Author Topic: Switch Mode Power Supply  (Read 1444 times)

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Offline bob225

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Switch Mode Power Supply
« on: April 13, 2018, 05:16:20 pm »
Hi All

I recently picked up a new Project a Roland RD-150 circa. 2002, The main control board was smashed to bits what i have now rebuilt after many hours and swearing at it

Now The SMPS is playing up with a nasty buzz and crackle - initially it was putting out a low voltage (under load) what was cured by a re-cap

Roland have discontinued support for this model 8-10 years ago so spares are non existent, I do have the service notes but the SMPS is a Daughterboard and is not covered, i cant even get the specs

Part numbers on the pcb

KPC1694V-0
B104
F8044PA

Part numbers From the service notes

SWPS1
A1DU2L3B104

02127512 (Roland)

Input 100-240v
Output +15, -15, A GND, D GND and +5v

As far as i can tell the DC to DC transformer is a - EEL19-H, Dual primary, Dual secondary (5v and a -15, 0v, +15  centre tapped) I can't find a off the shelf replacement from any UK or US supplier


Any help appreciated
« Last Edit: April 13, 2018, 05:20:14 pm by bob225 »
 

Online tautech

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Re: Switch Mode Power Supply
« Reply #1 on: April 13, 2018, 09:28:25 pm »
Like many SMPS the design most likely closely follows the controller IC's datasheet 'typical application' schematic.
Identify the controller IC and get the datasheet is the first step. If more than one datasheet is available get them all and hunt for a schematic that closely resembles the SMPS you have.

So what symptoms is the SMPS exhibiting now ?
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Offline coromonadalix

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Re: Switch Mode Power Supply
« Reply #2 on: April 14, 2018, 03:32:53 am »
A1DU2L3B104 seems to give some results, but no schematics found, it seems an self oscillating smps ..  sold as an unit only as you said,  but findig it seems impossible ????   

you could find some compatible physical size maybe from meanwell NET-35C series ??  avoid cheap china knock off
 

Offline bob225

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Re: Switch Mode Power Supply
« Reply #3 on: April 14, 2018, 10:20:00 am »
Thanks for the replies

I have been drawing a blank on all the searches, There is no IC on the board just a P4NK60ZFP and feedback on the 5v side

If it comes to it will design a board but I'm a bit rusty and out of touch with modern dc-dc convertors


Edit. Symptoms - Intermittent buzz Like a bee in a coke can lol and the odd ping emanating from the transformer
« Last Edit: April 14, 2018, 10:29:32 am by bob225 »
 

Offline SeanB

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Re: Switch Mode Power Supply
« Reply #4 on: April 14, 2018, 01:24:59 pm »
First, clean off the flux residue from the board, and then resolder all the joints of the capacitors, the switching transistor and the transformer and the secondary side diodes. The main primary side capacitor looks like it is dry jointed, though that could be lead free solder, but resolder it anyway. Resolder Th1 and the 2 jumper wires as well, the ring around the solder joins looks suspicious.

the 2 270k SMD resistors are the start up circuit for the self oscillating power supply, check they have not drifted high in value ( you can check in circuit with no power applied using a DMM, they should measure around 270k or slightly lower, more than around 300k they are failing and need replacing) and that all the resistors are not cracked. Clean the board again after the resolder and checking it.
 

Offline KhronX

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Re: Switch Mode Power Supply
« Reply #5 on: April 14, 2018, 01:25:52 pm »
Might be worth replacing / "refreshing" those two little electrolytics on the primary side (lower-left corner of the top photo).

At least in cheapo ATX power supplies, where the 5V stand-by supply is done with these self-oscillating two-transistor circuits, they relatively often use an electrolytic in a position i've seen called as the "critical cap". When that entirely craps out, the output goes high-voltage.

Not sure that's the case here, but should be easy enough to try out and see if it helps.
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Offline SeanB

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Re: Switch Mode Power Supply
« Reply #6 on: April 14, 2018, 01:55:11 pm »
Lower left is secondary side, on what looks like 15v rails for opamps. They are not regulated or used for feedback at all, just give a voltagewhich will probably be regulated on the main board to give a regulated rail.
 

Offline bob225

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Re: Switch Mode Power Supply
« Reply #7 on: April 14, 2018, 02:24:07 pm »
Pic's where before I reworked and recapped the board (using Panasonic and Nichicon caps). I have retested the transformer (out of circuit) and the inductance and resistance has changed a fair bit on the primary of the 15V side since the first test so I think its not got long to live

Looking at this again and the problems I'm having getting parts and specs, I have ordered a MW RPT-60C what is in UK stock, that makes it more time and cost effective

I will up do a update once I have the parts next week

I have a little Arduino project that I'm playing with in the meantime


Quote
Lower left is secondary side, on what looks like 15v rails for opamps. They are not regulated or used for feedback at all, just give a voltage which will probably be regulated on the main board to give a regulated rail

Correct, There is a 12v reg on the jack board this then feeds the main processor board, the feed back is on the 5v side what feeds the main board

Sorry guys and girls, I'm very rusty with all the theory as its been a good 15+ years since I had to use it in any real situations - and those last 15+ years has been board swapping and minor component replacement
 

Offline Arek_R

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Re: Switch Mode Power Supply
« Reply #8 on: April 14, 2018, 07:14:40 pm »
Whoa, I didn't knew that you can get SMPS with these outputs from MW...
 

Offline bob225

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Re: Switch Mode Power Supply
« Reply #9 on: April 15, 2018, 01:23:51 pm »
I didn't think of actually changing out the psu until it was mentioned above - I have a few MW supplies - the open board type is fine in this application and cheaper than the enclosed version, I will put a mylar type film under it so i don't get any issues
 

Offline bob225

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Re: Switch Mode Power Supply
« Reply #10 on: April 20, 2018, 06:43:39 pm »
Update. All installed and cabled - Just ordered some new tactile switches as I have 2 slightly iffy ones on the control board  :blah:  :blah:  :blah:


 


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