Reviews and questions about the entry-level MPC500
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By DjDiskmachine Sat Jan 05, 2019 4:54 pm
Yo!
Bad luck you managed to pinch the cable, I recommend shrinkwrap or electrical tape to fix that!

Hmm what caps did you replace again? I'm not having any problems with my inputs, they used to have a bad noise problem but now they are pretty much transparent.
I can't see any evidence that the line in caps should need replacement, the ones I see in the Service Manual are only there for DC blocking and perform no filtering.
The line in circuitry uses a different OP amp than the outputs (IC19 as opposed to IC11 for outs). It uses the same rail (5V) as the one supplying the output amplification circuitry. Are you sure you replaced all the caps? Are you sure you got the right values in the right place?

The only thing different between the input OP and the output OP is they have their own cap for HF filtering (on the input OP that's C46, seen way at the bottom right of the last page in the Service Manual).
This doesn't seem like a likely cause of the problem to me, but can't be ruled out of course since I can't perform any measurements ;)

This sentence got my attention now when I read your post again, can you elaborate, please?
NearTao wrote:"If a sound is playing it is okay and the noise floor seems to cut out"


Do you mean that the noise is supressed, like when doing compression -eg the louder sound "pushes" the quieter noise down then the noise is louder again after the sound stops playing?

/M
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By NearTao Tue Jan 15, 2019 1:33 pm
The noise you quoted would best be described as ducking I suppose. There is a low level noise that goes nearly silent while playing a sample.

One thing I believe I have narrowed down the problem to seems to be that when plugged into the outlet I have tons of noise issues, but when on battery power they all appear to go away. I suspect the next piece of the puzzle is to get a new power pack, the one I have is Sino-American model:A31250. I'll try to keep narrowing down the issues :)

As to the capacitors I used Nichicon ULD1C101MED1TD/493-14722-1-ND and UVY1C221MED1TD/493-12895-1-ND that I ordered from DigiKey.
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By DjDiskmachine Wed Jan 16, 2019 9:11 am
OK I guess that a badly filtered PSU might be the cause of this problem, get one that's a little less cheap and report your results! :)
Please double-check your Cap values for C907 & C910, these are the ones that perform filtering for the rail Mainpow +5V in the service manual and they should be able to take care of this.
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By NearTao Thu Jan 17, 2019 4:39 pm
I have to give it to you... you know more about electronics than I do... which is probably why I went into management :)

Anyways... to clarify for future readers... the PSU was *NOT* the problem. I realized this when it started acting up with the batteries in it. I stripped the 500 back down to check the solder joints (all look good), and the caps (all look good)... and was left with that tweaked wire, and an odd behavior when I would mess with the volume knob. I re-taped the battery line in case that was causing a problem and rerouted it so it wouldn't get pinched again.

I ended up finding that if I flexed the volume/q-link board a little while it was powered that the hum would change. I ended up reseating all of the cables, which helped, but the noise instantly went away when I just put the board back where it was supposed to be. I'm not sure if it needs a circuit to the case, but on the bottom of the board there is some exposed copper on one of the posts for the case. It's possible I hadn't screwed this down well enough to the case, and the reason the noise was going away when I pushed on the volume knob was that it was re-establishing the circuit.

So... I've screwed everything down tight and will continue to give this thing a workout for the next few days.

EDIT: Also going to add, still definitely getting line noise. I thought I could hear it ducking, but normalizing and playing back some recordings it is definitely there. I tried powered, battery, as well as line and mic levels. It is there and not going anywhere.

EDIT 2: Oddly the record gain doesn't change the sound at all, but the main volume does control how loud it is... strangely, recording with the record gain down, normalizing the sound you can definitely hear it... whatever it is :/
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By DjDiskmachine Tue Jan 22, 2019 2:33 pm
Hehe.. I'm not trying to show off mah skillz here or anything, I'm just attempting to make it a little more clear for anyone that's debugging their hardware and to simplify the process of reading schematics and problem solving.

I'm impressed with your tenacity, good job on finding the broken circuit to the ground plane!

I'm curious about this comment:
"Oddly the record gain doesn't change the sound at all, but the main volume does control how loud it is..."
Do you mean that sampling with the master volume down produces a sample that is less noisy?
Do you hear this noise when auditioning before actually sampling?

Together with a colleague we're leaning towards a problem with the VMID reference, which is a common "ground" of the audio codec which handles all audio I/O before the CPU.
This should be approximately 1,65 V reference to ground. If you have a multimeter, this can be measured between the battery ground and pin 1 on the rec gain pot.
I'm pretty sure that one or both of the DC-blocking Caps from the Output OP have gone bad. These are C19 & C38 of 22uF, the two slimmer ones slightly to the left of this pic: https://www.instagram.com/p/BY_oUn0nSuF/

Might have to update the guide thanks to you! ;D If you can find the time and energy to investigate further, please report your results!
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By NearTao Wed Jan 23, 2019 8:01 pm
DjDiskmachine wrote:Hehe.. I'm not trying to show off mah skillz here or anything, I'm just attempting to make it a little more clear for anyone that's debugging their hardware and to simplify the process of reading schematics and problem solving.


I'm just a hack with a soldering iron. You'd cringe if you watched how I did the work. I used to have a great iron back when I was a kid, and patience to read and think about schematics... now I just poke "hot pointy thing here".

DjDiskmachine wrote:I'm impressed with your tenacity, good job on finding the broken circuit to the ground plane!


I know enough to be dangerous, but not get myself electrocuted.

DjDiskmachine wrote:I'm curious about this comment:
"Oddly the record gain doesn't change the sound at all, but the main volume does control how loud it is..."
Do you mean that sampling with the master volume down produces a sample that is less noisy?
Do you hear this noise when auditioning before actually sampling?


Well that was poorly worded on my part. What I probably should have said was the main volume controls the output to the headphones (as expected), but no, it doesn't reduce the noise when sampling from audio. Hopefully that makes more sense.

DjDiskmachine wrote:Together with a colleague we're leaning towards a problem with the VMID reference, which is a common "ground" of the audio codec which handles all audio I/O before the CPU.
This should be approximately 1,65 V reference to ground. If you have a multimeter, this can be measured between the battery ground and pin 1 on the rec gain pot.
I'm pretty sure that one or both of the DC-blocking Caps from the Output OP have gone bad. These are C19 & C38 of 22uF, the two slimmer ones slightly to the left of this pic: https://www.instagram.com/p/BY_oUn0nSuF/


I had half a thought to replace those when I had it apart, but I had already taken more time taking it apart than I had expected. Unfortunately I decided against ordering them... I just placed an order, so maybe in a few weekends I can get an update on how that goes. I will absolutely keep this thread updated with the results.
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By DjDiskmachine Thu Jan 24, 2019 7:52 pm
NearTao wrote:Well that was poorly worded on my part. What I probably should have said was the main volume controls the output to the headphones (as expected), but no, it doesn't reduce the noise when sampling from audio. Hopefully that makes more sense.
/


Wow I completely misunderstood you then >_<' So you mean that the gain is set to the max level and not adjustable? In that case, it's not the capacitors but rather the gain pot that's broken.
Without a reference to the common ground shared with the Main Volume strange things will start to happen, but it's hard to say anything for certain without being able to perform measurements. :/
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By NearTao Fri Jan 25, 2019 10:03 pm
Well I replaced C19 & C38 before catching back up on the post... and sadly it didn't do anything to help the line input noise. I'm kind of suspicious of the capacitors that are near the mic/line in button (I think they are 110uf, but I'll check it out later).

As you mentioned, the main out pot may be problematic. After doing the last surgery there is crackling back on the pot when I turn it. I'm out of time at the moment to goof around with it, but I'll probably try and solder the pot again and just see if there is some other goofy connection problem. Otherwise maybe I'll check out MPC Stuff to see if they have a replacement board.

Don't worry... I'll keep poking at this, even if it takes another month or two to find the problem :)
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By DjDiskmachine Wed Jan 30, 2019 10:06 am
NearTao wrote:I'm kind of suspicious of the capacitors that are near the mic/line in button (I think they are 110uf, but I'll check it out later).


Yeah? What do you base your suspicions on? ;D

NearTao wrote:Otherwise maybe I'll check out MPC Stuff to see if they have a replacement board.

I don't think u need to replace the whole board, just replacing the pot should be enough unless the board has some obvious damage.
I'm actually shopping for a replacement pot myself, didn't find one from Swedish retailers that sppears to be 100% compatible tho. :/

NearTao wrote:Don't worry... I'll keep poking at this, even if it takes another month or two to find the problem :)

Good! Keep at it :)
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By NearTao Mon Mar 04, 2019 11:28 pm
Finally graduated with my MBA... so now I have some more free time. Looking at the schematics for mic/line in, I think I'm going to try and replace C203/C204 first and just see if that makes a difference. Since I already replaced C19 and C38, I've already got a few more 22UF 16V caps... so it *should* be something I don't actually need more parts for. I'll probably give it a try in the next day or two and see if it helps any.

EDIT: I just took the system apart and looked at areas that seem to have the potential to be problematic. Actually, I'm a bit more suspicious of the 1uf 50v caps, though I don't think they are part of the line in when the mic button is off. I still think I'm just going to order a pair and replace them while I am in there.
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By DjDiskmachine Thu Mar 07, 2019 8:41 am
Welcome back into the fray!

What do you base your suspicion on? What number are these caps you're talking about?

edit: Funny, I realized we're talking about the C40, 41 that are speced as 1uF 50V in the BOM, but as 1u16V in the schematic.
These are DC blocking caps that go to the line in of the TLV320AIC23B Audio Codec. Seems very unlikely to me that these would cause this problem.
I'd rather investigate the decoupling of the voltage rails that supply this IC with 3.3V.
C105 and C12 stand out to me as especially probable culprits.
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By NearTao Sat Mar 09, 2019 5:14 pm
DjDiskmachine wrote:Welcome back into the fray!

What do you base your suspicion on? What number are these caps you're talking about?

edit: Funny, I realized we're talking about the C40, 41 that are speced as 1uF 50V in the BOM, but as 1u16V in the schematic.
These are DC blocking caps that go to the line in of the TLV320AIC23B Audio Codec. Seems very unlikely to me that these would cause this problem.
I'd rather investigate the decoupling of the voltage rails that supply this IC with 3.3V.
C105 and C12 stand out to me as especially probable culprits.


Well...this continues to be an adventure...

I did replace C40 and C40... and have, as a result... disabled my right channel (whoops).

I thought I had solved the problem though because after hooking everything up to my studio speakers it sounded great. Woohoo... I brought it back upstairs, and guess what... the headphone jack still has the problem... *sooooo* I plugged my headphones into the L output and it sounds crystal clear as well. Apparently I need to fix something in the HPJ circuit.

Guess you were right, I was barking up the wrong tree :)
By Sonar Sun Feb 09, 2020 11:03 pm
I recently bought a used MPC 500 and the noise was pretty bad.

Just to say that I have also had success replacing the caps as above.

I ended up using Nichicon PW series as below, a pack of 10 of each ended up being £3.35 with free delivery from RS:
Nichicon 100μF 16V UPW1C101MED
RS no: 715-2549
Nichicon 220μF 16V dc UPW1C221MPD
RS no: 715-2559
By Sonar Mon Feb 10, 2020 10:03 am
Also a few tips given the linked photos of MPC 500 disassembly have now expired.

I followed the MPC stuff guide to get the case open:
https://www.youtube.com/watch?v=YCa6TmVMaac

Note you don't need to take out the external screws in the center near the battery cover. These appear to secure hold offs that will fall in to the case if removed.

Next use the MPC 500 service manual and follow the first few pages to remove the upper boards. You don't need to remove the display (I did and accidentally snapped a tab!).

The multiway connectors are pretty easy to remove/replace if you need more space, even the delicate looking CF drive connector.

When you get to the main board there is a small black plastic clip that should be gently pulled back. Also around each 1/4” jack the metal tabs actually pull up and out with a pair of needle nose pliers, this will allow the board to be pulled back then up and out.

Only other tip is take photos of disassembly and to leave plenty of room on the capacitor leads as the caps have to lie flat on the board for everything to fit back together.

Hope this helps future readers!