Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Audio Equipment
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 10-17-2020, 05:06 PM   #1
UserXP
Badcaps Veteran
 
Join Date: Apr 2012
City & State: Niš, Serbia
My Country: Serbia
Line Voltage: 220VAC 50Hz
I'm a: Knowledge Seeker
Posts: 262
Default Mackie CR4 amplifier no sound

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.

Last edited by UserXP; 10-17-2020 at 05:16 PM..
UserXP is offline   Reply With Quote
Old 10-18-2020, 11:22 AM   #2
UserXP
Badcaps Veteran
 
Join Date: Apr 2012
City & State: Niš, Serbia
My Country: Serbia
Line Voltage: 220VAC 50Hz
I'm a: Knowledge Seeker
Posts: 262
Default 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.
Attached Images
File Type: jpg 20201018_190317.jpg (1.07 MB, 19 views)
File Type: jpg 20201018_190212.jpg (1.01 MB, 17 views)
File Type: jpg 20201018_190242.jpg (821.8 KB, 14 views)
File Type: jpg 20201018_190340.jpg (737.3 KB, 13 views)

Last edited by UserXP; 10-18-2020 at 11:24 AM..
UserXP is offline   Reply With Quote
Old 10-18-2020, 04:15 PM   #3
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 2,460
Default Re: Mackie CR4 amplifier no sound

if both channels check power supply ..might be as simple as a dry joint or loose fuse
petehall347 is offline   Reply With Quote
Old 10-18-2020, 04:16 PM   #4
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 2,460
Default Re: Mackie CR4 amplifier no sound

did you check the audio source ?
petehall347 is offline   Reply With Quote
Old 10-18-2020, 04:29 PM   #5
UserXP
Badcaps Veteran
 
Join Date: Apr 2012
City & State: Niš, Serbia
My Country: Serbia
Line Voltage: 220VAC 50Hz
I'm a: Knowledge Seeker
Posts: 262
Default 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.

Last edited by UserXP; 10-18-2020 at 04:31 PM..
UserXP is offline   Reply With Quote
Old 10-18-2020, 05:16 PM   #6
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 2,460
Default Re: Mackie CR4 amplifier no sound

would need the schematic to comment further ..i am not familiar with it .
petehall347 is offline   Reply With Quote
Old 10-18-2020, 05:20 PM   #7
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 2,460
Default 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 is offline   Reply With Quote
Old 10-18-2020, 05:20 PM   #8
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 2,460
Default Re: Mackie CR4 amplifier no sound

is it a chip amp or discreet ?
petehall347 is offline   Reply With Quote
Old 10-18-2020, 07:28 PM   #9
momaka
master hoarder
 
momaka's Avatar
 
Join Date: May 2008
City & State: VA (NoVA)
My Country: U.S.A.
Line Voltage: 120 VAC, 60 Hz
I'm a: Hobbyist Tech
Posts: 9,869
Default 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.
momaka is offline   Reply With Quote
Old 10-18-2020, 10:30 PM   #10
budm
Badcaps Veteran
 
budm's Avatar
 
Join Date: Feb 2010
City & State: S.F. Bay area
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Knowledge Seeker
Posts: 38,941
Default Re: Mackie CR4 amplifier no sound

Did you check the L/R switch?
https://jade.wtf/tech-notes/makie-cr4-switch/
__________________
Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
budm is online now   Reply With Quote
Old 10-19-2020, 02:01 AM   #11
UserXP
Badcaps Veteran
 
Join Date: Apr 2012
City & State: Niš, Serbia
My Country: Serbia
Line Voltage: 220VAC 50Hz
I'm a: Knowledge Seeker
Posts: 262
Default 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.
Attached Images
File Type: jpg 20201019_090703.jpg (999.6 KB, 7 views)
File Type: jpg 20201019_090718.jpg (791.4 KB, 5 views)
File Type: jpg 20201019_090731.jpg (1,005.2 KB, 6 views)
File Type: png Mackie CR3 schematic (extract).png (72.3 KB, 17 views)

Last edited by UserXP; 10-19-2020 at 02:03 AM..
UserXP is offline   Reply With Quote
Old 10-19-2020, 02:26 AM   #12
UserXP
Badcaps Veteran
 
Join Date: Apr 2012
City & State: Niš, Serbia
My Country: Serbia
Line Voltage: 220VAC 50Hz
I'm a: Knowledge Seeker
Posts: 262
Default 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.
Attached Images
File Type: png CR4 Front Panel jacks.png (32.1 KB, 15 views)
UserXP is offline   Reply With Quote
Old 10-19-2020, 05:00 AM   #13
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 2,460
Default 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 .
petehall347 is offline   Reply With Quote
Old 10-19-2020, 05:02 AM   #14
petehall347
Badcaps Veteran
 
Join Date: Jan 2015
City & State: worcester
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 2,460
Default 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 is offline   Reply With Quote
Old 10-19-2020, 05:05 AM   #15
UserXP
Badcaps Veteran
 
Join Date: Apr 2012
City & State: Niš, Serbia
My Country: Serbia
Line Voltage: 220VAC 50Hz
I'm a: Knowledge Seeker
Posts: 262
Default Re: Mackie CR4 amplifier no sound

Quote:
Originally Posted by petehall347 View Post
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?
UserXP is offline   Reply With Quote
Old 10-19-2020, 01:15 PM   #16
budm
Badcaps Veteran
 
budm's Avatar
 
Join Date: Feb 2010
City & State: S.F. Bay area
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Knowledge Seeker
Posts: 38,941
Default Re: Mackie CR4 amplifier no sound

Quote:
Originally Posted by UserXP View Post
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.

Last edited by budm; 10-19-2020 at 01:17 PM..
budm is online now   Reply With Quote
Old 10-19-2020, 01:26 PM   #17
UserXP
Badcaps Veteran
 
Join Date: Apr 2012
City & State: Niš, Serbia
My Country: Serbia
Line Voltage: 220VAC 50Hz
I'm a: Knowledge Seeker
Posts: 262
Default Re: Mackie CR4 amplifier no sound

Yes, it does make contact because the original amplifier PCB has no problems with the phonejack. It enters the mute mode when headphones are plugged in, and plays the sound again immidiately after the headphones are removed from the jack - just the way it is supposed to. So pins 4 and 5 obviously make contact on headphones plug removal.

Everything mounted on the front panel of the powered speaker works perfectly with the original amplifier.
When the same front panel is connected to the "new" amplifier, there is no sound. Therefore, it must be something on this new amplifier's PCB that's bad. The phonejacks are fine.

Last edited by UserXP; 10-19-2020 at 01:27 PM..
UserXP is offline   Reply With Quote
Old 10-19-2020, 01:31 PM   #18
budm
Badcaps Veteran
 
budm's Avatar
 
Join Date: Feb 2010
City & State: S.F. Bay area
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Knowledge Seeker
Posts: 38,941
Default Re: Mackie CR4 amplifier no sound

Then you have to verify that pin 4 and 5 are making contact all the way to the amplifier mute pin by checking Voltage (Black probe on circuit ground, red probe on pin 5) on mute pin of the IC when phone jack is in and when removed, it should change state.
Having full schematic will also help.
budm is online now   Reply With Quote
Old 10-19-2020, 01:34 PM   #19
UserXP
Badcaps Veteran
 
Join Date: Apr 2012
City & State: Niš, Serbia
My Country: Serbia
Line Voltage: 220VAC 50Hz
I'm a: Knowledge Seeker
Posts: 262
Default Re: Mackie CR4 amplifier no sound

The voltage on pin 5 of the TDA7265 is around 21V when 4 and 5 pins if the phonejack make contact.
UserXP is offline   Reply With Quote
Old 10-19-2020, 01:46 PM   #20
budm
Badcaps Veteran
 
budm's Avatar
 
Join Date: Feb 2010
City & State: S.F. Bay area
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Knowledge Seeker
Posts: 38,941
Default Re: Mackie CR4 amplifier no sound

Quote:
Originally Posted by UserXP View Post
The voltage on pin 5 of the TDA7265 is around 21V when 4 and 5 pins if the phonejack make contact.
It should change state when headphone is plugged in and out.
budm is online now   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums © 2003 - 2020
Powered by vBulletin ®
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 07:04 PM.
Did you find this forum helpful?