Denon DRA-565RD Input Selector Issue: LC7821 System, 2SD2004 Transistor, R251 & R255 Resistors

Hello!

I am trying to fix a broken selector in my Denon (I will add that I am repairing this equipment for the first time in my life so please bear with me). The LC7821 system is responsible for this, which I already mentioned, unfortunately, does not switch inputs. I examined the supply voltage. They should be symmetrical +/- 15V and is -15V and + 6.5V. From the diagram I came across that the value of this voltage corresponds to the transistor 2SD2004.
And now my question is: resistors R251 and R255 are damaged. Should their exchange be enough or look for a reason?

 

Below I attach the service manual

I'm trying to understand why you started the topic and I'm fine.
Since you measured the resistor (after desoldering one end) and it is damaged (break or change in value?) Then why did not you replace it with a functional one, to see if the positive voltage is already right, but you ask us about it?
Bring the power system to proper operation, you will find out if the selector is already working or not.

I ask because it is late and I do not have access to these elements and I have a bit of an electronic store (50km and fuel costs). I will do shopping tomorrow and I want to know what I need to buy?

Measure the Zener diode and transistors TR251 and TR253. I asked - resistors in how they were damaged - a break or change in value (to which).

Stupid question

krakarak wrote:

Measure Zener diode and transistors TR251 and TR253.

how?

krakarak wrote:

I asked - resistors in how they were damaged - break or change of value (to which)

change in R251, should be 3.6k a is 460, R255 8.2k is 520.

_papa_ wrote:

Stupid question

krakarak wrote:

Measure Zener diode and transistors TR251 and TR253.

how?

If I'm too stupid to help you, just think for yourself.

krakarak wrote:

_papa_ wrote:

Stupid question

krakarak wrote:

Measure the Zener diode and transistors TR251 and TR253.

how?

Since I'm too stupid to help you, go on alone.

No! You did not understand me. I really do not know how to measure these transistors and diodes !?
Forgive me if I offended you.

An ohmmeter after desoldering from the system.

The meter is set to "diode measurement".
And these resistors have to measure again, earlier desoldering them on one side and then measure. It is very rare that it is the resistors fault, rather the Zener diode or the transistor mentioned above.
Buddy, do you think about repairing an amplifier, you already exchange integrated circuits (without previous voltage measurements) and you do not know how to properly measure semiconductor devices? After all, it's almost right after Ohma, BASIC knowledge of a technician. The meter is your additional senses. You do not have a single element lying loose and you never thought of measuring it to confirm what you are writing on electronic websites?
I am not writing to offend you, I know that everyone in various ways begins their adventure with electronics and devices, but without an assimilated theory supported by practice, you will not achieve anything. You need to know the principle of operation of each electronic element and the way of its measurement.
Without this knowledge and practice, you lie down and take your feet in the air ...

krakarak wrote:

Buddy, you are repairing an amplifier, you already exchange integrated circuits (without previous voltage measurements) and you do not know how to properly measure semiconductor devices?

The meter I have resistors I know how to measure, but I never had the opportunity to test transistors, I just did not know how it was done. I exchanged Lc7821 because I read such information on the internet. On the old LC switch, the voltages were good, and after changing the chip, "something went on."
I think this is a forum to learn from others.
Today I will replace this transistor 2SD2004 and resistors and see what will happen.

_papa_ wrote:

... I have resistors, I know how to measure ...

I asked and advised several times, maybe I will finally get the answer to the question - did you remove the resistors and sold off one end?
If not, then the measurement is wrong, adulterated by other elements. Can you set the meter (what you have this meter, name, model) for diode measurement, soldering iron, solder one end of Zener diode, pick it up and measure it. Then replace the ends of the meter and measure again. What are the readings?

krakarak wrote:

I asked and advised several times, maybe I will finally get the answer to the question - did you remove the resistors and sold off one end?

I checked without desoldering. Now I'm at work, if I come back, I will repeat the measurements.

First, desolder and check (descriptions of measurements of the transistor or diodes are on the Internet) Zener diode and transistors TR251 and TR253.

I checked the mentioned transistors and the zener diode. The transistors are probably for exchange, I'm not sure about the zener diode, but I'm sure to mention it.
What replacements of the above elements could I use?

TR251 = 2SD2004 transistor TO-92 npn 160V, 1.5A, 0.9W, replacement 2SD1812
TR253 = 2SC1740S transistor TO-92 (npn) 50V, 0.15A, note: http://www.secosgmbh.com/datasheet/products/SSMPTransistor/TO-92S/2SC1740S.pdf

Both you buy in the shop: http://north.pl/karta/2sd1812-tranzystor-to-92---npn--160v--15a--80mhz,631-AA-0056.html

Where else, look for it.

You did not check and you criticize. They are not "fancy replacements" but cheap and cheap transistors.
As for your proposal to insert a Uce = 30V transistor there, do not be surprised how it breaks through.
But advise, I'm already finishing in this topic.

Transistors are available with no problem and acceptable prices. I can not find the zener diode MTZJ6.2A anywhere. What equivalent could I apply?