Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Power Supplies and Power Supply Design
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools
Old 02-09-2019, 03:55 AM   #1
madan1
Badcaps Veteran
 
Join Date: Nov 2016
City & State: Sofia
My Country: Bulgaria
I'm a: Knowledge Seeker
Posts: 284
Default SMPS low Vout

Hi there.

A quick one - BENQ projector SMPS, according to the SM there should be 2.5V, 5V and 12V at any time ( good ol' times, when there were no eco regulations ).
What I see though, is - +2.7V, +4.8V and -9.9V (I guess the polarity is irrelevant ).
So, the projector starts, and shows some functionality, but is not powering up the ballast ( there is power supply, but no command I guess ). Before troubleshooting more the MB ( there was a puffing smd capacitor for which I'll upload some media in the main cap thread ) and the ballast, I'd like to get the Vs within the specs. The 2.5 and 5V seem to be within the limits, but the 12V is low.
What I've done so far is to desolder the c707 and measure it... and it its fine - 707uF ESR 0.01.
What's next?
Attached Files
File Type: pdf MP720_C304_Schematics Drawing.pdf (113.5 KB, 4 views)

Last edited by madan1; 02-09-2019 at 05:00 AM..
madan1 is offline   Reply With Quote
Old 02-09-2019, 07:53 AM   #2
stj
Great Sage 齊天大聖
 
stj's Avatar
 
Join Date: Dec 2009
City & State: Europe
My Country: some shithole run by Israeli agents
I'm a: Professional Tech
Posts: 20,079
Default Re: SMPS low Vout

could be the diode, BUT - is it running hot?
i'm thinking something may be overloading it.
stj is offline   Reply With Quote
Old 02-09-2019, 08:12 AM   #3
madan1
Badcaps Veteran
 
Join Date: Nov 2016
City & State: Sofia
My Country: Bulgaria
I'm a: Knowledge Seeker
Posts: 284
Default Re: SMPS low Vout

Thanks for the reply... but it's my bad. I was measuring it wrong. In the SM there is no connector pinout and I assumed that it was rail-gnd rail-gnd... aligned, but it turned out that the ground are only 4 pins on one of the rows. Probably if I had paid more attention to the traces on the PSU board instead of focusing on the "usual suspects" would have saved me lot's of time .
Now, with the correct pinout, I'm able to read 2.63, 5.07 and 11.9V when the unit is "on". By the way, all caps are nichicon and all which I have measured are at least the uF shown on their labels... and that thing is 10+ years old. Well done nichicon
madan1 is offline   Reply With Quote
Old 02-09-2019, 08:20 AM   #4
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 1,209
Default Re: SMPS low Vout

Quote:
Originally Posted by madan1 View Post
By the way, all caps are nichicon and all which I have measured are at least the uF shown on their labels... and that thing is 10+ years old. Well done nichicon
Just for good measure I would recommend recapping this unit specifically the capacitor that are less than 100uf
__________________
9 PC LCD Monitor
6 LCD Flat Screen TV
30 Desk Top Switching Power Supply
10 Desk Top Power Supply
10 Battery Charger Switching Power Supply for Power Tool
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
25 Servo Drives 220/460 3 Phase
6 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps
sam_sam_sam is offline   Reply With Quote
Old 02-09-2019, 08:33 AM   #5
madan1
Badcaps Veteran
 
Join Date: Nov 2016
City & State: Sofia
My Country: Bulgaria
I'm a: Knowledge Seeker
Posts: 284
Default Re: SMPS low Vout

Once I get the projector going I might recap it... for troubleshooting purposes I guess it's fine at the moment.

By the way, here is Smokey the capacitor - https://www.badcaps.net/forum/showth...404#post880404
madan1 is offline   Reply With Quote
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2019
Powered by vBulletin ®
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 09:01 PM.
Did you find this forum helpful?