Mackie CR4 amplifier no sound

[momaka]

Re: Mackie CR4 amplifier no sound

I unsoldered one leg of capacitor C39, labelled as 50V1uF. The ESR meter displays:

965nF
ESR=1.5ohm
Vloss= 0.4%
...
To me, the ESR data looks normal for a capacitor with those ratings.

Yes, both ESR and capacitance look normal.

However, the problem with many of the cheap crap brands is that their leakage current can go high once voltage is applied. Well, that can happen to any electrolytic capacitor, really. But it just happens more to the cheap crap brands.

Does this capacitor need to be 1uF? I have Panasonic 50V2.2uF I think FR series at my disposal. Will it be fine to use it, or should I go for the original 1uF?

No, the cap doesn't have to be 1 uF. The higher the capacitance, the slower the amplifier will switch between STB, Mute, and Play operation. So with around 2x higher capacity, you'll probably get 2x slower transition between these states... which you should not notice at all, because even with the 1 uF cap, the switch between the states is almost instant. So with 2.2 uF, it will be "slightly less instant" (that's a highly technical term, OK. ) I'll give an explanation of what C39 does a little further bellow.

If yes, what brand/series would you recommend for a cap of this function and this close to the heatsink?

Any brand and series will do.

However, because these caps are close to the heatsink and are exposed to heat, I'd suggest going with 105C -rated caps. GP 105C caps will probably be fine, but the Panny FR you have should be a nice treat, since those are quite reliable and long life.

At this point I would get a couple 1uF for this unit and the working unit since more likely the one in working unit will fail later on as well

+1000

In fact, I suggest getting as many of the caps replaced as possible, especially the ones in the hot areas. All the caps look like no-name cheap brands, and sooner or later they will fail. So probably a good idea to recap the working unit, too.

What I don't understand is that one pad of C39 measures +20V and the other (the one on pin 5 lead) measures +13.90V. What kind of a capacitor is this, how can it have two positive supply rails?

So, the function of this cap is kind of similar to C74, except instead of providing a delay (by taking time to charge through a resistor) for the power-on mute, it provides a delay when the amp is switched between STB/Mute and play when the headphones are plugged or unplugged. Otherwise, going abruptly between these states could cause crackle to be heard through the speaker, as you noticed already.

Just remember this: capacitors act sort of similar to very tiny tiny batteries in the circuit and as such, they don't like to allow sudden voltage changes across their terminals. So whenever something in the circuit tries to change voltage abruptly, the capacitor will smooth that voltage change into a more gradual one. When you add a resistor in series (in the case of C39, it's resistor R91 and C-E junction of Q2), the change of voltage across the terminals of C39 becomes even slower/"smoother". So this allows the amp to go more slowly between STB, Mute, and Play operation.

I guess the temperature might be influencing the capacitors. They are some "Cap-Top" brand, all of them. The small ones are especially prone to drying due to heat.

Yes, no-name / crap brands and heat don't mix well. I find that in a lot of 90's and 2000's budget/mid-tier audio gear, if there are any no-name or crap cap brands, the ones located closest to any heat sources are usually the first ones to fail. And even the ones that aren't can sometimes fail too. Like you noted, it kind of varies with the batch. So you can have the same cheap brand of caps last a long time in one unit and fail rather quickly in the next. For this reason, I always recommend to use only Japanese capacitors from the big 5 (Panasonic, Rubycon, Nichicon, United Chemicon, and Sanyo/Suncon) - at least if you don't want to have to do this repair anytime soon in the future again.

I'd like to put one that is similar to the other caps: black sleeve, white lettering and a cros vent. Of course, this is just for rare visual purposes.

How about replace the rest of the crap caps with good ones then? That's one way to get a more "uniform" look.
In all honesty, though, I don't know why you should care about that. Unless the unit has a clear window with lights inside pretty much begging people to stare... you're just not going to see the insides again. So IMO, you should put whatever cap brand actually does the job reliably rather than focus on the looks.

Otherwise, if you want some really cool-looking caps, I have some bright-yellow CapXon KM caps from an Apevia PSU. They look kind of catchy with their yellow sleeves... but no telling when they will fail (well, some of them have failed already, which is why I removed them all and replaced with good Japanese brands.)

[UserXP]

Re: Mackie CR4 amplifier no sound

Momaka, thank you for this informative post and all the help, especially your patience, really from all of you. I must have asked all sorts of noob questions and thank you for making concrete, clear and wise input on them.

You are absolutely right, changing all the caps would probably be the best step. I was thinking about that when I had issues with my original working unit, but then somebody posted that they replaced all the caps and got weird voltages in some areas, so I was reluctant, especially since I managed to solve the problem. I guess in each build there is a bad cap and it's a lottery which area it's going to appear in. I will need to examine all of the caps on this PCB. Some are quite obstructed by other components and many are glued, all this hiding their ratings. And of course the looks is not an imperative, I'm just so happy we got this thing working again.
I will order some other ratings of FR caps if I can find them on Farnell. Hopefully, I will find most of the caps values on those segments from the schematics.
I will look tomorrow for some Panasonic 50V1uF caps and order them.

[UserXP]

Re: Mackie CR4 amplifier no sound

Guys, just an update on this. The problem was definitively the C39 capacitor. I had Panasonic 50V2.2uF FR version, but I wanted to stay within the amplifier's specs. So since you mentioned it can be a general purpose capacitor, I found some Rubycon 50V1uF 105C 5000 hours YXF series capacitors on the local Farnell website and ordered them. I am delighted to say they have arrived and I have installed one today. The amplifier works great now and hopefully this cap will cope well with the heat the amplifier produces. The voltage on the mute pin now hovers around +13.72V in play mode, which is great! Thank you all so much, for identifying the part, and especially you momaka for your thorough and patient step-by-step instructions.

[momaka]

Re: Mackie CR4 amplifier no sound

No problems!

Rubycon YXF is actually one of the most entry-level low-ESR series, so it is better than regular GP caps. Better yet, it's still rated for long life (5000 hours for 16-100V rated caps in 6.3 mm dia. or smaller... and more for bigger caps), so that's actually a pretty good choice.

Should replace the caps now in the good unit too, while you're at it and still remember what the issue is, rather than try to figure it all out again some years down the road. And you'll probably have more peace on your mind knowing it's been fixed properly too.

[draganocap]

Re: Mackie CR4 amplifier no sound

Folks,

thank you all for your patience, knowledge and persistence. You really made my day, I was trying for some time to get it back to work (CR5), installed a different power supply as the zener diodes and resistors burned the pcb badly but ended up with a unit working shortly and afterwards short pieces of sound only when pulling out the aux jack. I replaced some other caps around the burned area, killed R88 and replaced it but removal and replacement of C39 changed the game! I just couldn't cut Pin 5, it made me feel like loosing.

Thank YOU!

[UserXP]

Re: Mackie CR4 amplifier no sound

Momaka, I followed your advice and replaced all the small capacitors in the hot area: 3x50V1uF Rubycon YXF and 3x16V100uF Panasonic FR. I didn't replace other caps. The amplifier works as with the previous repair (replaced C39), but at least now it should be good to go on the long tun.

Mackie CR-3/4/5 owners: do not throw away your speakers. Follow this topic and the awesome help people here are willing to offer and share. Replace the problematic capacitors with quality ones and introduce a LM7x12 voltage regulator module instead of the original zener/resistor solution. It will eliminate one of the heat sources and the capacitors will leave longer. This will also save the PCB from burning. And you'll have these great desktop monitor speakers working fine again. Mine still do.

[Discharged_Cap_On_Thumb]

Re: Mackie CR4 amplifier no sound

Hello. I came across this thread when trying to diagnose a pair of CR3's that exhibit the same behavior of no sound through the speaker but still has sound through the headphone jack.

I didn't want to cut PIN 5 because that seems like a crude workaround, but I must say I have no practical experience with electronics. I do the necessary tool though and consider this a first project -- the speakers already don't work and have a replacement, so if they are damaged in the process (though I'd like to avoid it) it is no big loss to me.

I wanted to try replacing C39 and have located it on the board, but before I go touching things I wanted to know a safe way to discharge the entire device first.

I once accidentally rested my thumb on the top of a capacitor, in a fully charged Camera Flash (while repairing a plastic zoom screw that jumped its groove). To say the experience was shocking would be an understatement, so I would rather avoid such experiences again.

[UserXP]

Re: Mackie CR4 amplifier no sound

Hello. I came across this thread when trying to diagnose a pair of CR3's that exhibit the same behavior of no sound through the speaker but still has sound through the headphone jack.

I didn't want to cut PIN 5 because that seems like a crude workaround, but I must say I have no practical experience with electronics. I do the necessary tool though and consider this a first project -- the speakers already don't work and have a replacement, so if they are damaged in the process (though I'd like to avoid it) it is no big loss to me.

I wanted to try replacing C39 and have located it on the board, but before I go touching things I wanted to know a safe way to discharge the entire device first.

I once accidentally rested my thumb on the top of a capacitor, in a fully charged Camera Flash (while repairing a plastic zoom screw that jumped its groove). To say the experience was shocking would be an understatement, so I would rather avoid such experiences again.

Hello. Thank you for reading and finding this thread useful. Don't worry about not having experience, I was in the same shoes and have learned a lot from the people on this great forum.
Since CR3s and CR4 use practically the same PCB, what you read in this thread will likely be applicable to your CR3 set as well.

Now, you needn't worry about discharging anything. When the speakers are plugged into the mains, they immediately start converting power even if they are turned OFF on the volume knob switch (kind of a standby mode). So, once you unplug them from the wall socket, the amplifier chip will quickly drain the remaining power from all of the capacitors. Plus, the operating voltage of the unit after rectification is around 20V, which is not strong enough to cause electric schock. But, like I said, unplug the speakers and wait for about 10 seconds and everything will get discharged by itself.

Now, since your set is exibiting the same "no sound" problem, here is what you could start with:

First unsolder C39 and then test your speakers. If they start to produce sound again normally, then the 12V regulating circuit is still functional. If you wish to retain its original design (which I don't recommend), replace the three 16V100uF capacitors there as well, since the heat in that area has probably damaged them. Mind you, this area of the PCB will then continue to heat up and will eventually burn and crack, causing more failure.
If you still don't get any sound after removing C39, one or both zener diodes or surrounding components may have failed due to extreme heat. You should replace them too - if you wish to retain the original design.

Anyway, if C39 is the issue, a full repair would be to:

1) replace all three 50V1uF capacitors
2) replace all three 16V100uF capacitors
3) remove the two zener diodes and R1 and R2 resistors and introduce a LM7x12 combo solution to remove the heating from that area of the PCB and it will continue to work for a long while.
4) optionally, replace the two 10V220uF capacitors at the upper area of the PCB. These are too small for a 220uF capacitance and will quickly dry oout due to heat, plus they probably have large resistance due to their small size. Replace all of the listed caps with some high quality long-life Japanese capacitors. I went for Rubycons and Panasonics and I haven't had a "no sound" issue ever since.

Let us know the results.

[Discharged_Cap_On_Thumb]

Re: Mackie CR4 amplifier no sound

Thank you, UserXP, for the detailed information.

I just ordered some items to help in my task (canonical tip for my Weller iron, Solder Wick, etc) that won't come for another week. I'm excited to give this a try and will keep your posted on either success or failure.

[UserXP]

Re: Mackie CR4 amplifier no sound

Thank you, UserXP, for the detailed information.

I just ordered some items to help in my task (canonical tip for my Weller iron, Solder Wick, etc) that won't come for another week. I'm excited to give this a try and will keep your posted on either success or failure.

Great! Like you said, you have nothing to lose - but, since the no sound issue with these CRx speakers is quite widespread, it is likely that you will be able to fix them. If you haven't done so already, take a look look at my other topic about the CR4s, there you will find how I implemented the LM7x12 daughter board:

Mackie CR3 monitors - Page 4

[UserXP]

Re: Mackie CR4 amplifier no sound

You see, the no sound occurs when to much voltage is being apply to the TDA7265 amplifier chip on Pin5 - which is the Play/Mute pin. When there is voltage difference betwen the input voltage and the voltage on that pin (which is like 6-7V difference), the amplifier enters the Play Mode and you can hear the sound. When the voltage is equal to the input voltage (around 20), the amplifier chip goes into the Mute mode - that is why cutting Pin5 re-enables the sound, but then you lose its intended pourpose: to mute the speakers when you plug in headphones, and to minimize the loud pop sound that would be heard when you turn the speakers ON or OFF due to pre-amp activation and capacitors discharging. Of course, we want to keep this intended pusrpose.
But, due to a faulty 12V regulation circuit with zeners and resistors, which is involved in dividing that voltage to around +/-12V, and especially when C39 leaks current (it is connected to both Pin5 and Ground), this capacitor starts to slowly leak those 20V onto Pin5 which would normally be at ~13V in Play mode, effectively muting the amplifier.

The LM7x12 combo board is very dynamic in regulating the input voltage to +-/12V and doesn't heat up almost at all, which saves the PCB from burning and the small capacitors from failing as there is one less heat source inside the speaker. Can you imagine the temperature the original regulation circuit produces when it burns the PCB to a blackened state? A potential file hazard.

Don't forget to post some images of your speakers' PCB after disassemblying them, and of your work.

[Discharged_Cap_On_Thumb]

Re: Mackie CR4 amplifier no sound

Hello. Today I got all the parts I needed to work on this. And I managed to unsolder C39. However, there is still no audio from the speakers. Yet the headphone output on the front of the speaker still functions. The input does too for that matter.

So there is no gain, yet there is no loss either.

When I first opened them up, I noticed a half dollar sized darkened blotch above C39 ( where some rather large caps are located -- you can kind of see it at the top of the image attached) on the back of the board. I suspect this amp cooked itself at one point possibly?

Now I think it would be a lot of time and possibly money to go through replacing everything, and I'm not quite ready for that task. In any case, I wanted to share a followup.

I'm not really bummed though as I learned a lot. I must admit I initially desoldered the wrong pin, but was able to solder it back (in the attached photo). Plus I learned about solder wicking, solder pump, and very basic soldering techniques.

[UserXP]

Re: Mackie CR4 amplifier no sound

The re-soldered diode looks fine, good job on that. Did you completely take out C39? In you image, it still soldered on.

The black area is the burned PCB where Z3 and Z4 are. They are 12V, but receive about 20V. So, the remaining ~8V are disipated as heat. The two big resistors help do that. However, the diodes permit only 12V and get super hot in the process. It is possible that they burned out so there is nothing to produce the required 12V. Also, inspect the traces at the burned area. Intense heat can cause the PCB to crack. If the crack separates a lead, the connection is broken.
Don't give up. You already can't use the speakers, so you may as well practise. If you have a multimeter, check voltages at R1 and R2 points when the amplifier is ON. You should get around +20V on one end and +12V on the opposite end of the same resistor. The other resistor should give you roughly the same values, but for the negative polarity. This test will tell you if the zeners are still producing 12V or not.

[Discharged_Cap_On_Thumb]

Re: Mackie CR4 amplifier no sound

Thank you.

Yes, I completely removed C39 before testing. This image was taken before that task.

I find it interesting that the headphone output, on the front of the speaker, still works. Even without C39. It's like nothing changed with the removal of that cap.

But I'm not really in the mood to work on it at the moment. However, I have bookmarked this thread and will work on it more when I have more time. I think I do need to use my multimeter and check voltages next. That will be more learning/practice.

I'm a bit afraid to use a multimeter with the amp plugged into the wall and turned on. I will have to research how to safely do that. That is safe right? Seems dangerous to me. Electricity frightens me, esp after discharging the cap that one time into my thumb.

[UserXP]

Re: Mackie CR4 amplifier no sound

I'm a bit afraid to use a multimeter with the amp plugged into the wall and turned on. I will have to research how to safely do that. That is safe right? Seems dangerous to me. Electricity frightens me, esp after discharging the cap that one time into my thumb.

You are welcome, it can be an interesting learning experience - and, you may actually fix your speakers.

Yes, don't worry, the mains power is completely isolated. It goes through the cord, then through the black switch on the back and then to the power transformer through a fuse. Plus, all the soldering is covered by that black resin glue. So nowhere on the PCB is there a 120-240V power. The only voltage going through the board is that provided by the transformer, which is dual 14V (~20V total). We need the speaker to be plugged in and turned on to produce power in order to measure the voltage. When checking voltage with your multimeter in DC voltage mode, of course, put the black probe anywhere on the Ground, and the red probe on the spot that you wish to check the voltage on.

[UserXP]

Guys, sorry for bumping this old thread, but I just wanted to let everybody involved in resolving the issue I had with this Mackie CR4 amplifier know that it is still working great! Cheers everyone!