Fender FM212R Problems - Page 9 - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 10th January 2013, 06:37 PM   #81
diyAudio Member
 
chris661's Avatar
 
Join Date: Feb 2008
Location: Sheffield
Blog Entries: 8
Turn all the dials down again.

Use a normal guitar lead, connect preamp out to power amp in.

I suspect dirty switch contacts.
  Reply With Quote
Old 10th January 2013, 10:02 PM   #82
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Quote:
I installed the insulators as instructed and hooked the power and the current limiter lit but just barely.
Quote:
So I hooked directly to power and flipped the switch
Between Quote 1 and Quote 2 I don't see: "I measured all voltages and found them normal".
Sorry, I understand your anxiety, but please let's slow down a bit, we are real close anyway.
I've just arrived to my shop after travelling all over the city buying parts (such as nails/glue/speaker cloth/tapestry staples/paint) so *now* I won't be suggesting an answer, but stay tuned that late at night or tomorrow morning I'll suggest some tests.
But rest assured that we are close.
Good luck.
  Reply With Quote
Old 11th January 2013, 12:36 AM   #83
diyAudio Member
 
badraven's Avatar
 
Join Date: Dec 2012
Location: The heart of the South, in other words -Redneck Territory lol
Sorry, I wasn't trying to jump the gun. I thought I was following the proper procedure. I will await your instructions. Thank you.

BR
__________________
If at first you dont succeed, perhaps it isn't your bag. Lol...
  Reply With Quote
Old 11th January 2013, 04:03 AM   #84
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Fine.
I understand you pulled the TIP screws, added the nipples and re mounted them.
The big question is: measure again from collectors (center legs ) to ground, do you still have those shorts you measured before?
I guess not, but measuring beats guessing big time.
If not, turn amp on, please measure +/-V rails and DC voltage at the speaker output.
I expect normal (say +/- 30 to 40V rails, less than 100mV DC at speaker out) .
If so, measure bias voltage , from Q18 to Q19 base (left pin of TIP31/32) I expect around 2.5V DC or current, measure voltage from Q20 to Q21 emitters (right pin), I expect around 10mV DC.
Thanks.

PS: still always with the bulb limiter.
  Reply With Quote
Old 11th January 2013, 04:23 AM   #85
diyAudio Member
 
badraven's Avatar
 
Join Date: Dec 2012
Location: The heart of the South, in other words -Redneck Territory lol
I did check the collectors. None of them are shorted now. I did that as soon as I added the insulators. THEN I used the current limiter. THEN I tried it without the current limiter. I didn't get the speaker measurement, sorry about that. I will get that for you.

"measure bias voltage , from Q18 to Q19 base (left pin of TIP31/32) I expect around 2.5V DC or current, measure voltage from Q20 to Q21 emitters (right pin), I expect around 10mV DC.
Thanks"


I know where you are telling me to place the red lead but where am I hooking the black lead for these tests?

Thanks!
BR
__________________
If at first you dont succeed, perhaps it isn't your bag. Lol...
  Reply With Quote
Old 11th January 2013, 07:39 AM   #86
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
"I know where you are telling me to place the red lead but where am I hooking the black lead for these tests?"

He asked for the voltage between the bases of Q18 and Q19. (the left leg of each) SO you put your red lead on one,and the black lead on the other.

We are measuring the voltage from one to the other.


Think of a shelf on your wall. We could ask how high it is above the floor. That would be like the voltage to ground. Or we could ask how long the shelf is - the distance end to end. The distance from one end to the other. It wouldn;t matter how high off the floor it was, we wanted the length. I hope that analogy is not confusing.
  Reply With Quote
Old 11th January 2013, 08:56 AM   #87
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
If u can buy a crystal phone(the high impedance earphone), u can find the faulty stage and don't have to look around the total amp, for the fault.

Gajanan Phadte
  Reply With Quote
Old 11th January 2013, 11:48 PM   #88
diyAudio Member
 
badraven's Avatar
 
Join Date: Dec 2012
Location: The heart of the South, in other words -Redneck Territory lol
Default Enzo

Enzo

Thanks for clarifying things for me.
I wasn't having a problem differentiating between the two different tasks he presented me with. I was having a problem with the procedures of accomplishing them. I am learning the lingo and the associated procedures but I still have a ways to go, but I will get there with help from folks like yourself. Thanks!

BR



He asked for the voltage between the bases of Q18 and Q19. (the left leg of each) SO you put your red lead on one,and the black lead on the other.

We are measuring the voltage from one to the other.


Think of a shelf on your wall. We could ask how high it is above the floor. That would be like the voltage to ground. Or we could ask how long the shelf is - the distance end to end. The distance from one end to the other. It wouldn;t matter how high off the floor it was, we wanted the length. I hope that analogy is not confusing.[/QUOTE]
__________________
If at first you dont succeed, perhaps it isn't your bag. Lol...
  Reply With Quote
Old 11th January 2013, 11:49 PM   #89
diyAudio Member
 
badraven's Avatar
 
Join Date: Dec 2012
Location: The heart of the South, in other words -Redneck Territory lol
Quote:
Originally Posted by gmphadte View Post
If u can buy a crystal phone(the high impedance earphone), u can find the faulty stage and don't have to look around the total amp, for the fault.

Gajanan Phadte
If you are going to offer a suggestion like this it would help if you explained how to make use of the info. Thanks!

BR
__________________
If at first you dont succeed, perhaps it isn't your bag. Lol...
  Reply With Quote
Old 12th January 2013, 02:21 AM   #90
diyAudio Member
 
badraven's Avatar
 
Join Date: Dec 2012
Location: The heart of the South, in other words -Redneck Territory lol
Amp unplugged, Collector to ground:
Meter Setting Diode Q20 = 1.516 / Q18 = 1.503 / Q19 = .489 / Q21 = .488
Meter set to ohms: Q20 = 4.01 / Q18 = 4.6 / Q19 = 2.02 / Q21 = 1.83

Amp plugged in through current limiter:
Q18 to Q19 base pin bias (left pin to left pin) = 1.65V DC
Q20 to Q21 Emitters (right pin to right pin) = 110.5mV DC
No Speaker connected: P1 to P2 = 9.2 mV DC

P3 to P4 = 023 VDC
P3 to P5 = 1.45
P4 to P5 = .45

On the schematic TP3 is (+42 rail) TP4 is (-42 rail) I cannot locate either terminal on the PCB. However the schematic shows R144 and R145 to be connected to both rails. I am not sure which side of each resistor is + or - See pic - Touching the end of each resistor on the side towards the strippers shows 63VDC The side closest shows 31.45VDC

Just figured this out.
The collector legs of Q21 and Q19 are on the -42 rail = 32.84VDC
The collector legs of Q18 and Q20 are on the +42 rail. = 32.64VDC


As a side note, when I touched the test lead to to R144 (left) its loose. The metal leads seem to be ok but the body moves easily. I checked the ohm (amp unplugged) of R144 (top side) and get 340 ohms. When I flip the PCB over and test the terminals at the solder joints, I get an open. R145 show 340 on top and bottom.

I haven't done anything yet and won't until I get instructions from you. I think the joints need to be desoldered and resoldered.

I await your instructions.

BR



Quote:
Originally Posted by JMFahey View Post
Fine.
I understand you pulled the TIP screws, added the nipples and re mounted them.
The big question is: measure again from collectors (center legs ) to ground, do you still have those shorts you measured before?
I guess not, but measuring beats guessing big time.
If not, turn amp on, please measure +/-V rails and DC voltage at the speaker output.
I expect normal (say +/- 30 to 40V rails, less than 100mV DC at speaker out) .
If so, measure bias voltage , from Q18 to Q19 base (left pin of TIP31/32) I expect around 2.5V DC or current, measure voltage from Q20 to Q21 emitters (right pin), I expect around 10mV DC.
Thanks.

PS: still always with the bulb limiter.
Attached Images
File Type: jpg R144 R145.jpg (937.0 KB, 28 views)
__________________
If at first you dont succeed, perhaps it isn't your bag. Lol...
  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
Fender help Docc25 Instruments and Amps 3 2nd January 2013 10:18 PM
1970s fender champ givin me problems beauxweiss Instruments and Amps 4 21st February 2012 04:53 PM
MiniWatt N3 problems, oscillation thumping and RF/motor problems. Destroyer OS. Tubes / Valves 18 6th July 2010 12:14 AM
Fender Adjustments JDeV Tubes / Valves 6 7th April 2006 08:17 PM
Another Fender on the bench. Netlist Tubes / Valves 3 6th March 2004 08:03 AM


New To Site? Need Help?

All times are GMT. The time now is 12:52 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