lm 317t voltage reg - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 8th November 2012, 11:05 AM   #1
diyAudio Member
Join Date: Dec 2011
Default lm 317t voltage reg

Hi , can anyone advise procedure for testing an in-circuit lm317t voltage regulator please? I have an arcam cd73 cd player and am in process of checking the output voltages of all vr's as I have getting no disc error on display, laser is not emitting any light,replaced laser but issue still exists?
The circuit diagram for the laser supply shows this vr to be the regulator,however when testing via a multimeter, I am getting readings of approx 1.2v between pins 1-2 and 2-3, the diagram shows that these should be 3.6v and 5v respectively as this supplys the laser circuit and pll. Am I doing somthing wrong?
any help much appreciated!!!
  Reply With Quote
Old 8th November 2012, 11:21 AM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
Mooly's Avatar
Join Date: Sep 2007
I remember the other thread

I haven't got the circuit on this PC but it sounds like you need to be looking further back (before the regs). Those voltages are to low. If the regs are hot then it could be a short somewhere after these but I suspect not.
Did you do the checks here,
Arcam cd73
  Reply With Quote
Old 8th November 2012, 08:10 PM   #3
diyAudio Member
PlasticIsGood's Avatar
Join Date: Mar 2012
Location: Bradford
1.25V is the over-current shut down voltage of an LM317t.

Considering this regulator is by design operating perilously close to drop-out I assume there is another voltage regulator supplying the 5V, and this may also be a LM317. One scenario to consider is the upstream regulator has shut down due to over-current.

The 317 is pretty bomb-proof. I would check the voltage on the pins of the regulator supplying what should be 5V: if you have plenty volts on its input, and only 1.25 on its output, then there is probably a near short somewhere downstream. If it were a total short there would be no voltage at all.

Check the upstream regulator's regulation pin isn't shorted to ground.

May be something else altogether. Just ideas.

Erratum: the instant I posted this I realised that you were measuring pin to pin rather than to ground. The regulation pin is not grounded, so your voltages may add up nearly right. Since I'm not staring at a LM317t datasheet I don't know which pin is which. So...measure voltage of each pin to ground, to avoid more confusion, please.

Last edited by PlasticIsGood; 8th November 2012 at 08:33 PM.
  Reply With Quote
Old 8th November 2012, 08:29 PM   #4
dacen is offline dacen  Norway
diyAudio Member
Join Date: Jul 2006
Here is the service manual for Arcam CD73. Just download. Whith this one you are in a much better position to do the faultfinding. Good luck.

Categorized Schematics and Service Manuals for free download A-C
  Reply With Quote
Old 9th November 2012, 12:00 PM   #5
diyAudio Member
Join Date: Dec 2011
hi,many thanks for the reply, voltages are from pins 1 to ground and 3 to ground and voltages are around 1.2 - 1.3v, took the ground reading from the body of reg,same as pin2 looking at schematic. Pin volts to ground as per schematic should be 3.6 and 5v?
  Reply With Quote
Old 9th November 2012, 12:06 PM   #6
diyAudio Member
Join Date: Dec 2011
hi,sorry last post was meant to read pins 2 ground and 3 to ground, looking at schematic again pin1 is ground,same as body of regulator,
sorry for confusion,
  Reply With Quote
Old 9th November 2012, 12:34 PM   #7
Xoc1 is offline Xoc1  United Kingdom
diyAudio Member
Xoc1's Avatar
Join Date: Nov 2008
Location: Devon UK
The Lm317 is not grounded as it is an adjustable regulator. The voltage reference is 1.25Volts between pin 1 (adjust) and pin 2 V out, so this is correct.
You are not measuring the voltages with reference to 0V. You will need to look at the schematic and find a 0V Point to measure the regulator input voltage on pin 3 and output on pin 2.
  Reply With Quote
Old 9th November 2012, 12:40 PM   #8
diyAudio Member
sofaspud's Avatar
Join Date: Nov 2005
Location: San Antonio
pin1 is ground,same as body of regulator,
This is incorrect. Pin 1 is Adjust, the tab is pin 2 Output.
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 9th November 2012, 01:00 PM   #9
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
Mooly's Avatar
Join Date: Sep 2007
Tom... did you check the fuses first.

Look at the PSU on page 8 of the manual.
Connect the negative lead of your meter to any ground point such as the audio output ground on theaudio output phono socket. Yes

Now measure the plus 11 volt supply which you can find on one end of D521. The other end of the diode should have 8 volts.

Thats your first step. Are those two voltages correct.

If they are, then you need to see if the 11 volts is reaching U502. Again we can easily measure on the diode D516. There should be 11 volts on one end and 5 volts on the other.

Again if that is OK then we now move to U507 and again by measuring on diode D525 we should see 5 volts on one end and 3.6 on the other.

Report back with your readings (and don't forget the fuses)
Attached Images
File Type: jpg Capture.JPG (57.3 KB, 316 views)
File Type: jpg Capture2.JPG (36.3 KB, 306 views)
File Type: jpg Capture3.JPG (40.3 KB, 307 views)
  Reply With Quote
Old 9th November 2012, 01:57 PM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
Clip your black probe to audio ground, either inside the player or at an RCA.
Leave that there.

Using one hand with the red probe, go around carefully taking voltages with reference to that ground.
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Hi voltage Jung super reg grataku Solid State 33 13th July 2011 05:33 AM
FBT-00-031 voltage reg jan.didden Parts 5 22nd December 2007 09:46 AM
Discrete voltage reg for SLA Capt Zach Power Supplies 3 23rd July 2007 11:12 AM
Russ Andrews voltage reg stoolpigeon Solid State 10 8th July 2007 11:04 AM
Voltage reg for front end. CBS240 Solid State 7 31st December 2005 08:04 AM

New To Site? Need Help?

All times are GMT. The time now is 01:54 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2