M-Audio Venom repair

[Jose EB5AGV]

Well, I can't resist when I see a cheap, not working synth... Last week I saw an M-Audio Venom, in apparently good shape, sold as "only MIDI controller, unknown fault". It was 75€, shipped, so I pulled the trigger.

 

It arrived yesterday but won't have time to even open the box until tomorrow. But I couldn't resist to open this thread, just in cause someone has gone already this way 😅

 

More to come!

 

Jose

[Doerfler]

Best to you on this project. The Venom, as it's name suggests, has a very aggressive sound, should you get it to work

[Jose EB5AGV]

Well, I have finally opened the box... and here you have the first pictures of it.

 

At least it powers up:

 

 

Venom... good name!

 

 

Once you remove a ton of screws and the keybed connector...

 

 

Once the keybed is removed, you have the electronics attached to the top cover:

 

 

And on this board should be the problem. I have already checked all capacitors but, sadly, they are OK, so it won't be a simple fix:

 

 

The unit generates a faint sound, barely audible at maximum output and monitor levels, which is promissing.

 

Next steps are to check internal voltages (it seems to be a switched power supply on that board), follow the signal from LINE OUTS to the D/A, and try to find the fault on that path.

 

There seems to be no schematics available. I will try to contact M-AUDIO, but don't have high hopes.

 

All in all, another interesting project ahead!

 

Jose

[Jose EB5AGV]

Well, it seems my guess was not far from the truth!. I have checked and there is a switching regulator which gets burning hot and there is no proper positive nor negative output voltages from it (is a dual voltage regulator). It is marked LBHM and corresponds to a LT3471. So a replacement has been ordered. More to come!

 

[Threadslayer]

It looks like there has been some rework done to this board already - or else it was hand assembled - which is unlikely I would think. Definitely some scorch marks and questionable solder joints around U99, C476, L1, L2, C85 and L4 for example. So there may be some surprises downstream from the switcher also.

Have fun. 😉

 

[Jose EB5AGV]

2 minutes ago, Threadslayer said:

It looks like there has been some rework done to this board already - or else it was hand assembled - which is unlikely I would think. Definitely some scorch marks and questionable solder joints around U99, C476, L1, L2, C85 and L4 for example. So there may be some surprises downstream from the switcher also.

Have fun. 😉

 

 

It seems more like a reworked board after production (*). The unit seemed unopened, and I am very used to find small details which show an electronics item has been tampered with (as tiny marks on screws, displaced wiring, pen marks, cabling or connectors dents, ...). So maybe the PCB production was of questionable quality to begin with. 

 

As the unit seems to work, except for the audio output (which without the +/- analog power supplies is expected), I am moderately confident it will work once the switcher is replaced. Let's see!

 

Jose

 

(*) Back when I worked on a company which manufactured electronics, there was a full line of workers who just checked new manufactured circuits, fresh from the automated production lines, and reworked any suspicious solder point. That is what could have happened here, IMO

[YashN]

It would have been much cleaner work if it was a factory rework IMO.

[Jose EB5AGV]

38 minutes ago, YashN said:

It would have been much cleaner work if it was a factory rework IMO.

 

Well, note that the image is zoomed. And also, if you look in same detail to the big ICs soldering, the quality is not very good. I would think that chinese PCB manufacturer is not that great (as, as you can imagine, this unit is Made in China)

 

All in all, the synth seems good enough to be fixed. Let's see what happens when the +/- analog supply voltages are back! 😁

[Jose EB5AGV]

Well, the switcher IC arrived yesterday and I installed it. Not a nice experience due to the soldering... It is a very tiny IC (about 5x5mm), with no pins on it, and a big ground area which makes soldering harder:

 

 

 

This is the bad one:

 

 

Kapton tape used to protect adjacent components:

 

 

After some soldering and cleaning work (there are two pins joined by a trace on the PCB, is not a fault), here you have the new IC placed:

 

 

Then the test, using a lab power supply, set at 9V 0.5A maximum... And the switcher generated positive and negative voltages, but not the right ones 🤯. It seemed like a problem on the ICs powered by this power supply. And, finally, I found there was a failure in one of the connections of the replaced IC and so the positive output had gone too high... And no less than 5 double opams had died (luckily, all same type). Oh well... I removed them, soldered another switcher IC (as it was just impossible to get the soldering right), and now I have +9 and -9Vdc 🥳

 

One of the damaged opamps:

 

 

Now I am waiting for the replacement opamps to arrive. Let's hope once replaced (will do it one by one and recheck voltages carefully each time) the Venom will finally generate some noise! 😅

[Doerfler]

you have the patience of a saint 

[Jose EB5AGV]

Well, things are not easy with the Venom!

 

After the apparently good test of +/- 9Vdc generation (without any load), when I got from Mouser the replacement OPAMPS, just installing one on the PCB made the switcher go nuts. So the OPAMPS were not the root cause!. Oh well...

 

I had to replace again the switcher IC, as even with limited current from the lab power supply (set to 9V/0.5A), it failed while trying to find the problem. Also, I was not sure about that switcher IC being not a counterfeit, as the labelling was almost invisible after cleaning, and the surface was rough. So I ordered legit ones from Farnell and did, again, the replacement work (note: they are 3x3mm, I wrote before 5x5mm)

 

These are the good ones:

 

 

Here you have it replaced... the small added wire is because one trace was damaged and this wire bridges the missing connection, luckily the same than the adjacent one:

 

 

It seemed to be better, but still with just an OPAMP installed, the negative voltage (-VA) decreased from -9Vdc to about -4Vdc and the IC got pretty hot.

 

I found the service manual for the Venom online and traced on the schematics all and every point the -VA voltage was present. I discarded all and every componet (capacitors, diodes) on the circuit. All were fine!. SO I removed the only OPAMP on the circuit... and -VA was fine again 😳

 

Then... what if the switcher circuit had a problem?. I checked the coils and, BINGO!, one of them, L2, was shorted. Oh my!. That explained while, under any load, the switching of a basicalle short load, got the switcher transistor for that rail pretty hot. Basic electronics 🤣!

 

Now, well, such a miniature SMD 10uH/0.49A coil was sure not on stock on my lab... But, well, I was not going to wait for another components order, so I built them with some suitable toroids. I selected the T37-43 ones, as 5 turns would be enough to reach 10uH, according to an online calculator.

 

Here you have the contraption, first measured and then installed (I replaced also the adjacent coil, as it seemed also slightly damaged):

 

 

 

Now the test!. FIrst +VA

 

 

Then -VA

 

 

At long last!. I added the other four OPAMS and it kept working.

 

I added some glue to keep the coils on place:

 

 

And this is the overall view of the finished board:

 

 

More to come soon!

 

Jose

[Jose EB5AGV]

Here you have a video of the Venom, still partially disassembled, playing its DEMO song. What a great moment for me, after all the work!

 

 

This is not the end of the work, as I found that there was a key which didn't work... and it was not only a cleaning contact case.

 

I am working on it and will post the results of my keyboard repair soon!

[YashN]

Great progress. The key should be an easy fix compared to what you already did.

[Jose EB5AGV]

Sorry, yesterday I published my video on my other YT channel and it was intended to be on this one. I put it again as I will remove it on the first one:

 

 

[YashN]

Good job. Everything works? How do you like the sounds?

[Jose EB5AGV]

43 minutes ago, YashN said:

Good job. Everything works? How do you like the sounds?

 

Well, there has been some more work after that video, as the key which didn't work had some serious problem, because the carbon contact had been damaged by some liquid (which, I suspect, could have something to do also with the main problem)

 

Here you have what I found, after careful cleaning the contact. The missing sections were attached to the rubber contact...

 

 

For comparison, this is a good one:

 

 

I used a product called Wire Glue, which is based on carbon and, when it hardens, the adherence to the PCB is very good and the electrical resistance very low. I did my best to duplicate the original shape 😬

 

 

After it cured (I left it for about 6 hours), I put back the (also cleaned) rubber contacts. It is useful to use an small screwdriver to put back the rubber assembly support points:

 

 

After that, the Venom keybed worked flawlessly 🥳

 

Now, about the sounds, well, it is kind of harsh 😆. I have found some patches online which I would like to check. I have installed the USB driver and the editor software and, even being old, it works on a Windows 10 PC. Next step is to upload some patches to the Venom

[YashN]

Some of the PCB traces may be corroding too. Otherwise, nice work.

[Jose EB5AGV]

7 hours ago, YashN said:

Some of the PCB traces may be corroding too. Otherwise, nice work.

 

Yes, they are darkened, but electrically sound. Who knows what liquid entered the unit. Judging by the residue I removed, maybe some coffee or soft drink

[My Keys And Me Are Vintage]

Great job with the troubleshooting and repair! I am not sure I would have gone in for more repairs on that particular keyboard, but I respect the determination! I have never tried Wire Glue, but I am now adding a bottle to my shopping list. 

I really liked how you made your own inductors!  

[Jose EB5AGV]

14 minutes ago, My Keys And Me Are Vintage said:

Great job with the troubleshooting and repair! I am not sure I would have gone in for more repairs on that particular keyboard, but I respect the determination! I have never tried Wire Glue, but I am now adding a bottle to my shopping list. 

I really liked how you made your own inductors!  

 

Yes, you are right. In no way a Venom is objectively worth the time and expenses I have invested on it. But, as it happened years ago, when I did my first amateur radio equipment repairs, they were not cost effective but were great tools to learn. Then, after some dozen repairs of my own gear (I expressely bought not working units), I began to offer my repair services and, 30+ years later, it is my main work (since 2012 I work at my home lab)

 

In the same fashion, when I began with my first synth, a Yamaha SY77 in February 2018, I bought a faulty unit, needed of lots of care. So that was the beginning of my synth repair adventure. By now, I mostly fix synths and audio gear for myself. But have already done some work for other people. My plan is to keep learning on this kind of gear and, step by step, displace some of my repair work to this area. As I enjoy playing keys, it would be like a golden retirement for me 😅 (I will be 56 in a couple weeks, so it is not that far! 🤣)

 

All in all, I enjoy technical challenges, so this has been a good one 👍🏻