Hafler P125 (DH120) One Channel Not Working. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 20th July 2012, 07:31 PM   #1
diyAudio Member
 
Join Date: Jul 2012
Default Hafler P125 (DH120) One Channel Not Working.

Hi,

I've been given a Hafler P125 power amp with on channel not working. The prior ouner opened and checked the fusers and looked around but couldn't find anything. He gave it to me and I want to see if I can fix it.

Where should I start? and what should I be checking? I downloaded the DH-120 manual which looks to be the same as the P125 and it contains schematics and a voltage chart...

Plus any info on this amp would be appreciated.

dinky,
  Reply With Quote
Old 21st July 2012, 12:16 AM   #2
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
bad news... if you don't know what you should be checking it is highly unlikely that you can actually get it working again, unless you get very very lucky. Usually more than one thing fries and lets the magic smoke out...

The voltage chart is not going to help much, because if it is fried, but not totally cooked, running it at full voltage will fry whatever can or will fry...

do some resistance checks if you are sure there is no residual PS voltages around. check the fuses with the ohmeter to start.

if you don't find the problem there, best wait for some other advice, and/or bring it to someone with the gear and experience to do this sort of repair... unless ur guy doesn't mind you having "on the job training" that is.

_-_-bear
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 21st July 2012, 01:17 AM   #3
eyoung is offline eyoung  United States
diyAudio Member
 
eyoung's Avatar
 
Join Date: Aug 2007
Location: Sunny SC,USA 15 min south of Charlotte NC
check out the ginormous DH200 thread , start at the beginning...you will need a basic test bench which starts with a good soldering iron, a variac, and a light bulb test cable(use search function for multiple construction ideas)...study up on safety as there are Lethal voltages inside most power amps....

start reading...

Regards, Elwood
__________________
"Lead me not into temptation...I can find it myself."
  Reply With Quote
Old 21st July 2012, 07:57 AM   #4
fas42 is offline fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 10
In one sense you're in excellent shape, if you're comfortable with using a multimeter, because you have a working channel next to the non working specimen. There is quite a good chance that the DC levels at precisely corresponding points in the 2 copies of the channel circuitry will vary, probably quite dramatically, which should give you excellent clues. If you measure the DC voltage at a circuit point in the good channel, check the same point in the bad, starting with the feed from the voltage rails, then going to the input and working towards the output, you may find something.

I have a Perreaux which died completely in one channel many years ago, nothing obvious whatsoever. No schematic or material to refer to; I used this technique steadily until I got to a simple 1/2 watt resistor: yes, it had gone open circuit. Absolutely nothing to show a problem, no heat stress signs or discolouring at all. Replaced it, we were cooking again! But, there must have been a design weakness, or bad batch of resistors used: the exact same resistor in the other channel went bad a few months later!! The amp went on for years after without missing a beat ....

Warning: unless you're 100% comfortable with trying this technique, do not proceed!!!

Frank

Last edited by fas42; 21st July 2012 at 07:59 AM.
  Reply With Quote
Old 22nd July 2012, 12:19 AM   #5
diyAudio Member
 
Join Date: Jul 2012
Thanks for your suggestions...

Well, I don't think the left channel is blown.

That channel has hiss but at a lower volume. Then there are times where it's working fine...Then it's got crackle and lower volume. So based on this I don't thnk it's blown.

I measured the voltage on those big caps and they are both the same one side is -54.3volts, the other +54.3.

I turned the level knobs, flipped the stereo/mono back and forth, swapped inputs between left and right, but I didn't find anything wrong as far as contacts...

I can tell you that it's a clean amp when it's loud...62 watts stereo.

Is it worth trying to fix?

dinky
  Reply With Quote
Old 22nd July 2012, 03:01 AM   #6
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
I'd try replacing C1 and C4. Electrolytics go bad with age. Those two are signal coupling capacitors.
  Reply With Quote
Old 22nd July 2012, 03:16 AM   #7
fas42 is offline fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 10
Quote:
Originally Posted by dinkyguitar View Post
Thanks for your suggestions...

Well, I don't think the left channel is blown.

That channel has hiss but at a lower volume. Then there are times where it's working fine...Then it's got crackle and lower volume. So based on this I don't thnk it's blown.

...

Is it worth trying to fix?

dinky
Certainly worth trying ... with what you're saying now, sounds like it's a solder joint gone bad, typically on the circuit board. Or a connection within a component, less likely. What I'd suggest doing now, is run it at a low volume with signal coming through, and with a long, slim wooden stick, a stirring spoon from the kitchen drawer held at the wrong end is ideal, gently tap at the leads of the components where they enter the board. Or the components themselves ... gently does it! With a bit of luck you should get a strong reaction at some point, and then all that might be needed is a touch with a hot soldering iron to restore the connection.

Good luck!

Frank
  Reply With Quote
Old 22nd July 2012, 04:45 AM   #8
diyAudio Member
 
Join Date: May 2011
Location: Beverly, Massachusetts, USA
Send a message via AIM to ouimetnick Send a message via Skype™ to ouimetnick
Check connections! These Hafler amps were offered either assembled, OR as a kit. The circuit is fairly simple, so yay for that. Also, replacing the electrolytic capacitors is a good idea. The caps are very old, and could be the issue. But I would first inspect the wiring.
  Reply With Quote
Old 22nd July 2012, 12:04 PM   #9
diyAudio Member
 
Join Date: Jul 2012
Thanks for all the suggestions!

ouimetnick, the caps you mention replacing, your not including those big cap right?

dinky
  Reply With Quote
Old 22nd July 2012, 09:02 PM   #10
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
likely to be a bad transistor, small one. that is a symptom where you get it to work, then a pop then noise... freeze spray, one transistor at a time usually makes it come back on. then you know which one to replace!

It is also possible that you have a broken solder joint on a pad. so you can "touch up" all the solder connections on the bottom of the board if you wish.

_-_-bear
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote

Reply


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
Relays for ESP P125 (4-way LR crossover board) mrwireless Analog Line Level 8 12th June 2011 01:55 PM
hafler dh120 power supply upgrade phillyboy55 Solid State 1 2nd April 2011 01:49 PM
Hafler P500 - One channel quieter than the other Pippi Lindenstroem Solid State 5 14th October 2009 08:44 PM
Hafler P3000: crackling in right channel carpenter Pass Labs 1 7th October 2009 02:37 PM


New To Site? Need Help?

All times are GMT. The time now is 09:47 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2