Diagnosis/Repair Yamaha DD-55 Drum/Midi Machine Advice?

[d3cr3p1t]

I bought this DD-55 drum machine/midi in excellent structural condition from a friend, but he has been using a 500ma 12V instead of the manufacturer rated 1500ma or 1.5A 12V AC adapter.

I tested it with a modular 1.5A 12V power supply in addition to loading the DD-55 with 6x 1.5V "C" Cell (= 9V wth?)batteries and it reacts the same as it does with the underrated PS. When plugged in for the first time and switched from "Standby" to "ON" my 3 digit display flashes half of a random character once for a split second and I hear the speakers getting initial power, but the display and LEDs remains black and I can't trigger any sound or functionality whatsoever, and then when i turn it back to "Standby" I can hear the speakers turn off...

I've inspected the PCB and I really cannot see any evidence of electrical damage, no melted capacitors or oxidation anywhere. I tested the continuity of the 12V input power port which was fine..

So what is next in the chronology of diagnosis? Further multimeter probing? Electrolytic capacitor replacement?

I would appreciate any advice.

[HayZee518]

a larger power supply would supply what the circuit needs to operate. all the wattage means is there's more power available to the circuit and won't cut out after 150 Mw. Check your power path to the unit. first thing the power will come up against is the power supply diodes [four of them] or a bridge rectifier. next is a load resistor, an inductor and electrolytic filter capacitors. there may be a zener diode in the circuit. this locks the ps output to a preset value of the zener. there may be a regulator circuit using an IC.

[d3cr3p1t]

Thank you for the response HayZee, although i'm not sure what you mean about using a larger power supply. Are you suggesting I use higher than a 1.5Amp source? And that it would act like a reservoir, not actually forcing a dangerous load?

I have measured low voltage on what i'm guessing to be a large sound/memory bank or midi IC, I have no idea what it should be getting though so it was really more of a path test. Not sure if that tells you anything..

I think I have identified a voltage regulator on the board, but there is also an internal fuse that I am curious about, because it isn't blown. I was afraid that the unit had been damaged by an electrical surge, but the apparently good fuse is indicative of some other cause?

Any tips for probing? The board is simple enough that testing nearly every component is actually possible, if that is a realistic denominational approach. Assuming I was moving in the correct order.

I've done some very rudimentary electronics work, but its been more borne of financial necessity than technical experience. I apologize if I didn't quite absorb everything you've already suggested.

P~...I was going to upload a couple of shots for reference but I have learned that isn't possible until I post 15 times.

[HayZee518]

Troubleshooting electronic circuits really needs more than just a digital or analog meter. They're good if you have a schematic with voltage point pinouts, but to follow a signal path an oscilloscope is necessary and an audio signal generator. These can run into big bucks. In reference to your power supply question, smaller is not better. While it may work like the 500 ma supply specs call for a 1500 ma supply. Bigger would be better. Reason is as you turn up the output the current draw through the amplifier circuits goes up. If that power isn't there then you'll under drive the circuit and can cause overheating, pops and squeals.

[d3cr3p1t]

I've spent the last two hours swimming though gibberish online trying to find a schematic for this thing and I can't even find one to pay for. Let entirely alone getting one free.

I'm not exactly sure what the stipulations for using copy protected circuit schematics are, but Yamaha has officially discontinued this product and will not service it.

Any recommendations for purchasing or procuring a legal copy?

And thank you again for your time and valuable suggestions, HayZee.

[HayZee518]

look into the Howard Sams site for a schematic. They'll sell you a bunch of schematics for other units but yours will be in the same packet. They've been selling schematics for the past 60 years on every product made.

[d3cr3p1t]

It appears the only modern product in the world that Howard Sams doesn't have listed online is the Yamaha DD-55.. They say they can get everything in 48 hours.

I found what looks like a defective or overloaded transistor? Found it in a frustrated search today with my LED/magnifier...
(I can't link either?)
h-ttp://i16.photobucket.com/albums/b11/VioLenTsobRieTy/CIMG1144.jpg

That transistor was split all the way along the seam.

I pulled it back a bit to see if there was damage..
h-ttp://i16.photobucket.com/albums/b11/VioLenTsobRieTy/CIMG1147.jpg

Looks toast to me.

I've got some sort of ID but I haven't been able to find anything online to determine its specs. Any ideas? Here is the ID:
h-ttp://i16.photobucket.com/albums/b11/VioLenTsobRieTy/CIMG1145.jpg

But do the symptoms lend itself to this result? Will there have been any repercussions elsewhere?

[HayZee518]

I went through 34 pages of web sites on the dd55 with little information. One site listed all yamaha equipment and yours was not found in there. I did find the yamaha address:
YAMAHA CORPORATION OF AMERICA
Electronic Service Division
6600 Orangethorpe Avenue
Buena Park, California

[d3cr3p1t]

I received this email from Sams today..

-----------------------------------------------------------------
Customer Care
6:53 AM (5 hours ago)


Sorry we checked other places and could not find anything on this.


----
Jeff Morris

SAMS Technical Publishing, LLC
9850 East 30th Street
Indianapolis, IN 46229

Phone: 1-800-428-7267
Fax: 1-800-552-3910
Email: customercare1@samswebsite.com
----
-----------------------------------------------------------------


So... there really isn't ANY technical information on this product anywhere.
well damnit, what a disappointment, but i've at least got one obvious thing to try; replacing that transistor. I'd really like to keep this thing out of the landfill..

And again, thanks very much for all the help HayZee, wouldn't have made it this far without all the advice

[adnadeau]

Ic930

Your last photo shows the component in a spot marked on the PWB as IC930, so it's an Integrated Circuit. A Google search of the S812 marking on the component shows it as a Seico voltage regulator. (OpenDNS dot ic-on-line dot cn/IOL/datasheet/S-81240_327305.pdf). The 50SG on the next line indicates 5.0V output. If it's split in half, it's FUBAR. Its failure may have been due to the undersized power adapter or anything else. Electrolytic capacitors frequently fail; look for a bulge in the top of the can or a pushed-out black rubber seal where the leads go into the PWB. You can visually follow the printed circuit paths to see what's upstream and downstream of this component. You should be able to get a replacement part on-line from Allied or any other electronic supplier.

[d3cr3p1t]

Brilliant, thank you adnadeau for the insight. Looks like $1.99 for the regulator, and $7.99 for shipping

I'll post my results upon replacement.

[d3cr3p1t]

After being hastily reassured by a yamaha "Technician" that I would solve the problem by replacing my split IC 5v regulator (which cost me $10), the problem has apparently worsened.

My display has stopped emitting any light at all, where with the split regulator it would flicker once when plugged in then nothing. I can hear my speakers now turning on more clearly, I think, which is odd paired with loss of display. I was sure to mount the new regulator (identical) the same direction as the original, used 62/36/2 Rosin core .022"D solder with a 25w iron and certainly didn't burn the board or any pathways. Inspected for shorting, those pins are close together but they didn't join anywhere.

Discouraging.
But as I was tacking it in, I noticed some sort of residue forming around my solder on the board, I assumed it was flux or something from the factory that was just heating up and becoming visible, but maybe rosin? And if that were the case would I be shorting to my other pins? Rosin is conductive, isn't it?

[HayZee518]

rosin is not conductive.

[adnadeau]

You can wash off the flux with rubbing (isopropyl) alcohol and a cotton swab or toothbrush, but I just usually leave it there.

Looks like the regulator failure was the result of something else downstream shorting out. Now that it's working, the original problem is dragging the whole power supply (on the PWB) down, which may be causing the display problem. Stick your finger on the regulator and see if it's really getting hot. If so, search for some other component that seems too hot. How many other active components need that 5 Volts? Any filter caps that appear bulged? See if you can sketch out a schematic.