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

Pass Labs This forum is dedicated to Pass Labs discussion.

Forte Model 3 - One channel running hot
Forte Model 3 - One channel running hot
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 4th September 2018, 05:01 PM   #1
Vikinglander is offline Vikinglander  United States
diyAudio Member
 
Join Date: Aug 2018
Location: Wisconsin
Default Forte Model 3 - One channel running hot

Hello Forum -

I have enjoyed my Forte Model 3 running it into a pair of Magnepan 1.6 with great results. The amp was left one night and since then I noticed the left channel running quite hot (hot to the touch) compared to the right. I have not used it since with the exception to get you theses images. I have not messed with the bias but it looks like that adjustment has slipped (? as visually inspected by the amateur). I have not been able to find what test point I should use to compare the two sides to decide if a bias adjustment is the next step. Note, the IR images is after 5 seconds on time. Any help would be greatly appreciated.
Attached Images
File Type: jpg Forte Model 3 Amp Back Panel.JPG (398.2 KB, 222 views)
File Type: jpg Forte Model 3 Amp Left Channel 1.JPG (344.6 KB, 223 views)
File Type: jpg Forte Model 3 Amp IR 1.jpg (87.1 KB, 228 views)
File Type: jpg Forte Model 3 Amp IR 2.jpg (84.3 KB, 222 views)
  Reply With Quote
Old 4th September 2018, 06:03 PM   #2
Zen Mod is online now Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Forte Model 3 - One channel running hot
compare DC voltages across these gray biggie resistors - hot vs. colder channel

(so no signal needed)

then write here

DVM on , say , 200mV range or next one , if needed
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote
Old 4th September 2018, 07:43 PM   #3
ColinA123 is offline ColinA123  United Kingdom
diyAudio Member
 
Join Date: Jun 2017
Location: Shropshire
Also note, you seem to have a hotter tag on the R/H rectifier.

May be nothing but worth cleaning / reseating.
  Reply With Quote
Old 6th September 2018, 04:34 PM   #4
Vikinglander is offline Vikinglander  United States
diyAudio Member
 
Join Date: Aug 2018
Location: Wisconsin
Default Forte Model 3 left heat sink running hot.

OK, finally got around to getting some voltage drops over the large, high wattage resistors (grey) and comparing hot side to cool side. Please note that I aggressively cooled with heavy duty force air the hot channel (left) and was not able to confirm left side still gets hot-to-the-touch for that reason. I didn’t want to stress a weak component further if is on its way out, I guess.

The voltage drops didn’t seem off to me and the differences were relatively minor between right and left channel. See what you think.

I numerated the resistors 1 -2 - . . . top row, front to back of the amp the starting at 6 -10 bottom row, front to back if that has any bearing in the analysis.

Hope this makes sense and thank you very much for the responses. Looking forward to learning more!!
Attached Images
File Type: jpg Voltage Drop Data.JPG (30.5 KB, 191 views)
File Type: jpg Voltage Drop Analysis.JPG (30.7 KB, 52 views)
File Type: jpg Circuit Board View.JPG (30.8 KB, 52 views)

Last edited by Vikinglander; 6th September 2018 at 04:42 PM.
  Reply With Quote
Old 6th September 2018, 06:30 PM   #5
Zen Mod is online now Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Forte Model 3 - One channel running hot
now I'm realllllly puzzled , too ?!?!?

it's against any logic

can you measure that "hot to touch" with modern thingie - "laser" thermometer?

maybe difference is factually small , but our palms being hysteric .....

as guide , Papa's table attached
Attached Images
File Type: jpg TEMP.jpg (39.5 KB, 55 views)
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote
Old 6th September 2018, 06:43 PM   #6
Vikinglander is offline Vikinglander  United States
diyAudio Member
 
Join Date: Aug 2018
Location: Wisconsin
Thank you, Zen Mod. Stay tuned!
  Reply With Quote
Old 7th September 2018, 02:16 AM   #7
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
Quote:
Originally Posted by Zen Mod View Post
...can you measure that "hot to touch" with modern thingie - "laser" thermometer?...
His 4th image IS a "laser thermometer". Actually an IR camera. The usual laser-tool measures one spot, the FLIR measures the whole scene at once. It may have a way to put numbers on a specific spot, which may be of interest. However the mellow blue on one side, mild pink on the transformer, and bright red-yellow on the other side, sure shows there is a BIG difference.

Yet not reflected in the emitter(?) resistor voltage drops.

I'd want supply rail voltages. Maybe the hot side is correct and the cool side is not getting full supply voltage.
  Reply With Quote
Old 7th September 2018, 06:50 PM   #8
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Forte Model 3 - One channel running hot
The next thing is to evaluate the actual resistances or channel current.
  Reply With Quote
Old 10th September 2018, 05:01 PM   #9
Vikinglander is offline Vikinglander  United States
diyAudio Member
 
Join Date: Aug 2018
Location: Wisconsin
Smile Left channel WAS hot

Thank you very much for all the responses!

I finally have some actual temperature from the heat sinks. In addition, I have resistance and subsequent current values for all the high wattage resistors assuming a measurement is not affected by neighboring components in the circuit. The resistances were measure cold and power off!

Sure looks good to me and indicates there’s nothing wrong with this amplifier. In addition, all this attention has managed to make the problem go away. This would have been quite frustrating if it was not for a lose screw I discovered during a check-all-connection exercise as suggested by Colin123 earlier.
Yes, the amp was re-capped prior to me getting it and the shop must have missed it during re-assembly.

I will hang my hat on that being a fix for now. Both sides run just warm at 42 and 43 C after 5-minute run time. Hand warmers versus bleeding hot!

Please note, the IR images are self-ranging to show that widest spread in color. Earlier images were taken when significantly hotter, but I failed to turn on the actual temp readout function.

I was also speculating that it might be oscillation set this off and that I could test this by shorting the input (?) but I will forgo this for now.

Finally, I noticed that both my thermistors (I think they are) are floating off the heat sink. The paste gave away over time. Any suggestions for best practice to re-attaching them?

Again, thank you for your help!
Attached Images
File Type: jpg IR Image of Ballanced Forte 3 1.jpg (92.5 KB, 39 views)
File Type: jpg IR Image of Ballanced Forte 3 2.jpg (106.7 KB, 25 views)
File Type: jpg IR Image of Ballanced Forte 3 3.jpg (110.2 KB, 19 views)
File Type: jpg Forte 3 Resistor Data.JPG (75.2 KB, 28 views)
File Type: jpg Forte 3 Channel Current Analysis.JPG (30.4 KB, 29 views)
File Type: jpg Forte 3 Heat Sink Thermister.jpg (82.2 KB, 56 views)
  Reply With Quote
Old 10th September 2018, 05:51 PM   #10
Zen Mod is online now Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Forte Model 3 - One channel running hot
just put blob of thermal go in between NTCs and heatsink and try leaning them slightly closer

don't fret , they're close enough
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote

Reply


Forte Model 3 - One channel running hotHide 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
Converting Forte Model 3 to Model 1a LouieTheG Pass Labs 2 7th May 2015 05:42 PM
Forte Model Six help dim1 Solid State 0 29th November 2014 07:55 PM
Forte Model 1 hum tonywood Solid State 2 20th May 2014 09:10 PM
Forte, Model 6 with smoked left Channel Drewgy Solid State 0 8th July 2013 02:37 PM
Forte Model 44 neekos Solid State 0 13th November 2010 10:55 PM


New To Site? Need Help?

All times are GMT. The time now is 09:41 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki