Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Problems recapping phase linear 400
Problems recapping phase linear 400
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
Reply
 
Thread Tools Search this Thread
Old 3rd February 2011, 03:40 AM   #1
BigE is offline BigE  Canada
diyAudio Member
 
BigE's Avatar
 
Join Date: Aug 2008
Location: Toronto
Default Problems recapping phase linear 400

I swapped out the caps on the PC board again. This is PC14B.

The Service Manual can be found at www.hifiengine.com


All the caps were inserted with the correct polarity. The amp was working just before the swap.

I carefully swapped them ALL out with Elna Silmic II, in the correct orientation. I had some trouble with the larger caps, and could not insert them all the way in. These were C3.

After doing the work, I plugged it in and checked the DC offset.

Sadly, it was 75 volts on both channels.

No pop, click, nothing, no blown fuse! Meters do NOT deflect.

Just 75 volts DC at the outputs of both channels.

Got +/- 80 at the filter caps -- they are jensen 4-pole I put in months ago.

Some traces were lifting, as this operation had been done before at least twice, once by me.... the pcb is in bad shape. in several locations, the traces have been replaced with wire.

I'm totally lost at this point.

The output drivers appear to be ok from the service manual, the resistors R37 and R36 measure ok -- both are 146 ohms.

That leaves the output transistors. But, they too seem fine. I may be measuring wrong. Some help here would be awesome.

But what the heck? I was just changing the caps, nothing else. I did not touch the harness, all seems well.

Any clues as to the next step?

Thanks!

Last edited by BigE; 3rd February 2011 at 03:46 AM.
  Reply With Quote
Old 3rd February 2011, 04:36 AM   #2
Conrad Hoffman is offline Conrad Hoffman  United States
diyAudio Member
 
Join Date: Mar 2007
Location: Canandaigua, NY USA
It's been so long since I've seen a PL400 board that I don't remember what they look like. If they are double sided boards, could you have lost connection at a pad where the top connects to the bottom?

CH
__________________
I may be barking up the wrong tree, but at least I'm barking!
  Reply With Quote
Old 3rd February 2011, 06:35 AM   #3
stratus46 is offline stratus46  United States
diyAudio Member
 
Join Date: Nov 2009
Location: Los Angeles
The output devices are not blown. They 'being 'told' to go to +75. If any had failed you'd see fuses blowing. What is the Voltage on the collector of Q5? If it's +75 then check collector of Q4. It should be -79 - as stated on the schematic. What's the base of Q2?

You've broken the negative feedback loop and the bootstrap resistors (R17 and R18) have nothing to pull them down. Nothing really catastrophic has happened yet but you've likely left a broken trace or two. OR you may be missing the -80 supply to the board. Start measuring. In this particular case it might be safer to run on reduced Voltage with a Variac. More info will get better answers.

G
  Reply With Quote
Old 3rd February 2011, 06:46 AM   #4
MOER is offline MOER  United States
diyAudio Member
 
Join Date: Aug 2003
Location: NEWBURY PARK CA
Default Phase Linear 400

We have spare PCBs from 400s which we rebuilt using our own PCB design.

All the PLs we refurbish but keep the original PCB we do the following:

Convert to full complementary output stage
Degenerate the differential amplifier's emitters
Install a constant current source for the differential amplifier
Install base stoppers on the 40327 and 2N5415/MM4003 predrivers.
We use MJ15003/MJ15004 for PL400s and MJ1500 series for 700s
Remove the stupid input series resistor on the diff amp as it causes so much phase shift.
Change the value of the down feedback resistor to 620 ohm.

Steve Mantz
Zed Audio
  Reply With Quote
Old 3rd February 2011, 03:20 PM   #5
BigE is offline BigE  Canada
diyAudio Member
 
BigE's Avatar
 
Join Date: Aug 2008
Location: Toronto
Quote:
Originally Posted by stratus46 View Post
The output devices are not blown. They 'being 'told' to go to +75. If any had failed you'd see fuses blowing. What is the Voltage on the collector of Q5? If it's +75 then check collector of Q4. It should be -79 - as stated on the schematic. What's the base of Q2?

You've broken the negative feedback loop and the bootstrap resistors (R17 and R18) have nothing to pull them down. Nothing really catastrophic has happened yet but you've likely left a broken trace or two. OR you may be missing the -80 supply to the board. Start measuring. In this particular case it might be safer to run on reduced Voltage with a Variac. More info will get better answers.

G
I'll make those tests this evening -- thanks! I feel better about it.

The PC board is getting power.

I think caps C3 may be the issue, as they have thicker leads than the others. It was a real chore to get them through the PC board, then the traces did lift.

The rest of the caps went in uneventfully, so maybe the traces broke when taking the others out?

Of course, this board has been worked on by so many other hacks, not just me, that there are lifted traces and patches all over it.

Thanks, I'll post the voltages later.

Maybe this is a good time to replace the ancient overly stiff harness?
  Reply With Quote
Old 3rd February 2011, 03:26 PM   #6
BigE is offline BigE  Canada
diyAudio Member
 
BigE's Avatar
 
Join Date: Aug 2008
Location: Toronto
Quote:
Originally Posted by MOER View Post
We have spare PCBs from 400s which we rebuilt using our own PCB design.

All the PLs we refurbish but keep the original PCB we do the following:

Convert to full complementary output stage
Degenerate the differential amplifier's emitters
Install a constant current source for the differential amplifier
Install base stoppers on the 40327 and 2N5415/MM4003 predrivers.
We use MJ15003/MJ15004 for PL400s and MJ1500 series for 700s
Remove the stupid input series resistor on the diff amp as it causes so much phase shift.
Change the value of the down feedback resistor to 620 ohm.

Steve Mantz
Zed Audio
That's a lot of work! My PC board is so beat up, it would be great to have it replaced. Any chance I can get a PL14 from you?

My amp was the latest version, with the 10K and 39K voltage divider in front of the first differential pair.

I've changed that to 15K and 59K, to be more tube friendly. When running, the DC offsets were 66 and 75 mV, the bias was .43 volts, the lowest it would go is .4 Not bad for an old amp I thought....

I don't understand your phase shift comment.... How can an input resistor cause phase shift? I and V remain in phase across a resistor.... could you please shed some light on this? thanks.
  Reply With Quote
Old 3rd February 2011, 03:52 PM   #7
llwhtt is offline llwhtt  United States
diyAudio Member
 
Join Date: Jun 2008
Location: SoCal
Check all of the wires to and from the PCB, since you've been moving it around a wire may have broken either at the board or at the output section. Next check the wires to the bias transistors, red, brown and black. The last 400 I rebuilt was working fine until I screwed all back together and it didn't work. Disassembled one more time and found the leads to the bias transistors had broken.

Craig
  Reply With Quote
Old 3rd February 2011, 04:22 PM   #8
BigE is offline BigE  Canada
diyAudio Member
 
BigE's Avatar
 
Join Date: Aug 2008
Location: Toronto
Thanks, I will check each one, especially the bias. Could I measure the bias voltage to make sure? If the bias checks out, then the feedback loops on the PC board are broken.

I think I should replace all of the wires while I am at this... I'll dip the ends
into flux, tin them, dip into flux again and use the existing solder on the pads to connect. Those pads are really close together.
  Reply With Quote
Old 3rd February 2011, 07:19 PM   #9
llwhtt is offline llwhtt  United States
diyAudio Member
 
Join Date: Jun 2008
Location: SoCal
I used my little Dremel drill press and drilled holes thru the pads and stuck the wires thru the board like normal. Replaced all of the wiring with something more flexible, the old wire is very stiff by now.

Craig
  Reply With Quote
Old 3rd February 2011, 07:20 PM   #10
BigE is offline BigE  Canada
diyAudio Member
 
BigE's Avatar
 
Join Date: Aug 2008
Location: Toronto
That is a fantastic idea! Very cool, thanks!
  Reply With Quote

Reply


Problems recapping phase linear 400Hide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Phase Linear 400 BigE Solid State 20 7th January 2011 03:44 PM
Phase Linear 700 Series Two recapping releone71 Solid State 4 12th March 2010 08:32 PM
Need help fixing an odd Phase Linear 400 blue lander Solid State 91 20th August 2009 03:46 PM
Phase Linear 400 Question mrfeedback Solid State 49 9th May 2009 04:59 PM
Phase Linear 400, SERIOUS AC! Planerguy Solid State 41 29th March 2009 03:41 AM


New To Site? Need Help?

All times are GMT. The time now is 03:27 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki