, we are only testing Q406 and Q408 because you have already unsoldered them and I suspect Q406 is bad.

Back in post #37 I pointed out that one approach to repair is to replace all the transistors and then hope for the best. This may or may not work and then what did you learn besides how to replace transistors.

My approach is to follow through the circuit and fix what needs fixing. At this stage, we are only testing a tiny part of the circuit, Q406 and Q408. Of course, this process is going to take longer especially if you have to wait for parts to arrive.

We are at a great advantage because

1. we have the circuit schematic
2. the normal operating voltages are well documented in the circuit schematic
3. we have two identical channels to compare.

The actual components used by Technics is listed in the parts listing and also on the circuit schematic. In the event that you cannot obtain exact replacements we will attempt to find the closest equivalents. In a best case scenario, only a few of the transistors might need to be replaced. The issue is finding the bad ones. In some cases, we will be able to find the bad transistors without having to remove them. We will test the transistors in circuit, identify the suspects, and then remove them and confirm that they are bad.

As we move along the test and repair, I will attempt to explain what I am doing along the way, assuming that you have some knowledge of electronics and can read and follow the circuit schematics.

 

Sorry, i just didn't realize i had taken out Q406 and Q408, i thought it were some transistors who stood on the PCB, that's why i asked to take them out to measure, since you wrote "out of circuit".
I was not referring to the "shotgun" method you mentioned earlier, just a little misunderstanding.
I also know the components are listed in the parts listing, but i thought it was genuine Technics part numbers, but i see it's not.

Soo, i did measure the transistors the way you told me to, i made a mistake and thought at first my readings where OHM..
(as you can see in my picture)

Anyways, here are measurements:

Q406:
Connect RED probe to B.
Record DMM reading with BLACK probe connected to E: 668 mV
Record DMM reading with BLACK probe connected to C. 258 mV
Reverse the measurements as follows:
Connect BLACK probe to B.
Record DMM reading with RED probe connected to E. 950 mV
Record DMM reading with RED probe connected to C. 262 mV
Connect RED probe to E.
Record DMM reading with BLACK probe connected to C. 900mV
Reverse the procedure as follows:
Connect BLACK probe to E.
Record DMM reading with RED probe connected to C 700mV

Q408:
Connect RED probe to B.
Record DMM reading with BLACK probe connected to E. Open circuit.
Record DMM reading with BLACK probe connected to C. Open circuit.
Reverse the measurements as follows:
Connect BLACK probe to B.
Record DMM reading with RED probe connected to E. 890 mV
Record DMM reading with RED probe connected to C. 862 mV
Connect RED probe to E.
Record DMM reading with BLACK probe connected to C. Open circuit.
Reverse the procedure as follows:
Connect BLACK probe to E.
Record DMM reading with RED probe connected to C. Open Circuit.


As i understand, you are right about Q406..

 

That confirms that Q406 is bad and needs replacing.
And that is why R414 keeps burning up.

I will look into the next line of attack but it may take another day for me to get around to it.
I am hoping that we can locate a few more bad transistors so that we will know what to order.

 

A bad transistor! I feel we're getting somewhere!
Thank you for guidance.

 

Until you replace Q406 with a new transistor and reinstall Q408, we will proceed with tests on the LEFT channel.

Everything looks good from Q401 to Q415.

With the hookups remaining as is,

Check the voltages at:

R427
R429
R433
R437
R443
R445
R459
R463

 

You are now a trained transistor checker!

While you have these transistors out, you can go ahead and test as you have done before.

Q424 is the same as Q406 2SC2631 NPN
Q426 is the same as Q408 2SA1123 PNP

Q428 NPN 2SC3944
Q430 PNP 2SA1535

are power transistors and the pinout is as shown below (except Q428 is NPN).

 

Yes i am a transistor checker

I will test the transistors tomorrow.

I have measured the voltages today on the resistors you told me to, measured both legs... i guess something's not right..

R427: +1,3 Volt / +7,6 Volt
R429: -1,2 Volt / -7,7 Volt
R433: -0,7 Volt / +1,3 Volt
R437: -1,2 Volt / -0,7 Volt
R443: +0,3 Volt / +0,02 Volt
R445: -0,3 Volt / -0,02 Volt
R459: +7,6 Volt / +6,6 Volt
R463: +6,8 Volt / +6,6 Volt

 

That's good news.
All the voltages match up with those in the schematics.
That suggests that that section is ok.

Now we move on to the power amplifier stage, Q501 to Q517

 

You might as well remove Q503 and test all six power transistors.
All power transistors below have the same pinout (BCE) as the power transistors Q428, Q430.

Q501 NPN 2SC1815 (same pinout as before ECB)

Q503 NPN 2SC3944 power
Q505 PNP 2SA1535 power

Q507 NPN 2SC3182 power
Q515 NPN 2SC3182 power
Q509 PNP 2SA1265 power
Q517 PNP 2SA1265 power

Go ahead and replace R509 and R513 if you have not already done so:
R509 680Ω ¼W
R513 330Ω ¼W

 

I have now removed Q503, and replaced R509 and R513.
Have not turned it on after this yet.

I have also checked all the transistors now, i can almost be sure which of them is bad and not, but since i'm such a fresh transistor checker i will post the readings for you to read anyway

Q424:
This one is cracked if you remember, it has open circuit in every measurement.

Q426:
Connect RED probe to B.
BLACK probe connected to E: 32 mV
BLACK probe connected to C: 29 mV
Reverse the measurements as follows:
Connect BLACK probe to B.
RED probe connected to E: 32 mV
RED probe connected to C: 29 mV
Connect RED probe to E.
Record DMM reading with BLACK probe connected to C: Short circuit.
Connect BLACK probe to E.
Record DMM reading with RED probe connected to C: Short Circuit.

Q428:
Connect RED probe to B.
BLACK probe connected to E: 23 mV
BLACK probe connected to C: 21 mV
Reverse the measurements as follows:
Connect BLACK probe to B.
RED probe connected to E: 23 mV
RED probe connected to C: 20 mV
Connect RED probe to E.
Record DMM reading with BLACK probe connected to C: Short circuit.
Connect BLACK probe to E.
Record DMM reading with RED probe connected to C: Short circuit.

Q430:
Connect BLACK probe to B.
RED probe connected to E: 766 mV
RED probe connected to C: 756 mV
Other readings are open circuit on this.

Q501:
Connect RED probe to B.
BLACK probe connected to E: 932 mV
BLACK probe connected to C: 939 mV
Other readings are open circuit on this.

Q503:
Connect RED probe to B.
BLACK probe connected to E: 784 mV
BLACK probe connected to C: 780 mV
Other readings are open circuit on this.

Q507:
Connect RED probe to B.
BLACK probe connected to E: 696 mV
BLACK probe connected to C: 691 mV
Other readings are open circuit on this. This is a new one, old one shooting flames, checked it anyway..

Q515:
Short circuit on every measurement.

Q505:
Connect BLACK probe to B.
RED probe connected to E: 770 mV
RED probe connected to C: 758 mV
Other readings are open circuit on this.

Q509:
Short circuit on every measurement.

Q517:
Connect BLACK probe to B.
RED probe connected to E: 628 mV
RED probe connected to C: 607 mV
Other readings are open circuit on this.



So after what i have learned so far, i guess we have some bad transistors here..
Q424, Q426, Q428, Q509 and Q515 are bad. Am i right?

 

Yes. You are doing well.
Now you know which transistors need replacing.

Do not solder the replacement transistors until I give the OK.

Let me know what transistors and quantity you already have in stock.
You can go ahead and order replacements that you do not already have, along with replacement resistors.
Don't forget to order replacement for Q420.
Having spares on hand would be a good idea.

 

Nice. I will not solder any transistor before ok.

I do have

5 of Q509
4 of Q515
2 of Q428

Missing replacements for

Q406
Q420
Q424
Q426

I have enough 0,25W resistors of 100 ohm, 330 ohm, 560 ohm and 680 ohm,

 

Good.

You can install
Q501
Q503
Q505
R513 330Ω

Turn ON power and measure voltages at
R513

If the voltages are close to +0.5V and -0.5V, turn OFF power, unplug and install
Q507
Q509 (a new one, of course)

Turn ON power and measure voltages, again at
R513
and
TP501

We're looking for voltages close to 0V in all cases,

and of course, no smoke or flames.

 

Marius83

If you want to stop burning and blowing components when first powered up, wire an incandescent light bulb in series before the amplifier.
If there is a short, or shorts, as is evident, then the bulb will light up and consume the power rather than your components. If no short, the bulb will not light up. Try 100 watt to begin with

 

Nice. I will not solder any transistor before ok.

I do have

5 of Q509
4 of Q515
2 of Q428

Missing replacements for

Q406
Q420
Q424
Q426

I have enough 0,25W resistors of 100 ohm, 330 ohm, 560 ohm and 680 ohm,

 

 

Known as a dim bulb tester