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MARKBASS CMD121P Need Help!

#23
KOH76401 said:
I have had an idea but I am curious to see if it will work. The amp head is blown however couldn't I just simply swap out the amp head while bypassing the crossover unit? OR could I use the still usable speaker / cab as an extension cabinet?
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Maybe, it depends on what other damage may have occurred. If there is a failure in the speaker itself, that can cause an amp to fail... it's why most shops don't test speakers on an amp that is not well protected. They don't want to blow up more amps.
 
#24
PhatBasstard said:
None of the Markbass cabs do. And I've owned a bunch.
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What's this?
Screenshot_20221215-234712.png
 
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#29
I've noticed that mentions of failures of the CMD121P combo seem to outnumber any other Markbass product. This may be because it might be Markbass highest selling product?
Mine failed with fractured solder joints on the back of the speaker output connectors. I wonder whether the vertical orientation of the head in this combo makes it mechanically more vulnerable to the significant vibrations when played even at moderate levels?
 
#30
Sparky Mark said:
I've noticed that mentions of failures of the CMD121P combo seem to outnumber any other Markbass product. This may be because it might be Markbass highest selling product?
Mine failed with fractured solder joints on the back of the speaker output connectors. I wonder whether the vertical orientation of the head in this combo makes it mechanically more vulnerable to the significant vibrations when played even at moderate levels?
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Probably not.
 
#32
agedhorse said:
Probably not.
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I can't remember reading of early failures of amps in other Markbass combos. The CMD121P is the only combo where Markbass uses this vertical amp orientation and there are many reports of failures, including mine. Discounting speaker vibration, maybe the amp internals are more susceptible to shock damage in this orientation when the combo is dropped/plonked onto the floor? As it's a small combo it can be thrown around quite easily. I think this is a possibility. Also this combo has those hard plastic interlocking corner protectors, not rubber feet, so no soft landings on hard floors.
 
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#34
KOH76401 said:
I did some investigating and it looks like the speaker inside my amp is reading 3.5 ohms. It’s an 8 ohm speaker so I have to suspect that it must be faulty. So I basically have a CMD 121 shell….
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If that’s the case, why not replace the speaker… unless there is additional damage. This is where thorough troubleshooting comes into play.
 
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#35
Sparky Mark said:
I can't remember reading of early failures of amps in other Markbass combos. The CMD121P is the only combo where Markbass uses this vertical amp orientation and there are many reports of failures, including mine. Discounting speaker vibration, maybe the amp internals are more susceptible to shock damage in this orientation when the combo is dropped/plonked onto the floor? As it's a small combo it can be thrown around quite easily. I think this is a possibility. Also this combo has those hard plastic interlocking corner protectors, not rubber feet, so no soft landings on hard floors.
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For the most part, the components don’t care how they are oriented if properly assembled.
 
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#37
KOH76401 said:
I own a secondhand Markbass CMD 121P that I absolutely love! My only issue was the tweeter was very noisy and I had seen on separate threads that simply unplugging and taping off was fine. I did that and noticed my amp switched off during a rehearsal one day. I switched it off and back on no issues. A few weeks later I set up my amp, got coffee, came back and the amp and my Morely Hum Eliminator were off.

Steps I took to determine issues:
1 - Morley Hum Eliminator did not come back on after plugging into multiple outlets on different breakers.
2 - Replaced fuse and blew three manufacture spec fuses.
3 - Took apart and noticed some burn marks around the motherboard and crossover.

Environment:
I play at my church every week using the same outlet for the past 6 years and never had any issues prior to now. I play a MIM Fender Jazz Bass through a pedal board into the CMD121P. Amp has been kept in a dry shelving unit at my church only being used for rehearsals and sunday service.

I will post some pictures of what I found. I will be honest and tell you all I am not a knowledgable amp user. I understand the knobs and what they do but as far as the insides I have no clue. Whatever information anyone has I would appreciate it.
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IME/IMO, Cheap Tweeters and X-Overs are ticking time-bombs that will eventually fry an otherwise Great Amp. The best way to disconnect a tweeter is to completely bypass the X-over. Just pulling the wires off the tweeter leaves the X-over in play and is just asking for trouble.
This is just based on my Cab blowing up my amp. After bypassing the X-over and directly connecting to my 2 X 10's, I have had years of trouble free operation.
 
#38
Sparky Mark said:
Agreed, in a static situation, but direction of dynamic impact loads is very important to stress on electro-mechanical assemblies.
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Not so much in amps, remember that many are shipped all over the world upside down and sideways without issues because shipping companies do whatever the want with packages.

Consoles in road cases travel all over the world on their backs, that puts many parts “on their side”, again with zero issues.
 
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#39
agedhorse said:
Not so much in amps, remember that many are shipped all over the world upside down and sideways without issues because shipping companies do whatever the want with packages.

Consoles in road cases travel all over the world on their backs, that puts many parts “on their side”, again with zero issues.
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I do agree but these amps will be shipped in packaging designed to protect them for the initial journey(s). Although I wouldn't put Markbass amps in the same category of ruggedness as professional audio equipment designed for a life on the road.
Anyhow, maybe this particular 10+ year old combo head has just come to the end of its life.
 

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