Mackie CR4BT speaker repair

Thread Starter

Agostino44

Joined Jan 21, 2024
7
A friend of mine has a Pair of the CR4BT. And they had no power. Noticed an area that was almost burnt. So I checked to see if Z3 or Z4 shorted. Yep Z3 shorted, no +12 volts. Also found C80 had a slight dis-color and top was not mushroomed up but it looked different. Replaced both C80 & C81. I could not find schematics for the CR4BT version even contacted Mackie and they don't have the schematics for the version I'm trying to fix. The CR3 schematic is kind of close but R1 & R2 say 220 ohms. But on the CR4 they are 100 ohms 2 watt resistors. Found pictures of the board I have on the FCC web site. They didn't have schematics but they did have pictures of the board and it was an exact match. And R1 & R2 are 100 ohm 2 watt resistors. The FCC ID I looked is 2AD4XCR4BTCR5BT. First 5 characters are the company ID and the rest is device. So for anyone looking up info on any electronic device check here: https://apps.fcc.gov/oetcf/eas/reports/GenericSearch.cfm . Hope this helps anyone else!! Speakers sound great!


Hi to everyone!

I own a pair of CR4BT speakers, they stopped working few years ago, I always told myself to open them and repair them myself seeing the cost of the Mackie fixing.

Opening them I saw as everyone here a burnt area, circle on the PCB (image 1 and 2), R2 was totally burnt and already loose, it unwelded itself due to heat I guess and wasn't attached to the PCB anymore, I thought that R2 was the source of the problem. ( as you can see the Zelners in the area look fine, the burnt area center's is R2.

1.jpg2.jpg

I am currently trying to get a new R2 to replace it, and make some other welding work to try to fix the PCB.
The only thing that is not clear to me are the resistors values. as DavidLvNv said before, on the only schematic we have from the CR3 R1 and R2 are 220 ohms 2W.
If I'm not wrong my R1 is a 100 ohms +-5% (BROWN, BLACK, BROWN, GOLD, see image 2 and 3) and the R2 that I'm holding in my hand is a 3 bands 22 Ohms +-20% resistor (RED, RED, BLACK, see image 4). right?

3.jpg4.jpg
On all forums and websites that talk about this problem no one ever mentioned a 3 bands 22 ohms resistor as R2, that's why I can't understand why it's here and if it's the good one xD, did they fail to put the good resistor when manufacturing it? Did the retailer I bought it from (bought it as new) opened them to fix them and failed to put the good one?

So I need help! Should I replace it by a 100 ohms +-5% as the R1 is? Should I find a 3 bands 22 ohms one? (btw I can't even find those 3 bands +-20% on internet, seems like it doesn't exist xD)

Thank you for your help!
 

MrChips

Joined Oct 2, 2009
30,814
Replace both R1 and R2 with 220Ω 2W ±5% or ±10% resistors (even ±20% would be fine).
Measure the voltage on both legs of R1 and R2 with respect to GND.
Post your voltage measurements back here.
 

Thread Starter

Agostino44

Joined Jan 21, 2024
7
Hello MrChips, thank you very much.

I'll try this! I am quite on amateur, what does GND mean?

I'll probably do it next week I need to buy everything to do it!
 

Thread Starter

Agostino44

Joined Jan 21, 2024
7
Replace both R1 and R2 with 220Ω 2W ±5% or ±10% resistors (even ±20% would be fine).
Measure the voltage on both legs of R1 and R2 with respect to GND.
Post your voltage measurements back here.
Did you see the cracks on the PCB? Should I just replace R1 and R2 or as well try to repair the pcb with some welding?
 

MrChips

Joined Oct 2, 2009
30,814
In English the word "solder" is used instead of "weld".

1705855551465.png

The word "weld" is used when joining heavy metal parts such a metal hand rail as in gas welding or electrical arc welding.

1705855473962.png


Joining copper pipes with solder is called "brazing"

1705855401185.png

GND means GROUND or COMMON or reference point. Any metal part of the chassis will do.

Turn the board over and examine all the copper traces on the board where there are cracks.
If the copper tracks are broken you will have to bridge the tracks.
Scrap away the coating on the tracks down to bare copper. Use single strand jumper wire and solder the wire to the copper track in order to bridge the gap.

On the voltage measurements at R1 and R2, we are expecting to find +12VDC on one leg of R1 and higher voltage on the other leg. At R2 we expect to see similar values but negative voltages.
 

MrChips

Joined Oct 2, 2009
30,814
Yes, I can see that you have some major PCB restoration to perform.

Mackie CR4 broken PCB.jpg

If you can scrape away the green coating (solder resist) at the break, you can try creating a bridge with a thick layer of solder.
 

Thread Starter

Agostino44

Joined Jan 21, 2024
7
Yes, I can see that you have some major PCB restoration to perform.

View attachment 313285

If you can scrape away the green coating (solder resist) at the break, you can try creating a bridge with a thick layer of solder.
Thank you very much for your help! Sorry for english mistakes it's not my native language x)

Btw, I am totally amateur it's the first time I'm doing an electronic reparation, should I scrape and bridge all the darker lines that are broken or burnt? Or as well whiter marks and signs?

I was thinking the white signed and marks are just here as legal information for the PCB, or are they important and indispensable to make everything function fine?

Thank you very much you're very helpful!
 

MrChips

Joined Oct 2, 2009
30,814
Ignore the white printing. Pretend that they are not there.
Scrape away at the breaks and join with solder. Any gap wider than 0.5mm should be bridged with a piece of wire if solder does not bridge the gap.
 

Thread Starter

Agostino44

Joined Jan 21, 2024
7
Ignore the white printing. Pretend that they are not there.
Scrape away at the breaks and join with solder. Any gap wider than 0.5mm should be bridged with a piece of wire if solder does not bridge the gap.
Fine! Thank you very much! I'm gonna be trying that next week!

I'll let you know how it's going!
 

MrChips

Joined Oct 2, 2009
30,814
After bridging the breaks on the solder side, you could add physical strength by bonding the breaks on the component side with 2-part epoxy glue.

If the board is in danger of falling apart, glue with epoxy first before scraping away.
 

Thread Starter

Agostino44

Joined Jan 21, 2024
7
Hey MrChips!

I just replaced both of the resistors, I've put as said last time 2 220ohms 2V 5% resistors as R1 and R2, I measure on one leg of R1 13VDC and 22VDC on the other leg respect to the biggest electrolytic capacitor's GND. On R2 I measure -22VDC on both legs.

after various measurements I feel like C68 and C69 are burnt, broken, when I test their resistance with no power, nothing appears on the multimeter's screen, other capacitors give me a value as I test them in ACV (I have no generator i plugged normally on the house circuit), these 2 doesn't.

I don't really know how usefull and accurate is this information about the capacitors, others don't give me any resistance value, other does, but here it is. C68 and C69 are at the center of the burnt area, when I test R2 as well in ACV I have no value, but R1 does give me a value.

When I test in DCV on the same ground as I tested R1 and R2, C69 doesn't give any value, one leg of the C68 gives 13VDC.

I didn't do any PCB restoration for now, let's try everything on the components before doing anything on the PCB maybe?

If you look closely on the PCB you can see that the circuit that goes from the top of C69 and C68 are totally burnt witht the shape of the circuit, maybe here is a part of the issue? It's only an idea, i don't have a clue^^

Here are the information I have^^
 

Thread Starter

Agostino44

Joined Jan 21, 2024
7
After bridging the breaks on the solder side, you could add physical strength by bonding the breaks on the component side with 2-part epoxy glue.

If the board is in danger of falling apart, glue with epoxy first before scraping away.
Hello Mrchips, are you here?^^
 
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