I bought a broken SR-16 drum machine and need help finding the no sound problem

[gica69]

So, this is an SR-16 4 midi channel small drum machine I bought for my daughter to play along on her guitar. I only get a hissing sound out of any of the channels. I tested most of the components and have not figured it out yet. I am including a picture of the board. A bunch of the resistors have one end that shows continuity to ground, and one small capacitor has continuity to ground on both legs. The cap is good when taken out.
I noticed that when I unplug the power jack a lot of components do get shorted to ground sort of speak. When I plug it back the continuity disappears. I took out the jack and it seems to be built this way. It connects to a push switch.
Watching a repair video on Youtube which is the only one available, guy is great at solving his problem. I got some voltages but not too much.
#21 - Alesis SR-16 drum machine repair - YouTube
In the picture the 4 channels have a ground and 4.4V on the the other contact.

The one capacitor shown bottom left shows short between prongs. All the resistors circled are short to ground where circled.
I am looking for advice on what to do next. Thanks in advance.

 

[gica69]

OK as you know this was bought like this and upon reading a little more online, I just now realized that the sucker takes a 9V Ac adapter and it was sold to me with a 12V DC adapter. So before I do anything else I have to get an AC adapter. Cannot believe it.

 

[Martaine2005]

Without getting my opinion blown to pieces, in some cases you can use a DC supply for AC powered equipment.
Get the proper adapter first and then go from there.

Martin

 

[gica69]

Yeah, but not in this case. I have 100 different adapters, and I found some AC ones among the many DC ones. 2 of them 9V that measure 10.5 when tested. So, the machine came to life. I cannot believe it. My wife says to me I wouldn't have checked for AC adaptability but expected you to. I left the room of course cursing knowing she was right. Well at least I got to measure every component 3 times. Got to read data sheets on several chips. And got all different wrong measurements for it all. It only took me 3 days. I also bought some nice soldering wire from Amazon, mine was getting old and I had really thin one at .015in or thick one at 2.5mm. So, I bought some 1mm by Austor 60/40 and it melts like butter, flows nice too. Well, this took a turn for the unexpected. I thought I was gonna learn something here.
I am glad the DC didn't cause any problems, being 12V and all.

 

[Harald Kapp]

I am glad the DC didn't cause any problems, being 12V and all.

9 V AC is RMS. Peak is 9 V × sqrt(2) = 12.7 V peak. After the rectifier and filter capacitor the internal DC supply from the rectified AC will be ~ 11 V. So it was to be expected that 12 V DC would not damage the circuit.

AC may be needed to generate an internal negative supply voltage for the analog circuit, who knows? That may be the reason why a DC adapter didn't work.

Btw: How old is the unit? You may want to swap the battery (CR2032?) for a new one while you have the case open. This battery is there to save data in a nonvolatile RAM (battery backed-up SRAM). When it gets drained, the unit will "forget" settings during power off. Probably not a big issue, but easy to remedy with a new battery.

 

[gica69]

Yeh that's exactly what the AC did it provided the negatives for the analog system on the chip I removed. Prior to that I had no negative readings. But I know one thing from now on first thing I will do is check the AC adapter make sure it's the right rating. I actually found 2 of the 9V adapters but the plugs were not fitting in the jack so had to cut wires and I found a plug that worked. Saved 20 bucks
The unit is from1990.The battery tests at 2.7V It doesn't just slide out either. I probably have to desolder something.

 

[Harald Kapp]

The unit is from1990.The battery tests at 2.7V

The battery voltage may drop to a lower value when the battery is being used. A CR-2032/HFN could be a suitable replacement.
But you don't have to swap the battery as long ass the unit works satisfactorily.