[SOLVED] E-Drum Brain Repair - Page 1
Forum section: electronics / repair

author: Richard1972
author_rank: Contributor
timestamp: January 08, 2020, 12:04:10 am
content: Hello everyone, I hope this is the right forum to ask this. I am hoping to get some advice on where to begin trying to repair an electronic drum brain. The board in the picture comes from a session pro DD505 that has a faulty kick drum as the sound is low and muffled, so it barely comes through.To try and resolve so far I have checked cables, assigned the drum sound to a working tom drum, which worked fine. I have changed the sensitivity and the volume of the pad, tried to change the voice to a different sound. I have also soldered on a new female 6.35mm jack connector in case there was a problem with that, but it has made no difference. As my knowledge of such things is very basic, I am clutching at straws really. I don't know how to find a data sheet or schematic for this board so really I am at a loss as to what to do next. Any advice would be much appreciated as I am just stating to learn about these things.Thanks in advance.

author: Mr. Scram
author_rank: Super Contributor
timestamp: January 08, 2020, 01:46:55 am
content: Do all the capacitors look okay? No bulging or leaks?

author: Richard1972
author_rank: Contributor
timestamp: January 08, 2020, 09:35:37 am
content: Thank you for replying Mr Scram. I have looked closely at them and I haven't noticed any bulging or leaks.

author: Zucca
author_rank: Unknown
timestamp: January 08, 2020, 10:02:27 am
content: Quote from: Richard1972 on January 08, 2020, 12:04:10 amSo you change the kick drum sound to a tom drum and it worked fine?What about to chage the tom sound to the kick drum?

author: Richard1972
author_rank: Contributor
timestamp: January 08, 2020, 10:05:44 pm
content: I am able to assign drum sounds to any of the drums or cymbals so long as I am not using the actual jack connector that is used for the kick. Every other Jack seems to be able to work and produce any of the sounds / voices. I took off the female connector and changed it to a new one just in case that was the problem. It didn't make any difference. I plugged the actual kick drum into the other connectors and it worked so I know the drum isn't the problem.

author: Richard1972
author_rank: Contributor
timestamp: January 08, 2020, 10:24:35 pm
content: I have included some more images here to see if this helps. I should add that the image where the jack is inserted into the kick drum connector was taken before I soldered it properly so I know that the crap soldering in the image is not the issue.

author: LateLesley
author_rank: Frequent Contributor
timestamp: January 08, 2020, 10:25:21 pm
content: Just a silly question, have you checked the volume setting of the particular drum sound? You can assign individual volume settings to each drum sound. See "adjust the volume of pad", page 11 of the manual.https://www.kirstein.de/docs/manuals/xd-dd505-en-0110.pdf

author: james_s
author_rank: Super Contributor
timestamp: January 08, 2020, 10:27:48 pm
content: Your description sounds like a hardware fault on one of the physical channels. I would trace the output jack back to whatever drives it, there is probably an op amp. There may also be analog switch ICs for routing the signals, these tend to be fragile.

author: Richard1972
author_rank: Contributor
timestamp: January 08, 2020, 10:29:36 pm
content: LateLesley its not a silly question at al thank youl. I have checked it several times so I know thats not the issue.

author: Richard1972
author_rank: Contributor
timestamp: January 08, 2020, 10:31:35 pm
content: Thank you. Someone messaged me earlier and mentioned the same thing. I will have a look at what you are suggesting, but I don't know how to test that ?

author: LateLesley
author_rank: Frequent Contributor
timestamp: January 08, 2020, 10:52:47 pm
content: I would tend to agree, that it might be an op amp issue, if its not a setting issue. Do you see those 4 8 pin ICs at the right hand side of the board? To me, they kinda look like they may be dual op amps, each chip doing signal detection/conditioning of the incoming signal from the e-drums. If you can trace which one the kick drum input comes to, and then measure around that chip, you could maybe see if it has any off voltages, compared to the others. Each of those chips look kinda mirrored, so 8 channels with one input on each side of the chips. I'd test the diodes and zeners, then measure the input and output voltages on each op amp, just to see if the suspect one stands out as different.Edit : And here's a gem from Mr Carlson, showing testing an op amp with a curve tracer.https://youtu.be/l8ndPgGNKg8?t=1721

author: Richard1972
author_rank: Contributor
timestamp: January 09, 2020, 12:35:14 pm
content: Thank you for that link as the video was very helpful. I have done pc repairs for years, but this has been mainly soldering jacks and that kind of thing. I am trying to teach myself more about electronics and have invested in some equipment to help with this such as oscilloscope, stereo microscope, decent soldering station and other things. In a way I am using this issue with the drum to develop my own skills so I am very grateful for everyone’s input.I am assuming if it does turn out to be the op amp then I might be able to replace it. I still have a lot to learn so appreciate everybody’s help with this.

author: Zucca
author_rank: Unknown
timestamp: January 09, 2020, 01:10:33 pm
content: With an scope you could see then the signal is not moving forward in the circuit board.100Mhz Bandwidth is plenty in 99% of common real life problems.

author: Richard1972
author_rank: Contributor
timestamp: January 10, 2020, 05:51:55 pm
content: I know this is probably a dumb question, but in the link you sent me, has he got his on a breadboard for the purpose of teaching us or do I have to remove the op amps to test them? The ones on this board have 358 on then with EZ723 underneath that..

author: Richard1972
author_rank: Contributor
timestamp: January 10, 2020, 06:45:36 pm
content: Thank you so much for that. I will do it later this evening.

author: james_s
author_rank: Super Contributor
timestamp: January 11, 2020, 01:18:18 am
content: 358 is probably a LM358, that's a very common op-amp that has been around a long time.What I would probably do is trace the circuit back from the affected output and see which IC(s) it passes through, then use an oscilloscope to look at the signal at various points until you find where it changes suddenly, if it's distorted you probably have something like the top or bottom half of the waveform is getting clipped by a bad output. It sounds like you have multiple similar or identical circuits so you should be able to compare similar nodes between the bad one and one of the working ones.If you don't have an oscilloscope you can use a test amplifier. This can be any small audio amplifier, a set of powered computer speakers, a portable stereo with an aux input or one of the many cheap audio amp modules you can get for a few dollars or less from China. Make a probe out of some wire with a resistor of maybe a few hundred ohms to a few k to protect the amp in case you accidentally probe a power rail or something and then start poking around, you should be able to trace the audio all the way from the output back to the source.

author: Richard1972
author_rank: Contributor
timestamp: January 11, 2020, 03:17:08 pm
content: I would like to thank everyone who took the time to help on here. I learnt a lot through this especially about how op amps work and how to test them. I am embarrassed to say however that I have found out that the problem was with my headset and not the drum module. The problem started when I put in my new headset and the sound was not too good with the kick drum disappearing completely. To rule out the headset I tried a different set belonging to my son and another pair he uses in his xbox. Unfortunately I had no idea that a headset with a mic would not work properly. My understanding now is that I need a 4 pin to 3 pin splitter. I was so focused on the module being the problem that never considered that. Anyway, hanging my head in shame, all I can say is thanks again. Your input is much appreciated.

author: LateLesley
author_rank: Frequent Contributor
timestamp: January 11, 2020, 04:52:11 pm
content: There's no shame in finding what the issue was, and a way to rectify it. And you have shared a nugget of information for people to check, before they break into the electronics. We all are learning, and all start with little to no knowledge.So Thank you for sharing what the issue was. We all get days where the experienced engineer can feel like a rookie. :-)

author: Richard1972
author_rank: Contributor
timestamp: January 12, 2020, 11:13:13 pm
content: Thank you. I just felt a a bit of a fool, especially with other people putting a bit of time in to help. Still you are right if anyone else has this issue they might stumble across this and learn from my mistakes. Thanks again to everyone.

author: Mr. Scram
author_rank: Super Contributor
timestamp: January 30, 2020, 02:56:15 pm
content: Quote from: Richard1972 on January 11, 2020, 03:17:08 pmIt's all part of troubleshooting. Anyone claiming it never happened to them hasn't really tried. The important part is that you tried to learn about things you didn't know and kept going until you figured it out. That's the correct attitude and how experts became experts.