Mackie CR4 monitors

[Khron]

Re: Mackie CR4 monitors

Here's a silly thought - any chance there's room on the backplate to mount the transformer on the outside, using the same mounting holes? Going by the photo, there should be.

That way, you'd just have to lengthen the five wires (mains in, sec-0-sec) - might need to drill one extra hole (or two) though - and ideally add a rubber / plastic bushing, to protect the wire insulation.

[Xebozone]

Re: Mackie CR4 monitors

Hello,

My speakers suffered the same issues as is common with these around the internet.
The article linked earlier in this thread helped me identify the Zener diode (1N4742A - 12V 1W) that caused the issues.

I replaced it with a beefier one (1N5349 - 12V 5W) and cut the mute pin of the amplifier chip (TDA7265). My speakers were cracking and silent, and after, they worked great.

A few months later, the powered speaker started to go silent. After cooling down, it worked again. I noted that some of the PCB is cracked and blackened as typical with these speakers (perhaps due to the thermal expansion and contraction). I had to bypass the cracks in my board by soldering some wires across the cracks and it's working again... for now.

In that linked article above, the writer of the article mentions making a cheap circuit to bypass the poorly designed "shunt regulator". I'm interested in implementing his solution, but there is no mention in that article about how to wire-in the solution.

I'm certainly no electronics expert, so it would be appreciated if someone with some knowledge could take a look at the photos and schematic from that article and advise how to complete/wire-in the circuit replacement. What needs to be removed from the circuit (if anything)?

Thanks for your time!

[decayed.cell]

Re: Mackie CR4 monitors

So I have no sound out my CR4's and I went ahead and replaced all the diodes and the resistors, as well as all the electrolytic capacitors except the big 4700uF ones. However now I'm getting approximately 16V, -16V, +6V, +16V on the four measurement points rather than -20V, -12V, +12V and +20V. Anyone know what to do now?

[UserXP]

Re: Mackie CR4 monitors

In that linked article above, the writer of the article mentions making a cheap circuit to bypass the poorly designed "shunt regulator". I'm interested in implementing his solution, but there is no mention in that article about how to wire-in the solution.

I'm certainly no electronics expert, so it would be appreciated if someone with some knowledge could take a look at the photos and schematic from that article and advise how to complete/wire-in the circuit replacement. What needs to be removed from the circuit (if anything)?

Thanks for your time!

I second this. It could be worth to try.
I had replaced the cracked diode and the speakers were working fine for a while until recently, when the same crackling noise came back.
The writer of that article should have been more specific if his idea was to actually publish a possible solution in detail.

[UserXP]

Re: Mackie CR4 monitors

Anyway, I started getting the crackling sounds again, but they are different now. They happen a minute or two after powering up the speakers. I also heard a loud snapping sound two times, and once the right speaker lost audio. So, I opened the powered one again.

The board has developed small cracks at the place where it became blackened due to heat (this area contains two zener diodes and two big resistors). I decided to desolder them all for a test.

Caps C74, C80 and C81 are CapTop brand rated at 16V100uF. One of them is completely dead, the multimeter doesn't even recognize it being connected for testing. The other two showed 98pF. So all three are bad. C78 is 50V47uF and it reads OK.
I am going to replace them all.
I didn't remove C37 and C38 but they are 50V1uF so I hope they are fine, plus I don't have those ratings (I currently have only 50V 2.2uF and 0.47uF ones).

Is it possible to remove the two diodes and resistors from the board, insulate them and mount them to the heatsink via a daughter board or alike, then connect their leads with wires to their corresponding contacts on the main board. Would this rake the heat away from the board or not? It is probably the main source of the black area and it probably killed those caps too.

Z3 and Z4 are 1N4742A zener diodes.
R1 and R2 read 98ohm, I guess they are 100Ω load resistors. Their contact points read 20V, I guess they convert/regulate the voltage for the zeners, which in turn produce a lot of heat.

Or, are there any equivalents for these components which do not generate so much heat and therefore be good replacements to mount back on the main board?

By the way, the contact points of Z3 and Z4 show cracks in the board, probably the heat did this. It must have reached really high temperatures.
Any ideas of improving it?

[UserXP]

Re: Mackie CR4 monitors

Well, here is an update:

I managed to find a 1N4742A alternative in the form of a ZY12 (12V zener 1.3W) diode in a local hardware shop. I also found wirewound 100 ohm 5W resistors. And I used Panasonic FR series 50V47uG and 16V100uF capacitors to teplace the dead ones.

Now, I did not solder the diodes and resistors facing/near the board. I actually positioned them in a cascading manner. Looking from the bottom, the highest mounted comes the R1, then R2 5mm bellow it, then come the Z3 and Z4 diodes just bellow the R2 - but everything is above the two capacitors. Now, when the board is its normal upright position, the heat from both components will have a direct and unobstructed space to escape upwards. Hopefully, this will prolong the life of the present capacitors. Also, the slightly beefier components should not generate too much heat. And, by distancing the components from the PCB and letting the heat escape more efficiently, the PCB and the speakers should have their lifespan prolonged a bit.
Anyway, after the repair, the speakers now work great, zero cracking and popping, and the back plate is now barely warm to the touch, compared to the previous state when it would get hot after 10 minutes or so. I will continue to monitor the monitors.

Hopefully, someone will benefit from this experience as there are a lot of people getting disappointed in these otherwise great little speakers.

[decayed.cell]

Re: Mackie CR4 monitors

Well, here is an update:

I managed to find a 1N4742A alternative in the form of a ZY12 (12V zener 1.3W) diode in a local hardware shop. I also found wirewound 100 ohm 5W resistors. And I used Panasonic FR series 50V47uG and 16V100uF capacitors to teplace the dead ones.

Now, I did not solder the diodes and resistors facing/near the board. I actually positioned them in a cascading manner. Looking from the bottom, the highest mounted comes the R1, then R2 5mm bellow it, then come the Z3 and Z4 diodes just bellow the R2 - but everything is above the two capacitors. Now, when the board is its normal upright position, the heat from both components will have a direct and unobstructed space to escape upwards. Hopefully, this will prolong the life of the present capacitors. Also, the slightly beefier components should not generate too much heat. And, by distancing the components from the PCB and letting the heat escape more efficiently, the PCB and the speakers should have their lifespan prolonged a bit.
Anyway, after the repair, the speakers now work great, zero cracking and popping, and the back plate is now barely warm to the touch, compared to the previous state when it would get hot after 10 minutes or so. I will continue to monitor the monitors.

Hopefully, someone will benefit from this experience as there are a lot of people getting disappointed in these otherwise great little speakers.

Do you mind taking some photos of what you did?

[UserXP]

Re: Mackie CR4 monitors

Yes, as soon as I get the chance. I need the speaker for my work so that's why I re-assembled them immediately, not taking any puctures.
But I will take the tame to remove the back panel and make a couple of pictures. Anyway, the speakers have been working great since the repair.

[UserXP]

Re: Mackie CR4 monitors

OK, here are a few images showing what I did. The components are mounted in a cascading fashion, so the heat release is not being directly blocked by other components (when viewing, the improvised schematics should be envisioned 90 degrees rotated counterclockwise to get the actual orientation):

(R1) ===>
| (R2) ===> heat goes upward
| | Z3/Z4 =>
| | |
| | |
| | |
===============PCB

Total capacitors replaced:
3x 16V100uF CapTop SK replaced with Panasonnic FR 16V100uF
2x 10V220uF CapTop SK replaced with Panasonnic FR 16V220uF
1x 50V10uF CapTop SK replaced with Panasonnic FR 50V10uF
2x 50V47uF CapTop SK replaced with Panasonnic FR 50V47uF

Now, the original 50V47uF and 50V10uF capacitors measured OK, but because they were very close to the hot area, I replaced them anyway. The two 10V220uF measured almost 390uF, which is way off their rated value.

Now, upon longer testing, the back plate of the right speaker does get quite warm but only after several hours of non-stop operation and playing audio. I am still considering taking out the power transformer and mounting it externally in a separated case or alike, and then extending the wires to the speaker. It might actually be done in a "plug-in" fashion so that the power source can completely be separated from the backlplate if necessary. This would definitively take some heat away from the right speaker and the PCB.
But, after the repair so far, the speaker have definitively stopped clicking, crackling and cutting out.

What are your views/opinions/thoughts on the work so far?

[UserXP]

Re: Mackie CR4 monitors

I also have a question: what type of capacitors are the two 100V8.2uF capacitors that are mounted on this board? They do not seem to have the usual stripe which denotes the negative lead of the capacitor. I also noticed it sort of "bridges" the positive outputs/leads going towards the driver and the tweeter per channel (there are two of these capacitors, I suppose one is for the left channel, the other one for the right channel).

What are they and how do they cope with heat?

[petehall347]

Re: Mackie CR4 monitors

bipolar is what they are . for crossover duty i would think .

[UserXP]

Re: Mackie CR4 monitors

bipolar is what they are . for crossover duty i would think .

Thanks for that input. I have never seen a capacitor that looks like a normal one but doesn't feature a negative lead stripe.

Well, I all works fine for now. Hopefully, these speakers won't give up on me just yet, I've only had them for about three years. But, so far, we are successfully battling against the planned obsolence, thanks to good people on this forum who try to help.

[UserXP]

Re: Mackie CR4 monitors

Just out of curiosity, would it have been better if I had replaced the three 16V100uF capacitors in the hot area with slightly beefier ones, like 50V100uF? Would they have a better life span? Then again, I hope the installed Panasonic FR ones will last longer and be more reliable than the original caps.
What are your thoughts?

I couldn't find anything on the net about this original CapTop brand of capacitors, let alone their datasheet. They must be some generic industrial caps made for this specific Mackie PCB assembly purposes.

[decayed.cell]

Re: Mackie CR4 monitors

So I'm getting 0V instead of -12V on one of the diodes, just wondering if anyone know whats the problem could be now?



The 0.6V line leads from the TL074CD VCC- pin

[UserXP]

Re: Mackie CR4 monitors

People here suggested that those transistors are involved in the phonejack cutout function when plugging in the headphones.
Check the condition of the D1 diode, which is soldered directly above the R77 SMD resistor on the other side of the PCB. Mine was corroded and broken in half due to the gunk used on the PCB. The diode may be covered by the black resin right in front of the switch spongy shielding.
Also check other components for chemical damage or failure in the area, as it gets extremely hot. An acidic flux may have been used to solder some components, which might also have caused the corrosion. R1, R2, Z3 or Z4 may have died due to extreme temperatures, producing no voltage. The caps around the Z3 and Z4 diodes are probably gone too due to the extreme heat generated by the zeners and resistors. Look at my previous posts, you may find some useful insights. My CR4s have been working great since the repair.

[R_J]

Re: Mackie CR4 monitors

You likely have an open resistor (circled in red), If it is open, it could be open due to a shorted zener or something else on that -12v line

[decayed.cell]

Re: Mackie CR4 monitors

People here suggested that those transistors are involved in the phonejack cutout function when plugging in the headphones.
Check the condition of the D1 diode, which is soldered directly above the R77 SMD resistor on the other side of the PCB. Mine was corroded and broken in half due to the gunk used on the PCB. The diode may be covered by the black resin right in front of the switch spongy shielding.
Also check other components for chemical damage or failure in the area, as it gets extremely hot. An acidic flux may have been used to solder some components, which might also have caused the corrosion. R1, R2, Z3 or Z4 may have died due to extreme temperatures, producing no voltage. The caps around the Z3 and Z4 diodes are probably gone too due to the extreme heat generated by the zeners and resistors. Look at my previous posts, you may find some useful insights. My CR4s have been working great since the repair.

I replaced the diodes and all the caps on the board, so I figure its probably something else

[UserXP]

Re: Mackie CR4 monitors

Bare in mind that there are two bipolar capacitors. Did you replace those with suitable replacements?
Also check the black gunk with a multimeter, it may have become conductive and is causing irregular voltage conduit between the components.
Also check what R_J suggested.

One more thing: inspect the leads on the PCB between the resistor and the problematic diode which gives 0V. This board gradually develops cracks due to extreme heat. A crack may have developed between the resistor and the diode, thus leaving the diode unpowered. If this is the case, locate the crack and attempt to mend it. The easiest way to spot it is to turn a flashilight on from the other side of the board. Where you see the light coming through is the place where the crack exists. Scrape the green coating over the leads around the ceack, apply flux and put a bit of solder on top of it, it will reconnect the severed leads. My board also developed cracks, so maybe this experience can help you, too.

[UserXP]

Re: Mackie CR4 monitors

Hi again, friends. I need your advice. I am thinking of replacing this original "resistor/zener voltage regulator" with a separate PCB, something like this:

+/-12 regulator (as in the picture)

Now, I would need some help on which parts should I remove from the speakers PCB (resistors, zeners and possibly some caps) and I would need assistance with connecting the leads. Now, this regulator operates on alternating current input. My guess is that I can connect its "input port" to the the positive input before the + resistor, and the negative input before the - resistor from the speaker's PCB. The ground seems to be common for both input and output on this regulator. But where would I have to connect the regulator's +12 and -12 output wires to the speaker's PCB?

I can label the components on the PCB as soon as get the chance if you need that. But first I would like to know what are you thoughts on this solution. Would this generate less heat, and would the regulator work OK in an enclosed casing of the speaker? I know that I would have to mount it somewhere inside, but that would not be a problem as it has four screw holes which can be used with standoffs or something like that for mounting.

[Xebozone]

Re: Mackie CR4 monitors

Hi again, friends. I need your advice. I am thinking of replacing this original "resistor/zener voltage regulator" with a separate PCB, something like this:

+/-12 regulator (as in the picture)

Now, I would need some help on which parts should I remove from the speakers PCB (resistors, zeners and possibly some caps) and I would need assistance with connecting the leads. Now, this regulator operates on alternating current input. My guess is that I can connect its "input port" to the the positive input before the + resistor, and the negative input before the - resistor from the speaker's PCB. The ground seems to be common for both input and output on this regulator. But where would I have to connect the regulator's +12 and -12 output wires to the speaker's PCB?

I can label the components on the PCB as soon as get the chance if you need that. But first I would like to know what are you thoughts on this solution. Would this generate less heat, and would the regulator work OK in an enclosed casing of the speaker? I know that I would have to mount it somewhere inside, but that would not be a problem as it has four screw holes which can be used with standoffs or something like that for mounting.

Yes please. That is what I purchased (and what the article I mentioned suggests making). Would like to know how to wire it all in too. My speakers are collecting dust