Roland KC-110 or AC-33

[dmeek]

I have a KC-110 with a power supply problem. This is a battery powered amp with a multi voltage
power supply, all SMD. A schematic would make it easy. The same board is used in the AC-33.
Anyone have a schematic?

Doug

[nickb]

Can't help with a schematic but I would not be surprised to find a single chip boost converter in there. Look for smallish power inductor and it'll be right next to that. The supply voltage will be present on one side of the inductor. You can then look up the data sheet for the chip check the voltages and signal on the pins.

[dmeek]

The converter is a BD9851, a dual channel unit. The datasheet example schematic shows each channel driving a
single mosfet and inductor but this looks different. The mosfet if that's what it is has 5 pins-maybe a dual unit.
I haven't found a number for it yet. the marking is:

YE
1
K2

Here is a photo. I'm not going to spend too much time on this. Without a schematic it's probably not worth it.
The blown fuse F2 which I've removed supplies power to the BD9851. All op-amps have +15V but not -15V
It's all a little confusing.

http://music-electronics-forum.com/a...1&d=1506885126

[nickb]

It looks like one P-chan and one n-chan FET. I looked in my 2007 SMD codebook but it's not listed. My bet is on the p-chan one being bad. You can figure out which pin is which by bussing out the connection from the FET pins to the BD9851 - or just look for short across it. I have seen the inductors go in these cases too.

[dmeek]

My guess is the BD9851 generates +5V and +3.3V. Both 5-pin parts have the same marking and C224, C223 have negative grounded.
It's a mystery where the missing -15V comes from.

I have the 2014 Turuta SMD book which is very good usually, but not for this part.

[nickb]

Oh... It looked like one is 1K2 and the was 1M2 from the piccie. If they are both p-channel then the chip would be in step-up/step-down mode. That seems unlikely as in that case where does the -15V come from? You could also check for a short on the -15V rail and for a short in the FETs.

[dmeek]

Here's a very good Russian SMD cross reference. Still no luck.

http://chip.tomsk.ru/chip/ChipDoc.nsf/chDigitIndex

[doctor]

These components are the QS5U27 - P-channel MOSFET with Schottky diode.

[nickb]

Doug - I have street cube on the bench. It has the same switcher chip and is used for the +1.5 and +3.3V rails. The battery is 9V and is regulated to 8V for the opamps, there is no -ve supply. The twin power amps are fed from a pair of +5V linear LDO regulators.

[dmeek]

I decided to cut my losses on this one and sent it back. I'm sure I'll see another someday. I fixed a Street Cube a while back.
I was measuring about +1V on pin 4 of all op-amps. This usually tells me that a 7915 regulator is bad though not sure in this case.
I had a dead short on both CPU power power rails (across the 100mf caps) even after removing both mosfet/diode parts.
Too much SMD for me without a schematic. Too hard to trace

btw: The power amp is the square chip in the photo - 20W per channel stereo. Yikes!

[paleeman]

I've read your post a bit too late. I have the KC-110 schematic.

[The Dude]

I've read your post a bit too late. I have the KC-110 schematic.

If you could post it here anyway, it might save someone some trouble in the future.

[g1]

I'm not sure he's allowed to post it, so you may have to send a PM.

[J M Fahey]

I had a small battery powered Roland Cube on my bench some 10 days ago but it was not an electronics problem: owner´s very cute 2 y.o. Son had filled speaker cone of holes pushing a pencil through each and every hole through the chrome plated perforated metal grill.
All SMD but I noticed a 3.3V labelled bus on the PCB, which I assume is for some kind of microprocessor and a 1.5V or so whose use I ignore.

If the amp had had any kind of PCB problem, besides perhaps some intuitive supply one, I would have sent it back or absolute worst replace guts with some of mine.
No Factory support at all here, I can get some schematics thanks to Forum members generosity who post what they have, but ZERO original parts, so what´s not generic and can be bought over the counter, forget it.
Oh well.

Oh, the speaker? no big deal for me, since I repair and build them so am fully equipped for that.

[paleeman]

If you could post it here anyway, it might save someone some trouble in the future.

Hi Dude

I most certainly, can. But I rather choose e-mailing, if somebody needs it, than posting it. Reasons: 1. The file size is larger than 10mb 2. What g1 said