Mackie CR4 amplifier no sound

[petehall347]

Re: Mackie CR4 amplifier no sound

how about R91 5.6k ?

[UserXP]

Re: Mackie CR4 amplifier no sound

https://www.badcaps.net/forum/showpo...4&postcount=30
Z1 3.9v . if shorted the base on q2 will be zero volts thus off .
R91 might be high

I tested all the diodes on the board.
D1 and Z2 read 0.6V forward foltage. When revesed, they read around 2.3V.
Z1 reads 0.6V forward voltage and around 1.2V backwards.

R92 reads 15kΩ, and the two resistors with a zig-zag around those Qs read 4.7kΩ, which is all in accordance with the schematics.

Also I noticed this: D1 diode (the one the is in parallel with the R77 resistor) shows continuity bothways, but I need to alternate the probles for that. If I put the probes in the red and black fashion on the diode contacts, I can hear a half s second continuity beep and then it stops. When I alternate the probles (black and red), the beep happens again in the same duration. Every successive probe alternation makes that short beep noise on the multimeter. I don't know, maybe it's picking the continuity from the surrounding components or caps.

The Z1 and Z2 diodes do not produce the beep on the continutiy check, yet they produce the readings I typed above. If one of them were shorted, I guess I would have heard a continuous beep.

[UserXP]

Re: Mackie CR4 amplifier no sound

budm, I was looking at this datasheet:


The CR schematics of that area says those two transistors are 2N5551. The datasheet I looked into shows different pad layout in terms of B, C and E for 2N5551 moar-mounted version (unless they made a mistake in labelling the contacts). That's why I "drew" the layout in one of my previous posts like this:

E---B
...C...

Left Leg --- Right Leg
.......Lower Leg........

The bias also confirm this. It is a NPN transistor, so when I put the positive probe on the B pad designated by the datasheet, I can measure the forward voltage on E and C with the negative probe. Did I use the wrong document or did I do something wrong?

[budm]

Re: Mackie CR4 amplifier no sound

Guys, I reattached my working CR4 PCB and measured the same spots. Everything is almost identical, except for the Pin 5 voltage. On my working CR4 it reads +13.08V in play mode and +19.90V in Mute mode, just as it is supposd to.

The voltages on Q1 and Q2 are "almost" the same (the orientation is as their contacts appear on the image above):

Q1:
Left leg: 000.0v Right leg:-1.9v
Base: +2.9v

Q2
Left leg: 000.5 Right leg: +2.9v
Base: +13.8v

Voltage reading of working unit per your reports:
The R88 also shows this (position from picture above):
Upper leg: (+12v)
|S|
|S|
Lower leg: (+2.9v)

Left leg = Emitter
Right leg = Base
Middle leg = Collector
So Q1 has correct reading.
Q2 is on so the Collector is at 13.8V but the E-B junction Voltage is not right at all, Emitter is 0.50V Base is 2.9V that means the E-B junction Voltage is 2.9V - 0.50V = 2.4V!
2N5551 spec: Vb-e sat is 1V, you have 2.4V.
https://cdn.badcaps-static.com/pdfs/...f419abb28e.pdf

[UserXP]

Re: Mackie CR4 amplifier no sound

Read my post #39 again.
Well, I do not see the test Voltage of R88, the resistance test of R81, the testing of Z1.
BTW, Are you saying that Q1 ans Q2 Voltage readings are the same as the non-working unit?
No way Q1 and Q2 readings of the working unit be the same as the non-working unit. Q2 has to be on, period, for you to get the sound.

Nope, some are very different (see previous post).

Sure thing, no problem. I will have to do that tomorrow, though. Thanks, budm.

[petehall347]

Re: Mackie CR4 amplifier no sound

How can I test that in circuit and what to replace it with if its faulty? It could be a zener diode, but I can't see the markings on the body and the specs just says Z1 3.9V.

just make sure its not shorted .

[UserXP]

Re: Mackie CR4 amplifier no sound

Well, in my post 37 I put the values on the picture of the non working unit.
In post 38 I posted values of the working unit in a similar orientation. Some of them are very different.

[UserXP]

Re: Mackie CR4 amplifier no sound

https://www.badcaps.net/forum/showpo...4&postcount=30

How can I test that in circuit and what to replace it with if its faulty? It could be a zener diode, but I can't see the markings on the body and the specs just says Z1 3.9V.

[budm]

Re: Mackie CR4 amplifier no sound

Read my post #39 again.
Well, I do not see the test Voltage of R88, the resistance test of R81, the testing of Z1.
BTW, Are you saying that Q1 ans Q2 Voltage readings are the same as the non-working unit?
No way Q1 and Q2 readings of the working unit be the same as the non-working unit. Q2 has to be on, period, for you to get the sound.

[petehall347]

Re: Mackie CR4 amplifier no sound

https://www.badcaps.net/forum/showpo...4&postcount=30
Z1 3.9v . if shorted the base on q2 will be zero volts thus off .
R91 might be high

[UserXP]

Re: Mackie CR4 amplifier no sound

Well, those other readings were the voltage readings when the unit was On I had taken before and into image. Is there another possible component that could make the Qs not to work right?
On the far right, there is a diode symbol. It says it is Z1, but there is no marking for it in the service specs. It is connected to the Q1 and R88. Could this be a miniature 12V restriction circuit (like the one with Z3 and Z4 zener diode and the two big resistors R1 and R2 that usually scorch the board) needed to provide the 12V for the TDA to be in play mode? Maybe there is something wrong there which makes the wrong voltages you have noticed?
I am just making a wild guess here.

[budm]

Re: Mackie CR4 amplifier no sound

OK, here's what I got. I found that this type of transistor is 2N5551 NPN type. So the base pin is the P end. I placed the positive probe on the P tab, and the negative on the E and C tabs.
The data sheet says the layout is as follows:

E---B
C

I set the multimeter on diode setting and tested Q1 and Q2. Both show +0.700 value, with the emitter tab having 0.004 higher value than C, and both transistors read almost the same.

So the E-B junction is basically the same for Q1 and Q2 but I do not understand the other readings.

[UserXP]

Re: Mackie CR4 amplifier no sound

OK, here's what I got. I found that this type of transistor is 2N5551 NPN type. So the base pin is the P end. I placed the positive probe on the P tab, and the negative on the E and C tabs.
The data sheet says the layout is as follows:

E---B
C

I set the multimeter on diode setting and tested Q1 and Q2. Both show +0.700 value, with the emitter tab having 0.004 higher value than C, and both transistors read almost the same.

[budm]

Re: Mackie CR4 amplifier no sound

OK, sorry for me not knowing. I meant whether it should be removed from the pcb?

Try it without removing first, you also have working unit to compare the result, if it reads not correct then remove and retest.
Do not do component testing when the unit is powered, the only time you do the test when the unit is powered is when you do the Voltage testing.

[UserXP]

Re: Mackie CR4 amplifier no sound

OK, sorry for me not knowing. I meant whether it should be removed from the pcb?

[budm]

Re: Mackie CR4 amplifier no sound

Q1 and Q2 are the same so all you need to do is to search the web on how to test NPN Transistor, you also have working board for comparison.
You also need to to test the Voltages and other parts as I listed in my post #39.

[UserXP]

Re: Mackie CR4 amplifier no sound

Thanks, budm.
Yes, I measured it three times. The difference is +/-000.2 or so between the different measurments.
That's why i checked, I think on the working PCB the readings are different.
How should I test this Q2? You think it's bad? If it is, why did it work shortly today and died again, I mean, if the Q2 component is faulty, can it work intermitently like that?

What should I test with these components? Voltages when the unit is on?

[budm]

Re: Mackie CR4 amplifier no sound

https://www.badcaps.net/forum/attach...1&d=1603549453

Are you 100% sure that Q2 Base is 1.1V and the Emitter is at 0V?
If Base is 1.1V that means Q2 E-B junction is bad, it should be about 0.6 ~ 0.7V when it is forward bias for it to be on, right now Q2 is not turned on that is why the Collector Voltage is at 19V, Q2 has to be on for Play mode.
You need to test that Q2, R91 (5K6 Ohms), Diode Z1.
Also test R88 Voltages.

[UserXP]

Re: Mackie CR4 amplifier no sound

Guys, I reattached my working CR4 PCB and measured the same spots. Everything is almost identical, except for the Pin 5 voltage. On my working CR4 it reads +13.08V in play mode and +19.90V in Mute mode, just as it is supposd to.

The voltages on Q1 and Q2 are "almost" the same (the orientation is as their contacts appear on the image above):

Q1:
Left leg: 000.0v Right leg:-1.9v
Base: +2.9v

Q2
Left leg: 000.5 Right leg: +2.9v
Base: +13.8v

The R88 also shows this (position from picture above):
Upper leg: (+12v)
|S|
|S|
Lower leg: (+2.9v)

[UserXP]

Re: Mackie CR4 amplifier no sound

Here are some more measurements. I don't know if these are the right voltages. Pin 5 should receive ~12V in order to unmute, yet it receives the full +19V voltage and is stuck in the Mute mode. Occasionaly, a very faint crack can be heard here and there when I put my ear very close to the speakers while they are in that stuck mute mode.

The lead that connects the circuit (JP) is desoldered, as you can see in the image. Upon making contact, the amplifier mutes. As soon as contact is removed, the amplifier kicks in and plays the sound superbly, no hissing, crackling or other artifacts.
This malfunction is so annoying!