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MXR M87 Bass Compressor Repair - May Be Of Use To Someone?


Johnny Wishbone

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Thought I'd share this experience in case someone else has the same problem -  it might save you some hassle/cash.

A while back my MXR M87 died.  The level meter was still functioning but there was absolutely no sound coming from the pedal output.  I did all the usual quick fixes (contact cleaner on jacks, replaced footswitch etc) but to no avail.

After a bit of digging I discovered that the output op-amp in this pedal (TLC2262 in case you were wondering) has a maximum voltage of 16V.  Obviously this would normally be OK in a pedal that runs at 9V, except that MXRs "Constant Headroom Technology" feature is essentially a charge pump circuit that doubles the pedal's internal voltage to 18V.  It shouldn't take a genius to work out what therefore ensues if, like me, you're unlucky.

I replaced the TLC2262 with an AD822 (which has a supply voltage of 18V) and my pedal now lives and breathes again.  I believe MXR will fix pedals under warranty for a flat fee of £75, whereas replacing the blown chip cost me less than a tenner and a few minutes fiddling with a soldering iron (the TLC2262 and AD822 chips are both surface mount - soldering these can be tricky unless you're experienced in doing so).

It appears that mine is not an isolated issue as a quick Google uncovers many such failures, so I figured I'd pass this info on in case any other BC members' M87s suffer the same fate.  Please use or disregard this information as you see fit!

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  • 1 year later...

I was looking to buy a really good compressor last year when I came across this thread and also read about similar experiences with the MXR pedal elsewhere. I would probably have bought one, but the prospect of it potentially failing & needing an expensive repair due to costs being cut in manufacturing put me off & I went for a TC spectracomp instead.

Edited by Jean-Luc Pickguard
typo
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9 minutes ago, Jean-Luc Pickguard said:

I was looking to buy for a really good compressor last year when I came across this thread and also read about similar experiences with the MXR pedal elsewhere. I would probably have bought one, but the prospect of it potentially failing & needing an expensive repair due to costs being cut in manufacturing put me off & I went for a TC spectracomp instead.

I am now also a Spectra-Comp guy! I found the MXR a little too transparent for me. Just personal preference - the MXR was great in its own right.

Edited by Johnny Wishbone
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  • 7 months later...
On 21/05/2018 at 13:43, Johnny Wishbone said:

Thought I'd share this experience in case someone else has the same problem -  it might save you some hassle/cash.

A while back my MXR M87 died.  The level meter was still functioning but there was absolutely no sound coming from the pedal output.  I did all the usual quick fixes (contact cleaner on jacks, replaced footswitch etc) but to no avail.

After a bit of digging I discovered that the output op-amp in this pedal (TLC2262 in case you were wondering) has a maximum voltage of 16V.  Obviously this would normally be OK in a pedal that runs at 9V, except that MXRs "Constant Headroom Technology" feature is essentially a charge pump circuit that doubles the pedal's internal voltage to 18V.  It shouldn't take a genius to work out what therefore ensues if, like me, you're unlucky.

I replaced the TLC2262 with an AD822 (which has a supply voltage of 18V) and my pedal now lives and breathes again.  I believe MXR will fix pedals under warranty for a flat fee of £75, whereas replacing the blown chip cost me less than a tenner and a few minutes fiddling with a soldering iron (the TLC2262 and AD822 chips are both surface mount - soldering these can be tricky unless you're experienced in doing so).

It appears that mine is not an isolated issue as a quick Google uncovers many such failures, so I figured I'd pass this info on in case any other BC members' M87s suffer the same fate.  Please use or disregard this information as you see fit!

Hello! I recently did that. Replaced with AD822ARZ. But this not solved the problem. Now pedal has sound but compression indicatos still lit. All compression indicators glow but after about 5 minutes indicators starts to dim one by one. At that time the more release time I set the less indicators are glow and vice versa. Attack and ratio controls work predictably. Dont know what to do.

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  • 8 months later...
On 21/05/2018 at 06:43, Johnny Wishbone said:

I replaced the TLC2262 with an AD822 (which has a supply voltage of 18V) and my pedal now lives and breathes again.

Hi, I just came across this post looking for a solution for my dead MXR Compressor. Looking at the circuit board, I see two possible op-amps (U7 and U8) and I'm not sure which is the one that needs to be replaced. Can anyone help me with this?

Thanks!

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On 24/11/2020 at 17:48, kidego said:

Hi, I just came across this post looking for a solution for my dead MXR Compressor. Looking at the circuit board, I see two possible op-amps (U7 and U8) and I'm not sure which is the one that needs to be replaced. Can anyone help me with this?

Thanks!

Sorry, I no longer own the pedal to check, and I can't remember off the top of my head!

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On 14/07/2019 at 14:31, Jean-Luc Pickguard said:

I was looking to buy a really good compressor last year when I came across this thread and also read about similar experiences with the MXR pedal elsewhere. I would probably have bought one, but the prospect of it potentially failing & needing an expensive repair due to costs being cut in manufacturing put me off & I went for a TC spectracomp instead.

Off topic I know, but the TC Electronic Spectra Comp in my opinion is an absolutely astonishing pedal, and it can actually be used as an amazing subtle tone sculpting pedal too, along with compression, if that is what you want, depending on how you set the crossover, makeup gain, mix and compression parameters for the 3 bands.

Personally I very much has taken advantage of this, it just give me the final tiny touch needed to tonal perfection, actually having set it to a fairly subtle compression with some uncompressed signal blended in, it having very little effect on my playing dynamics (though definitely adding a nice amount of punch, snap and bite), but, even if also relatively subtle, a, to me at least, quite essential impact on my tone (I believe though it should be possible to still dial it in in a way so that it will affect your tone much less and do more of a traditional compressor job).

Just offers so many tweaking options if one dare diving into the Toneprint editor (I actually didn't really like any of the pre-made templates and artist Toneprints) , but even me, with a fairly layman level of understanding of compression, was able to get out of it exactly what I wanted, with some trial and error, just listening carefully to how my adjustments affected my signal and re-adjusting accordingly. 

Edited by Baloney Balderdash
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On 28/11/2020 at 23:34, Baloney Balderdash said:

Off topic I know, but the TC Electronic Spectra Comp in my opinion is an absolutely astonishing pedal, and it can actually be used as an amazing subtle tone sculpting pedal too, along with compression, if that is what you want, depending on how you set the crossover, makeup gain, mix and compression parameters for the 3 bands.

Personally I very much has taken advantage of this, it just give me the final tiny touch needed to tonal perfection, actually having set it to a fairly subtle compression with some uncompressed signal blended in, it having very little effect on my playing dynamics (though definitely adding a nice amount of punch, snap and bite), but, even if also relatively subtle, a, to me at least, quite essential impact on my tone (I believe though it should be possible to still dial it in in a way so that it will affect your tone much less and do more of a traditional compressor job).

Just offers so many tweaking options if one dare diving into the Toneprint editor (I actually didn't really like any of the pre-made templates and artist Toneprints) , but even me, with a fairly layman level of understanding of compression, was able to get out of it exactly what I wanted, with some trial and error, just listening carefully to how my adjustments affected my signal and re-adjusting accordingly. 

Incidentally, the reason I don't have the MXR any more (as mentioned above) is that I now have a Spectra Comp!

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  • 9 months later...
Guest Pramod_w
On 29/02/2020 at 19:27, Mjollnir said:

Hello! I recently did that. Replaced with AD822ARZ. But this not solved the problem. Now pedal has sound but compression indicatos still lit. All compression indicators glow but after about 5 minutes indicators starts to dim one by one. At that time the more release time I set the less indicators are glow and vice versa. Attack and ratio controls work predictably. Dont know what to do.

Hi, did you find the issue..?

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Guest Pramod_w
On 24/11/2020 at 23:18, kidego said:

Hi, I just came across this post looking for a solution for my dead MXR Compressor. Looking at the circuit board, I see two possible op-amps (U7 and U8) and I'm not sure which is the one that needs to be replaced. Can anyone help me with this?

Thanks!

Hi, topic is a bit old but the correct IC is U8

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  • 2 months later...

Hi guys,

 

I need help: Recently, I've plugged in my MXR M87 after a while (I'm not in active playing for almost 3 years now). When I put jack in input, LED's would normally all brighten and would go down in second or two, but now they stay on all the time, like I've plugged in super hot input. Changed battery, tried with few different input cables, but nothing, they are on all the time. Did somebody got that and how did you solve the problem?


I've uploaded two pics here:
 

https://postimg.cc/7G4rX6Fr


https://postimg.cc/1nKhdSSn

Edited by Ivan1981
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Found the issue with mine and it wasn't the opamp. The ratio switch was dead. The usual symptoms, no compression when engaged, leds go crazy... i fixed the existing one. It took some teethpulling in order to remove it from the board, but i made it. One of the internal sliders that make contact got broken off the rotating wheel. 

 

In case one needs to recalibrate the unit, it can be done the same way mnats 1176 or Gyraf 1176 are calibrated. You need external VU meter as the built in works in GR mode only. Audio interface or DAW software can be used for this.

Edited by Kingkorg
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  • 1 month later...
On 26/11/2021 at 18:30, Kingkorg said:

Found the issue with mine and it wasn't the opamp. The ratio switch was dead. The usual symptoms, no compression when engaged, leds go crazy... i fixed the existing one. It took some teethpulling in order to remove it from the board, but i made it. One of the internal sliders that make contact got broken off the rotating wheel. 

 

In case one needs to recalibrate the unit, it can be done the same way mnats 1176 or Gyraf 1176 are calibrated. You need external VU meter as the built in works in GR mode only. Audio interface or DAW software can be used for this.

That is interesting, the ratio switch is something I would have never suspected.

 

I am currently working on one for my bassist and I have found some more things everyone facing this issue can (and probably should) check.

 

First of all, the version of the pedal I have is a revision D, and the issue with the pedal is that there is no signal from the output and the LEDs all light up like it's latching to the power rail.

After what the OP said about the output op-amp U8, I have replaced it just in case to be safe, however, that didn't fix the issue. After many many hours of trying to figure out the circuitboard, I have found that it is much more likely that the IC responsible for the compression has died, upon which it took out a couple transistors with its last gasp. U5 is a TL064 (14-pin) 4 channel op-amp and where most of the compression magic happens from what I can tell. I still have to determine if that is actually gone (or maybe it's a problem with the selector switch, as above, tbd) but I have found 3 Transistors that had been damaged due to whatever happened.

 

Q12, Q13 and Q16 are all the same PNP type transistor and I found they had a Base-Emitter short. I have replaced those from what I guessed they were based on the SMD code, see GS code for reference in your database of choice.

(Also, almost all the SMD code markings on that board are very very weird, I haven't found some of those codes to this day...and had to do a bit of guesswork with some help of the database on yooneedone, but I haven't found a single exact marking code of any of the components on that board other than the op-amps.)

Anyway, replacing those had the effect that the latch-up was gone and I was able to see a signal at the output again, but it seems like none of the actual compression works, which is why I now suspect U5 to be faulty (and some of the signals around it were missing or really weak and weird.) So I have to further investigate this and will post when I know what else is going on in the circuit. Hope this helps so far.

 

What annoys me the most is the way Dunlop/MXR treats their customers with this issue. I have emailed them and asked if it is possible to obtain the schematic and even offered to sign an NDA, as from the previous posts I could already tell that this wouldn't be a welcome request at their end. I had even made it clear that I had already replaced and checked U8, so that this was working again and they would see that I knew what I was doing (more or less), but the response was just ridiculous. They slapped the most generic reply at me, treating this almost like an isolated incident, asking if I had isolated the pedal from everything in the signal chain (when it should have been clear that it was already opened and on my workbench, hooked up to frequency generator and oscilloscope) when they probably have a very clear idea what is wrong with their pedals.

 

Anyway, just venting my frustration, good luck to you all troubleshooting this overpriced failure!

 

Importan Update (Edit):
I have now found that Q12, Q13, Q16 are NOT PNP transistors. They are NJFETs and they very likely aren't even broken. I am very sorry for the mix up, but theis was just my initial guesswork without a proper schematic :(
So please don't act on this info, I am still trying to figure out what's really causing the issues and which bits really are or aren't broken. For now I have a little better understanding about what the circuit does, also in relation to the test points, and I will eventually try and post about it when (or if) I succeed.

One more thing: the ICs that can be found on the tiny LED board, U2, U3, U4 are all comparators and are only dealing with a DC-part coming off of the compressor sidechain to indicate the gain reduction. So it is in theory possible to get the pedal working for audio without utilising the indicator LEDs. But at this point that's not really helpful to anybody yet.

Edited by Toph
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  • 3 weeks later...

So to follow up on this, I tested the ratio selector switch in the one I am still working on and it is definitely gone. Here are links to the datasheet for everyone who wants to check theirs. It is a rotary switch by Alpha, SR1712F-0204 (datasheets: mouser, alpha) If you find yours damaged, you can try and de-solder it with the help of solder wick and flux, but I had to eventually give up with the heat gun and gave it to a more skilled colleague with solder wick.

 

More interestingly though, a pattern starts to emerge, because the switch is rated at 300mA, and so seem to be the PNP transistors, so if my theory about U5 dying was correct then it would not be surprising if it has taken out those components with it. Also if there is actually so much broken on the board it would explain why MXR just replaces the whole electronics instead of bothering to replace so many little things. And if U5 died, it raises the question how or why did it die, so I am actually not sure if there is maybe a problem with the voltage regulator circuit. I find it odd for example that I'm seeing +15V and -10V at the supply pins of U5, instead +/-15V would  have made more sense to me...

My question now is, does anybody in this forum still have an original unbroken MXR bass compressor (or maybe knows someone who has) and could they provide some readings? There are several test points on the board where the voltages can be easily checked and I have a rough idea about what kind of signals can be seen at those. So without the schematic that's more or less the best way to compare and see what else is going on in the circuit.

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  • 5 months later...

Well, I am another one of the owners of an afflicted unit. My pedal now takes 10-15 minutes to "warm up" before the compressor works correctly. When It is first turned on, the LEDs light all the way up, and the pedal is pretty much in full compression mode, even if no signal is applied at all and the pedal is not engaged. I have read some other forums where they say that sometimes things can normalized.  It sucks because I really do like how the pedal works, but waiting for 15 minutes to use a pedal is just not usable.  I've considered seeing if I could send it back to MXR for repair, as it is definitely well beyond my abilities.  My pedal is Rev D and I probably picked it up back in 2014-2015.

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9 hours ago, tbonesullivan said:

Well, I am another one of the owners of an afflicted unit. My pedal now takes 10-15 minutes to "warm up" before the compressor works correctly. When It is first turned on, the LEDs light all the way up, and the pedal is pretty much in full compression mode, even if no signal is applied at all and the pedal is not engaged. I have read some other forums where they say that sometimes things can normalized.  It sucks because I really do like how the pedal works, but waiting for 15 minutes to use a pedal is just not usable.  I've considered seeing if I could send it back to MXR for repair, as it is definitely well beyond my abilities.  My pedal is Rev D and I probably picked it up back in 2014-2015.

 

Hi tbonesullivan,

 

Sorry to hear you're having problems as well. It is still possible it's a relatively easy fix once someone's figured out what's going on. The problem is, without an accurate schematic it is quite the task... It would be good if right to repair would give us access to those or maybe someone could cause a shitstorm on MXR/Dunlops social media, so they voluntarily give out the circuit diagrams... just thinking out loud here.

 

It's interesting that it needs time to "warm up" - I need to ponder about that some more. I take it that during the warm up phase you have no sound?

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10 minutes ago, Toph said:

It's interesting that it needs time to "warm up" - I need to ponder about that some more. I take it that during the warm up phase you have no sound?

 

I have sound, but it is soft and compressed. The LEDS are showing how much compression is being used, so the pedal is pretty much stuck in full compression mode, even without any signal and in bypass. They light up right after I plug it in or attach a battery. By turning down the ratio control, I can make the signal louder, and the output / input controls still also can alter the volume.

 

Gradually the LEDs show less and less compression, and the signal gets louder, and you can start to see the LEDs react to playing. Once the LEDs are completely unlit while there is no signal, then I can hear it working correctly, and the LEDs show transient compression.

 

There was a post on talkbass about there where someone said "If their "Constant Headroom Technology™ " is a charge-pump circuit, then that may be the problem area with latch-up causing part of the internal power circuit to fail. For some this failure will "remedy" itself after a while and the comp will start acting normal again."  https://www.talkbass.com/threads/dead-mxr-m87-bass-compressor.1284462/#post-20072010

 

I may just contact MXR, who apparently will fix it out of warranty for $75 or something. It sounds like they will pretty much change out the entire electronics section, and really not say what is wrong with it. It's cheaper than a new one, but what's to say it won't happen again?

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  • 1 year later...
On 14/08/2023 at 13:41, bassace97 said:

Thanks for this! Just did this fix myself - bought one off ebay and swapped the chip for another TLC2262. A question for those that went the AD822 route: Did this different chip make any difference to the sound or characteristics of the compressor?

I can't say that I noticed any difference, personally.

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I bought a broken M87 on reverb and wanted to share my repair experience:

 

The broken unit was stuck with no sounds and all the gain reduction LEDs on.

I could get it working by shorting two pins on the ratio switch, but it didn't really compress the sound enough.

First, I first replaced the TLC2262 with a  new AD822. This did not change the problem.

Then, I replaced the ratio switch with a new one and now it works. I bought it here: https://eu.mouser.com/ProductDetail/Alpha-Taiwan/SR1712F-0204-20F0A-N9-N-027?qs=8%2Br4Hz5Xir8jgfyVwPHVzQ%3D%3D

I had to destroy the old switch to get it out (very hard desoldering job for an amateur like me).

 

Without this page, I couldn't have repaired it, so thanks a lot.

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