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Old 10-24-2020, 02:08 PM   #41
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Default 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.
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Last edited by budm; 10-24-2020 at 02:09 PM..
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Old 10-24-2020, 02:10 PM   #42
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Default Re: Mackie CR4 amplifier no sound

OK, sorry for me not knowing. I meant whether it should be removed from the pcb?
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Old 10-24-2020, 02:28 PM   #43
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Default Re: Mackie CR4 amplifier no sound

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Originally Posted by UserXP View Post
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.
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Old 10-24-2020, 03:30 PM   #44
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Default 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.

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Old 10-24-2020, 03:48 PM   #45
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Default Re: Mackie CR4 amplifier no sound

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Originally Posted by UserXP View Post
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.
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Old 10-24-2020, 03:58 PM   #46
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Talking 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.

Last edited by UserXP; 10-24-2020 at 04:00 PM..
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Old 10-24-2020, 04:11 PM   #47
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Default 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

Last edited by petehall347; 10-24-2020 at 04:17 PM..
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Old 10-24-2020, 04:12 PM   #48
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Default 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.
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Old 10-24-2020, 04:20 PM   #49
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Default Re: Mackie CR4 amplifier no sound

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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.
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Old 10-24-2020, 04:24 PM   #50
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Default 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.
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Old 10-24-2020, 04:26 PM   #51
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Default Re: Mackie CR4 amplifier no sound

Quote:
Originally Posted by UserXP View Post
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 .
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Old 10-24-2020, 04:27 PM   #52
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Default Re: Mackie CR4 amplifier no sound

Quote:
Originally Posted by budm View Post
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.
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Old 10-24-2020, 04:38 PM   #53
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Default Re: Mackie CR4 amplifier no sound

Quote:
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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://www.onsemi.com/pub/Collateral/2N5550-D.PDF
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Old 10-25-2020, 04:09 AM   #54
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Default Re: Mackie CR4 amplifier no sound

budm, I was looking at this datasheet:
https://www.onsemi.com/pub/Collateral/2N5551-D.PDF

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?

Last edited by UserXP; 10-25-2020 at 04:52 AM..
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Old 10-25-2020, 04:49 AM   #55
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Default Re: Mackie CR4 amplifier no sound

Quote:
Originally Posted by petehall347 View Post
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.
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Old 10-25-2020, 05:30 AM   #56
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Default Re: Mackie CR4 amplifier no sound

how about R91 5.6k ?
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Old 10-25-2020, 06:42 AM   #57
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Default Re: Mackie CR4 amplifier no sound

Quote:
Originally Posted by petehall347 View Post
how about R91 5.6k ?
Yes, it reads 5.66kohm. The one above (R22) reads 9.9-10kohm.

Last edited by UserXP; 10-25-2020 at 06:55 AM..
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Old 10-25-2020, 07:39 AM   #58
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Default Re: Mackie CR4 amplifier no sound

Q2 is the prime suspect .
i suppose you could try a jumper between C and E of Q2 and see if it plays sound then .

Last edited by petehall347; 10-25-2020 at 07:42 AM..
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Old 10-25-2020, 11:39 AM   #59
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Default Re: Mackie CR4 amplifier no sound

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Q2 is the prime suspect .
i suppose you could try a jumper between C and E of Q2 and see if it plays sound then .
Would that safe to do? I mean, I wouldn't want to damage anything else in the circuit.
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Old 10-25-2020, 12:34 PM   #60
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Default Re: Mackie CR4 amplifier no sound

it should be ok so long as you dont short anything else and you short the correct points .
you could wait to see what budm says in case i am missing something
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