www.megadrum.info

Hi,

a few days ago my MD started to behave strangely. Some (not all) parameters won't load on startup. First I thought I forgot to save my changes, but later I discovered that this was not the case. Otherwise the unit works fine, so once the parameters get set, they become effective for that session. On the next power up they may or may not be retained, or some others may change.

It looks like a hardware issue. It's a synthex v3.1 board. Where shall I start the investigation?

Thanks,

Endre

el-dr wrote:Hi,

a few days ago my MD started to behave strangely. Some (not all) parameters won't load on startup. First I thought I forgot to save my changes, but later I discovered that this was not the case. Otherwise the unit works fine, so once the parameters get set, they become effective for that session. On the next power up they may or may not be retained, or some others may change.

It looks like a hardware issue. It's a synthex v3.1 board. Where shall I start the investigation?

LCD contrast, number of inputs are loaded on boot regardless of all other settings. Are they retained when other settings are reset to default? (I understand by "not retained" you mean values are reset to default)

If it is a hardware problem than the only solution is to replace Atmega but I have not seen any Atmega failing.

If it is a firmware bug I need to reproduce it to be able to fix it.

dmitri wrote:LCD contrast, number of inputs are loaded on boot regardless of all other settings. Are they retained when other settings are reset to default?

The LCD contrast is always correct, but I think I've seen the no. of inputs reverting to 18 occasionally.

dmitri wrote: (I understand by "not retained" you mean values are reset to default)

That's right.

dmitri wrote:If it is a firmware bug I need to reproduce it to be able to fix it.

I don't think so, because I'm sure that others would have reported it as well.

I also updated to the latest fw and another strange thing happened after completion: when I stored a config, I didn't get the usual "Done" message, but the display reverted straight to the config number. First I thought you removed that message for some reason, but then it reappeared after a few reboots. I'm totally overwhelmed by other works, so I had no time to swap the Atmega between my rack MD and the Zendrum-style fingerdrum to check for differences. This is looking weird...

I have a suspicion you might have some bad soldering somewhere on the board or a loose break/short which might be causing the intermittent problem.

dmitri wrote:I have a suspicion you might have some bad soldering somewhere on the board or a loose break/short which might be causing the intermittent problem.

I was afraid of getting this answer. Can you recommend some areas on the board that needn't be checked?

el-dr wrote:

dmitri wrote:I have a suspicion you might have some bad soldering somewhere on the board or a loose break/short which might be causing the intermittent problem.

I was afraid of getting this answer. Can you recommend some areas on the board that needn't be checked?

I suspect you won't like my answer again:) It could be almost anything - power cables/tracks, bad capacitors, buttons cables/connectors, Atmega's socket.

dmitri wrote:I suspect you won't like my answer again:)

Very true:( It wouldn't be a big deal to resolder everything, but it sounds like a nightmare to spot a shaky component... but at least I have a spare set to keep things running while at it.

I replaced the PCB, but the problem was still present... The only common components between the two systems were the LCD, the pushbuttons, the encoders, an external PSU (switched off when drawing power from USB). I don't think any of these could cause such an issue. Then I tried one thing: I powered up using the external PSU and then connected via USB (this is how I used MD in the past) and the problem hasn't occurred since then, so it seems it's something to do with the USB bus power. Can you confirm that it potentially can cause such a problem?

One more question: I couldn't remember if the spare board had the latest USB fw installed. How can I tell if it has it or not?

el-dr wrote:Can you confirm that it potentially can cause such a problem?

Bad power can cause all sorts of problems.

One more question: I couldn't remember if the spare board had the latest USB fw installed. How can I tell if it has it or not?

Look the updates dates in viewtopic.php?f=3&t=702 and correlate it with the date I sent you the kit.