Mackie CR4 amplifier no sound

[petehall347]

Re: Mackie CR4 amplifier no sound

you said no volts across R22 i would expect there should be .

[UserXP]

Re: Mackie CR4 amplifier no sound

put it back and try the new transistor ..be sure of transistor pin out

I barely managed to put this R22 back because it was very unapproachable to access its holes and keep the resistor in place for sodering. It fell out too many times.
I will attempt to desolder Q2 without damaging it, but it is so tiny i am afraid the soldering iron is going to melt it. If it turns out Q2 is not faulty, I will have no replacement. My local stores do not have the SMD type of these amplifier transistors in stock.

[UserXP]

Re: Mackie CR4 amplifier no sound

I see that one contact of this R22 is connected to Z2 coming from the positive rail. The other is in contact with the ground through a joint near Q1.
On the working unit, when probes are placed on this resistor, it reads 9.9~10kOhm.

[petehall347]

Re: Mackie CR4 amplifier no sound

put it back and try the new transistor ..be sure of transistor pin out

[UserXP]

Re: Mackie CR4 amplifier no sound

will be c39 charging up .. swap meter leads

Swapped, no reading now. It stays at ".OL" on display.

[petehall347]

Re: Mackie CR4 amplifier no sound

try swapping meter leads

[UserXP]

Re: Mackie CR4 amplifier no sound

now measure the board where the resistor came from

The same, it starts from 4.2kOhm and then slowly increases to 5, 6, 7...

[petehall347]

Re: Mackie CR4 amplifier no sound

now measure the board where the resistor came from

[UserXP]

Re: Mackie CR4 amplifier no sound

Unsoldered R22 from the PCB and measured, now it reads 9.9~10kOhm.

[UserXP]

Re: Mackie CR4 amplifier no sound

R22 is the first of the two resistor above Q2:

-R22-
-R91-
-Q2-

On the other unit it reads 10kOhm like it's supposed to be.

[UserXP]

Re: Mackie CR4 amplifier no sound

Hello, people.
Sorry for this delay, hopefully you are all OK and safe.

OK, here's the update: Today I bought four 2N5551 transistors for testing purposes, but I couldn't find the SMD version, so I though these would do for testing as budm suggested. Now, he suggested an open pathway between Q2 and the ground... I did some more testing...

Now, I did some more measurements prior to deciding to unsolder the SMD Q2. I again tested its forward voltages and they are the same like in the previous measurements, around 0.600 and seemes OK. However, I decided to check the components again. Now, here is some interested news... I tested all the through-hole resistors in this area and refered to the schematics. The unit was off during these measurements:

R87=4.7kOhm
R88=4.7kOhm
R91=5.6kOhm

Now, R22 is strange and I think it didn't behave like this before. Sometimes the multimeter displays 00.00kOhm, other times it starts at 4.2kOhm and will not stop, it continues to show the increasing number of kOhms. If I move the probes and touch again, it continues to count where it left off, as if something is "charging" the resistance. I also got a positive continuity result when touched this specific resistor with the probes a couple of times, but not always. This happens only with R22.

When I turn on the unit, the voltage across that resistor is 000.0mV and the resistance test shows 0. According to the specs, R22 should be around 10kOhms. Can a resistor become faulty and work intermitently, or are these readings due to in-circuit measurements.
Does this tell us anything, is it normal?

[UserXP]

Re: Mackie CR4 amplifier no sound

any updates ?

Sorry, I had a crazy week. Due to a sudden increase in the number of new corona cases in my country, there have been changes and new measures at my work being put into effect, so the whole week was in rescheduling and re-organizing activities and work from home, so I didn't have much free time.
I will post back in a couple of days for sure. Thank you so much for helping me with this and for having the patience.

[petehall347]

Re: Mackie CR4 amplifier no sound

any updates ?

[budm]

Re: Mackie CR4 amplifier no sound

You can use the through hole Transistor so it will be easy to solder for testing, the 2N2222 or 2N3904 are very generic Transistors so should be easy to get, just remember that pin out of the through hole is not the same as the SMD.

[UserXP]

Re: Mackie CR4 amplifier no sound

Do you have any small through hole 3-leg NPN Transistor such as 2N2222, 2N3904 around?

I doubt that, but there is an electronics store relatively near by my place, I can go purchase one tomorrow (it's almost midnght here now ). Should I go for the ones you listed above or buy the 2N5551 one?

[budm]

Re: Mackie CR4 amplifier no sound

Do you have any small through hole 3-leg NPN Transistor such as 2N2222, 2N3904 around?

[UserXP]

Re: Mackie CR4 amplifier no sound

The service guy sent me these pieces of the schematics, but i asked if it would be OK to provide full specs since this product is no longer produced. I am waiting for a reply. Maybe we'll finally get the CR4 schematics. Too bad I won't know how to interpret them, though.

[UserXP]

Re: Mackie CR4 amplifier no sound

OK.
Make sure to unplug the AC from the unit when making diode test, resistance test just in case the power switch is not hard switch.

OK, not a problem, I always unplug the unit from the mains socket when in off state.

[budm]

Re: Mackie CR4 amplifier no sound

OK.
Make sure to unplug the AC from the unit when making diode test, resistance test just in case the power switch is not hard switch.

[UserXP]

Re: Mackie CR4 amplifier no sound

Sorry, I spotted the error and while I was editing my post you replied.