Mackie CR4 monitors

[petehall347]

Re: Mackie CR4 monitors

complete supply outside would be better than just the transformer alone
only problem might be is from extended wiring needed .

[R_J]

Re: Mackie CR4 monitors

You would need a center taped transformer. The transformer output is 14vac - Common - 14vac

[UserXP]

Re: Mackie CR4 monitors

Hi, people.
I have a hypothetical question, I'm hoping to hear your thoughts.

Since these monitors use a dual 14A, 1.2A power transformer, which produces a lot of heat, which in turn is generally bad for the onboard electronics, would it be feasible to:

- remove it from the active speaker;
- remove the power cable and use its existing opening to mount a power plug;
- use an external 14V AC power transformer and plug it into the plug to power the active speaker?

Would this mod be sufficient to supply both +14V rails with an external power adaptor of, let's say, 2A current on its single 14V AC output? The bridge rectifier on the monitors PCB could be used to make that power DC. Would it be possible to split a single +14V rail to supply both +14V connections on the PCB (the three pin connector with red-black-red wires). If so, perhaps it would dramatically reduce the heat within the powered speaker and thus prolong its life and/or avoid further misbehaviour thereof. What do you think?

[UserXP]

Re: Mackie CR4 monitors

Thanks for that input. Mine were on whole day yesterday, no signs of any unwanted noise so far.
But I agree with you, I like the looks of Mackies, the driver provides very good sound - but the electronic part appears to be poorly made for the price.

[promo7uk]

Re: Mackie CR4 monitors

i had issues with mine in my studio when i first bought a set lasted about 9mnths, then did exactly the same turned out caps that diode, i removed glue had exactly the same issue,

i then moved onto M-AUDIO BX8 loads better,, better made cicruit than mackie, as mackie are over priced for what they do,

[UserXP]

Re: Mackie CR4 monitors

Well, here is an update: I bought the 1N4148 diode, soldered it in place and solder-refreshed the joints of some surrounding components where the blackened area of the board is. I assembled the speaker and it works for now, no crackling noises so far. Maybe removing the rust and glue residue also helped. I will continue to monitor the monitors to see if they are really fixed.
Thanks everyone for helping me out. It still remains to be seen whether this has worked or not.
Maybe someone else could find this thread and the experience with these CR4s useful. :-)

[R_J]

Re: Mackie CR4 monitors

I would'nt worry about series etc. just replace the caps with some good quality caps. Some people like to worry too much about .0001mohm esr difference etc. when in reality it does'nt make that much difference and its not a switching/high frequency power supply

[UserXP]

Re: Mackie CR4 monitors

Guys, I managed to find this picture labelled as an extract from the Mackie CR3 schematics. The CR3 and CR4 models share the same board, so this should apply.
Here it says that the blown diode next to the R77 really is a 1N4148. There are other marked components in its vicinity which seem to match their physical layout on the PCB itself, if I'm not mistaken. Can this schematics extract help?

But, I couldn't fing anything about these "Cap-Top" capacitors. They don't seem to have their webpage, not a word about their series, nothing. Maybe they are some industrial capacitors produced by the very factory that assembles the PCB for the speakers. Without those data, choosing the replacement capacitors will not be an easy guess.

Thank you all for participating, I really appreciate your help. Hopefully we'll manage to restore the speakers to their former glory.

[R_J]

Re: Mackie CR4 monitors

I would leave that pc board alone, It's not going to conduct anything at 12 volts, I have seen a lot worse. I would resolder the two large resistors and the two zener diodes, and either check the caps in that circuit or just replace them. The diode could very well be an ordanary 1N4148 It is hard to guess wthout any more numbers than 41 and without seeing the actual circuit. What is the board designation?????? is it D1
As for trying it without the diode, well it was'nt connected before so the amp should work.

[Chungalin]

Re: Mackie CR4 monitors

Why not a more common 1N4148 ?

To me, that blacked PCB it's way more worrying. I'd say it's carbonized around the diode and will be conductive. You'll need to scrape away any carbonized parts of the PCB before attempting repair.

[UserXP]

Re: Mackie CR4 monitors

Thanks, R_J.
No, I didn't try to turn it on without this diode, I didn't know what could happen or if it could cause another damage. Is it safe to do so?

All the glass diodes are marked with Z(number) on the board. This one is Z5, I managed to peel of some of the black gunk because it was covering the markings.
The "pop" sound was never present when turning the speakers on. I really wander how it all worked like that with this blown diode.

OK, so we have the most evidence that it is an 11V zener diode?

[R_J]

Re: Mackie CR4 monitors

I suspect when you plug in the headphones it just disconnects the speakers, as the output ic is still needed to drive the headphones.
This circuit is likely used to to keep the amp ic MUTED when you first turn on the switch, so you dont get a large POP in the speakers when you first turn on the power switch.
What is the diodes board designation? is Z? or just D? It could be a zener or it could be a regular diode.

I suspect it is a zener (11v) and once the -12v supply is at 12 volts, the diode conducts and un-mutes the amp. if the voltage on the -12v supply is less than 11v the diode does not conduct keeping the amp muted. the crackling noise could have been caused by the diode injecting noise into the mute circuit, or it could be caused by one of those caps in that circuit that is bad (dryed out but looks ok)

Have you tried the amp with the diode removed from the circuit? and if you did, is the crackling still there?

[UserXP]

Re: Mackie CR4 monitors

Yes, it traces towards the circuitry in the right corner of the PCB in that area. Interestingly, I clearly remember that mute worked when headphones are plugged in (I tried that when troubleshooting to see if the crackling noise wil be heard on the headphones as well, and it was).

I can't make out if there are any other markings on the diode, it broke in such a way that the whole negative end is completely missing together with some additional glass in its vicinity. I can see some black remnants of what may have been an additional number, but I cannot read it, it's too incomplete.

I would like to first replace that diode with a correct one to see what will happen. It may not remove the crackling sound, but it would be a start.
Should I go for the 1N4147?

[R_J]

Re: Mackie CR4 monitors

Are there another 2 numbers on the other side of the diode in your picture? If two of the numbers are 41 it can't be 1N5244b It might just be a 1N4147 glass diode.
Did you look at the picture of the board, I traced out the voltage path for the +/- voltages and that broken diode is not part of that circuit even though one side is connected to the (-) voltage supply.

Your transformer will have 3 wires from it 14vac-center tap-14vac. the center tap connects to gound and each of the other two wires connect to the bridge rectifier ~ and ~.
the output from the + of the bridge (reference to ground) will be 14v x 1.414 = +20vDC and and the - of the bridge will have -20vDC

The +- 20 volts supplies the TDA7265 output ic. each supply then pass through one of the large resistors and is clamped at + or - 12 voltsdc by Z3 and Z4 to supply the rest of the circuit. Your broken diode is NOT part of that circuit. your broken diode is part of the voltage monitor circuit
If you follow Q2 collector you will see it is connected to pin 5 of the tda7265 which is the MUTE pin.

[UserXP]

Re: Mackie CR4 monitors

I also found some interesting info on this page. But instructions are scarce, though there is some info on the incoming/outgoing voltages in the area:
https://www.mikrocontroller.net/arti...paratur_Repair

[UserXP]

Re: Mackie CR4 monitors

I tested the glue with a multimeter for conductivity, nothing showed. I did, however, peel off what I could, as in some areas the glue easily flaked. But in the other areas it was way to hard and I was afraid not to tear the components it was glued on. The two little caps look normal, not bulging on either side. Plus, the position of the board is upright, the electrolyte could not have leaked towards the diode which is on its right. Just my guessing. :-)

By tracing the paths, I see that the broken diode was connected to one of the big resistors, which in turn comes from the AC power output of the transformer. Now, the label on the transformes says that it outputs 14V. Could the defective diode be the 0.5W 14V one, or 1N5244B?

[R_J]

Re: Mackie CR4 monitors

If the diode lead has been corroded off, my first suspect would be the caps closest to the diode leaked its acid electrolyte. What are the numbers on the diode? I see `41' I suspect it could be a 1N4741 (11v zener) or it might just be a regular diode

From looking at the board view, It looks like the other 2 zener diodes are for clamping the lower +/- voltage supplies, this one that is corroded seems to feed a seperate circuit, likely Q1/Q2 . Thats why the speaker still works but was noisy, Q1 & Q2 might be muting transistors?
If q1 & q2 are connected to the amp ic's input pins I suspect that corroded diode is just used for muting the amp during power up.

[petehall347]

Re: Mackie CR4 monitors

replace the diode and remove any other glue . i would first see if the glue has become conductive . i know some does do .

[budm]

Re: Mackie CR4 monitors

Bad brown corrosive and conductive glue strikes again.

[UserXP]

Re: Mackie CR4 monitors

Hi, Khron. Thanks for the input. I am not sure I can follow the ideal scenario as I am not sure how to exactly do what you suggested (sorry for my lack of knowledge ). I will test the diodes and resistors with the multimeter tomorrow as it is kind of late now. If they turn out to read fine, could we try with replacing the diode for now and see where it will get us? But, if the method you suggested is the only way to calculate the voltage and power of the diode, then I shall have to ask for detailed instructions on how to perform the procedure.
Unfortunately, Mackie doesn't provide service manual for this specific model. Also, there seem to be additional components under the black boxy blob. I can't see the printed markings on the board for the blown diode, let alone potentially other hidden components.
I really like these monitors and the sound they produce, but their lifespan seems to be quite short.

Many thanks in advance for further assistance.