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 Forum index » DIY Hardware and Software
DIY - destroy it yourself
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zipzap



Joined: Nov 22, 2005
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PostPosted: Wed Jun 14, 2006 5:29 am    Post subject: DIY - destroy it yourself Reply with quote  Mark this post and the followings unread

Sorry, this is not really belonging in this forum, besides from being a warning, but i know you people might be able to help me, so i just post this:
I just did something really stupid. My friend gave me his novation bassstation keyboard to take a look inside. It´s sending midi just normal, but doesn´t give a sound anymore. I noticed some slight lfo noise when i turned up resonance and lfo filter mod, so i had the idea that the vca might be getting no gate from the keyboard (silly idea).
Now things get really stupid because the synth has a jack labled ext. controll. Now i know that it´s for some optional hand controller thing. Unfortunately i thought this must be for external cv/gate. So i gave it some 9v from the psu. Really stupid, i know.
Eversince the lights went out and absolutley nothing is working anymore.
All i can mesure is that it now draws about 500ma with 9v pluged in. Pretty much i think since the synth can be run of 6 aa bateries, but i don´t know how much it was before.
Can´t find a shematic anywhere. Maybe novation will help...
If you got some idea what i could do, or what might have happened, please tell me.
Cheers
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Uncle Krunkus
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PostPosted: Wed Jun 14, 2006 7:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Man! Surprised
Nice job! Embarassed
Don't worry, every technician has done something really silly that cost money and/or credibility at some time. It's how you learn what not to do! Smile

I hope local wasn't turned off! (local is the setting which tells the internal sound generators whether they should play what's being hit on the keyboard or only what comes in via midi)
That would explain the midi working but no sound situation.

1. What is the jack supposed to do normally? (when it's not fending off 9V attacks from outer space Laughing )
2. I doubt that you would have taken out the CPU. All external connections should at least gaurd against that.
3. There is a chance you've blown the 5V regulator. (which would explain the completely dead appearance) You need to check the power coming out of the PSU board to work out if it's okay. Be careful if you get anywhere near uninsulated mains connections!!!

You might just want to bite the bullet and send it off for repairs. It might be an expensive lesson, but sometimes it's better to look after the friendship first and nurse your pride later.

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zipzap



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PostPosted: Wed Jun 14, 2006 11:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Uncle Krunkus!
Indeed, thats how you learn!
Local turned off - good idea. Normaly something like this is the solution. Not in this case though.
The jack is intended for an external mudulation controller, i think something like the "guitar" neck some synths have. Don´t know what kind of signal it expects, but sice it´s an analog synth i thought cv/gate.
i can´t see any protection diodes around the chip.
There are two smd ics calld 78l05. 8 pin chips. When i plug in that 9v adaptor they get so hot i just burned my finger.
Looks like you brought me one step closer. the 78l05 can give 100ma at 5v, the synth is drawing 500ma at 9 v. Must be something wrong there.
At 9 v input they both output 1,1v. Guess now i need two new regulators, someone with smd soldering skills, and some luck that nothing else is broken. (which i feer is - the regulators must have died for some reason.
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Uncle Krunkus
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PostPosted: Wed Jun 14, 2006 6:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

No, they may not be dead. I had a situation like this and it turned out that further down the track a bypass cap had gone short circuit. This meant that the 5V was not available for the CPU, and the regulator was getting really hot. Don't leave it turned on for long though or the regulator/s will burn. At this stage it might be okay though.
So, beyond the regulator/s there is some sort of short or partial short. This is where it gets interesting. Smile
Is there some way of isolating the regulators and the next 6 or so components from the main CPU and associated chip feeds? Maybe a link you could temporarily cut? That's a good way of dividing the frustration in half.
If you have a capacitance meter I'd start by pulling caps and checking them. (the 9V may have come down into an electrolytic backwards and shorted it out)
If it starts to look like the short is coming from a chip, then I'd probably let it go to the repair shop.
Keep me posted. Wink

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zipzap



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PostPosted: Thu Jun 15, 2006 1:43 am    Post subject: Reply with quote  Mark this post and the followings unread

I don´t have a meeter, but if a cab is bad i think i can find out. Most of the parts on the board are smd, i don´t want to touch those, but there are a number of normal 100uf elektrolyts around the regulators. i´ll check those. Just noticed that there is a third regulator, a lm317l.
if i measure the resistance between the 78l05s outs and ground (wich is propably bullshit since it´s turned off semiconductors) i get 3 Ohm. Now that sounds like a short.
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Uncle Krunkus
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PostPosted: Thu Jun 15, 2006 2:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah it does,
If you desolder the regulator and it still says 3R (looking across the rest of the circuit, not the reg) then that's why they're getting hot.
You can test a cap for a short with just an ohmmeter. You'll get a short which quickly goes to high resistance if it's okay. A larger cap will take longer, but if it stays low R it's cactus.
I agree about not messing with the SMDs if you haven't got the right tools.
The LM317 is adjustable. You can work out what should be coming out by looking at the values and connection of the surrounding resistors, but I can never remember formulas, you'd have to look it up. Worry about the 5V lines first.

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zipzap



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PostPosted: Fri Jun 16, 2006 5:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Since those regulators are smd i fear to touch them right now.
Spent quite some time looking for a schematic. Novation hasn´t answered yet and i don´t know if they will. In case someone has an idea where to find some service manual/schematic for the bassstation keyboard please tell me. Thanks!
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bugbrand



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PostPosted: Sat Jun 17, 2006 1:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, my two cents is that much of the time now (although the bass-station is slightly older) things are not really designed to be repaired - if something goes then a new board may be used - quicker (thus cheaper) to replace the whole board than search through for the fault - or, with things such as ipods and minidiscs, the whole thing is just chucked (..one of the reasons why the modern world is a little bit stinky..)
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zipzap



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PostPosted: Sat Jun 17, 2006 1:58 am    Post subject: Reply with quote  Mark this post and the followings unread

I just read an article that in many cases it is common with mds and stuff acting strange to replace the thing and just resell the broken unit, just in case someone won´t notice or care...
Well, Novation just informed me in a friendly letter that they are "unable" to offer any schematics. Someone could steel the concept of the saw-osc and the vca.
I still haven´t touched any smd parts, but i have a suspicion.
There is a 74hc147 right next to the jack i attacked. Several of it´s inputs are at ground, but that might be intendet. but there is one out also at ground. It´s either normal for this chip when not powered, or i´ve found my short (or one of them).
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zipzap



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PostPosted: Sun Jun 18, 2006 3:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Meanwhile i touched some of the smds. I disconnected pin16 of the 74147. The short is still on the board. Then pin 1 of the 7805. Still short. Guess i´ll have to continue like that. About 25 ics to go...
Than continue with cabs, resistors and diodes.
Propably till there is only the cpu leaft and i throw everything away..
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zipzap



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PostPosted: Mon Jun 19, 2006 1:51 am    Post subject: Reply with quote  Mark this post and the followings unread

now everything but the cpu is off the 5v líne. The short remains.
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Uncle Krunkus
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PostPosted: Mon Jun 19, 2006 3:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Bugger! Crying or Very sad
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