Mackie CR4 amplifier no sound

[budm]

Re: Mackie CR4 amplifier no sound

This is what I got from a Mackie service guy in the email:

"I suspect that the problem lays on the headphone mini jack placed on the front panel. We've seen before that this jack gets damaged, so the amplifier remains in the mute state". - This is probably not true because the headphone jack works normally on my original CR4 speakers PCB.

He also mentioned the L/R switch, which I determined is not the cause also.

Then he added this and included a photo I am attaching here:

Let this get checked by your service guy - short pin 4 and 5 to unmute amp.

If you look at schematic the headphone jack JK1 switch pin 4 and 5 which are used for muting when headphone is plug in, you will get the sound through the headphone OK but when the headphone is removed but the pin 4 and 5 are not making contact, the amp will stay in mute mode. So verify t hat pin 4 and 5 are making contact.

BTW, you should ask for full schematic since so may people out there have so much problem with these unit.

[UserXP]

Re: Mackie CR4 amplifier no sound

https://components101.com/ics/tda726...udio-amplifier

pin 5 is pulled low to mute it . see if that is the case here .

OK, please explain. I am to put the multimeter to DC voltage check and touch pin 5 and GND with the probes?

[petehall347]

Re: Mackie CR4 amplifier no sound

https://components101.com/ics/tda726...udio-amplifier

pin 5 is pulled low to mute it . see if that is the case here .

[petehall347]

Re: Mackie CR4 amplifier no sound

TDA7265 pin 5 is the mute pin .. some people have cut this pin and restored sound ..i would be checking its voltage first rather than cutting it . or i might desolder the pin .

[UserXP]

Re: Mackie CR4 amplifier no sound

This is what I got from a Mackie service guy in the email:

"I suspect that the problem lays on the headphone mini jack placed on the front panel. We've seen before that this jack gets damaged, so the amplifier remains in the mute state". - This is probably not true because the headphone jack works normally on my original CR4 speakers PCB.

He also mentioned the L/R switch, which I determined is not the cause also.

Then he added this and included a photo I am attaching here:

Let this get checked by your service guy - short pin 4 and 5 to unmute amp.

[UserXP]

Re: Mackie CR4 amplifier no sound

Hi, friends, thanks so much for all your replies. I'll do my best to address them all. OK, here it goes:

To: budm and petehall347

I did try the L/R switch, but it made no difference. If it were the switch, like it sometimes loses contact on my set of speakers, usually only one speaker loses sound or exibits crackling while fiddling with the switch.

The amplifier is based on the TDA7265 chip which is mounted on the big heatsink (you can see it in one of the images). Unfortunately, the PCB cannot be detached from the backplate because it is glued with that black resin, that's why it's under these weird angles in the photos. The way the speakers faded out looked to me also as if it were a discharged and not recharged capacitor. But the fading from a full normal volume to a complete silence happened in maybe less than 10 seconds, the sound literaly withered away and remained silent. Is that time symptomatic of a specific capacitor failiure or a power loss to it?

Now, on the schematics, I contacted Mackie before and their reply was "For these low budget products, schematics are available to authorized service personnel only". Nevertheless, I managed to find a portion of the schematics for the CR3 version, which shares a very similar build. If it can be of any help, please have a look.

To momaka:
The speakers use a pot volume knob, which at the same time is the On/Standby switch. When you turn it to the right, it clicks, the green power LED comes on and from there on you control the volume up. When you turn it all the way to the left, it reduces the volume and then clicks and the speakers turn off. It is not the problem because it works perfectly with the PCB in my original set of CR4.
The two empty white sockets with pins you see in the photos are for front panel connectors. The shorter one comes from the pot area and controls the volume and the green LED power status. The longer one comes from the AUX and Headphones jacks at the bottom of the speaker's front panel.

The two Red/Black detached wires power the driver, and the White/Black wires power the twitter of the right speaker. The small white plastic plug with a red and a black wire is for powering the left speaker (it goes to the back connectors for it). All the sound output connectors on the longer edge of the PCB, where the two big capacitors are located. These all look very firm, no loose contacts. The continuity check also confirms this. And since both speakers turned silent evenly, it is unlikely that all six wire connectors became loose after a couple of seconds of playback.

Somebody here mentoned that it could probably be something very simple, we just have to find it out.

[budm]

Re: Mackie CR4 amplifier no sound

Did you check the L/R switch?
https://jade.wtf/tech-notes/makie-cr4-switch/

[momaka]

Re: Mackie CR4 amplifier no sound

A bit hard to tell what's going on from these pictures alone. Would be nice if we can get straight shots from the top and bottom side of all PCBs.

That said, are there speaker output relays? If so, check those to make sure they make good contact when they switch. Although it's unlikely that they can cause audio to slowly fade away, they are worth checking out. I've seen speaker output relays with bad contacts cause somewhat similar issue (with audio sounding weaker than normal, then going back to normal, then disappearing, and etc.)

I don't think the issue would be power supply related, because if the voltage on any rail drops, you'll start to get distortion (as reduction of voltage does not mean reduction in amplification.)

On a related note, is the volume of the output regulated by a potentiometer or is it a digital scheme. If it's the former, it may be worthwhile to check the potentiometer. If it's the latter, you'd have to find which IC does the digital volume control / mixing and check that it's not being told to attenuate due to something else being faulty in the circuit... though I feel this might not be the case, because then the sound heard through the headphones should also be affected.

[petehall347]

Re: Mackie CR4 amplifier no sound

is it a chip amp or discreet ?

[petehall347]

Re: Mackie CR4 amplifier no sound

am wondering if the main rails are losing power and the music fading out is the main caps discharging

[petehall347]

Re: Mackie CR4 amplifier no sound

would need the schematic to comment further ..i am not familiar with it .

[UserXP]

Re: Mackie CR4 amplifier no sound

Thanks for the input, Pete.

Yes, I checked the transformer. It outputs both positive and negative rails, the bridge rectifier is also working fine. The 12V regulation module also works as it has an indicator LED light for both the postive and negative 12V when outputting power.

The source was my computer. I connected the amplifier to the soundcard's output jack. I also tried with a smartphone's headphone jack as a source, still nothing.
But, when the amplifier is powered on and hooked to the source and I plug the headphones on the amplifier's front panel headphone jack, I can can hear the sound on the headphones clearly.
Does that sound symptomatic of something?

If there is a bad solder, how can I detect that? The joints really look nicely done.
And the way it went silent, as if something reduced the volume steadily until zero and holds it there.

[petehall347]

Re: Mackie CR4 amplifier no sound

did you check the audio source ?

[petehall347]

Re: Mackie CR4 amplifier no sound

if both channels check power supply ..might be as simple as a dry joint or loose fuse

[UserXP]

Re: Mackie CR4 amplifier no sound

Here are some pictures of this amplifier unit.

I tried replacing the zener/resistor 12V regulator circuit on this unit as well like I did on my set of CR4s, but it didn't help. I mean, there is power and everything, but the unit still doesn't produce sound.

Now, as you can see in the photos, the PCB looks quite clean. The "green" side of it is also superb. It cannot be seen in these images, but I've inspected all the caps inside and they look normal, the date code on all of them is 2016. The area on the PCB that usually gets hot is also pristine green, no overheat or burn marks, it's like it has never been used.

Do you havy any suggestions on what could cause this sudden "muteness"? It's as if the amplifier got stuck in the mute or standby mode, and does not detect that the input signal is coming in.
Please, any help would be appreciated. I do have a multimeter, I would just welcome any step-by-step instructions on what to measure and where/how.

Thank in advance, stay safe.

[UserXP]

Hi, people.

I've got an amplifier assembly from Mackie CR4 parts. It's just an amplifier, there was no speaker housing, so I used my set of CR4s to test it.

Anyway, upon connecting everything and hooking the "new" amplifier to an audio source, the sound played clearly and strongly for the first ten seconds. I was happy it was working. Then the sound started to fade out during the playback until it was no more. After it had "dropped to zero", there were two very short intervals of sound playing at the normal volume, as if the amplifier was trying to continue, but then it cut off completely and now there is no sound coming from the set at all.

I visually checked and tested some of the capacitors and couldn't find anything strange-looking. Now, some of you may recall my previous topic on my own CR4s and the zener/resistor heat issue. This amplifier has a very clear board and the area where the PCB in mine was burnt black is perfectly clean and green in this amplifier assembly, no scorch-marks. It's as if it wasn't used much.

I'd really like to try and fix this amplifier assembly and maybe keep it as a spare one.
What is the usual cause of an amplifier volume fading out to a complete silence on its own during playback?
What should I check? I am hoping that maybe it was left in a storage for some time and maybe some of the parts weakened. Since it started the playback normally and clearly, with no hissing or crackling, there must be something that gave way during the sound reproduction.

Thanks in advance for any assistance.
Take care, stay safe.