Help me bring back to life an old peavey rage 108 guitar amp! - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 24th August 2012, 07:25 PM   #1
diyAudio Member
 
Join Date: Aug 2012
Location: Caracas
Default Help me bring back to life an old peavey rage 108 guitar amp!

This is going to be a long one

Well my friend was about to throw this amp to the garbage when I said "give it to me, I have a technicall degree on electronics, maybe I can fix it"

So I plugged it and turn it ON without the guitar connected to it. And this high volumen whooom noise started coming out of the speaker. I turned the knobs (volumen, gain for the distorted channel, bass and middle) and made no diference to the noise; only when I turned the knob of the high pass filter the noise seemed to change slightly but rather than that its just noise. Then I plug the guitar and tried to do the same experiments and the noise was the same and it seemed like the guitar signal it is not doing anything, because when I played the guitar the noise did not change and there is no guitar sound coming out of the speaker, just the same noise.

I took out the circuit (unplug the speaker and unscrew the cicuit board) and it looked really disgusting, it was like a roach cementery. So I cleaned it with an electronic cleaning spray and the only thing I could see damaged was a 2200F 35V cap that was swollen. I took it out and did the dgital multimeter test and it seemed to be ok but I replaced it any way. And then put all the things back together and turned it ON and the noise was the same. I took out againg the circuit and started making additional tests, all the resistors are ok and the other caps seems ok.

So the FAQ begins:

1 About the power supply:

It looks ok, It has an AC 120v to 18v and 18v transformer that I could check and is fine. The AC/DC circuit seems ok for what I Could gather it rectifies to 25V DC.

2 About the TDA2040:

This is the main amplifier, so I dont really know if here is where the problem radicates. I mean, if you turn the amp ON and the only thing you can hear is noise regardless of any guitar o knob movement maybe is the amp that is blown. Acording the datashit the maximun voltage (Vs) is 20V but I am meassuring 25V between legs 3 (-VS) and 5 (+Vs). Is this the problem? Is it the power supply? How can I test this amp?

3 About the RC4558p:

This is the pre am. According to the datashit is a dual preamp, does it means that one of the outputs is used for the clean channel and the other output is used for the supersat (disorted) channel? Could it be that is here where the problems is? because if this pre amp is blown it will mess up the input of the main amplifier (TD2040)?

-----

About the images:

- Rage 108 Circuit. Looking around the internet I found this image, it is the circuit for a rage amp but I can really tell if it is the same exact circuit but it looks really similar, my guest is like 85% exactly. Also you can see in the picture that this circuit was dated 10-Aug-92 but the circuit of the amplifier I have is dated 29-Sep-89. In the picture you can see that de voltage for the RC4558p and TD2040 is 27V and 28V and it makes me wonder about the voltage espesification in the datasheet because it spesifies 20V max for both models.

- Actual Amp. This is the picture I took of the amp itself.

-----

I was thinking on replacing the TD2040 but I prefer to wait and see what responses I get about this, and to understand what is happening before making any changes. I would like to know how can I test the amps. I dont know if I will find the replacements in the local electronic parts stores because down here (Venezuela) is not that easy to find some electronic components. Never the less, I will try to find it. Fixing this amp is great oportunity to learn about audio amplifier circuit.


Attached Images
File Type: gif Rage 108 Circuit.gif (89.1 KB, 121 views)
File Type: jpg Actual Amp.jpg (249.4 KB, 116 views)
  Reply With Quote
Old 24th August 2012, 07:42 PM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
You need to determine if your amp runs on a "split" or dual supply. The one in your picture is a single 28 volt rail.

So first step is measure from signal ground to pins 5 pin 3 ? (can't make a pin number out). See if it is like in your circuit or whether instead there is a negative voltage on pin 3 ?.

If single rail then the output pin should be around 14 volts DC and if a dual supply it should be at or near zero volts.

Experience says the TDA will be faulty possily caused by the faulty cap you found.

Usually the
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 24th August 2012, 08:41 PM   #3
diyAudio Member
 
Join Date: Aug 2012
Location: Caracas
Thank you very much Mooly for your fast answer.

I think it is a split supply because it has a transformer with two secundary coils and in each one I meassure 18V AC.

Hear is what I meassure:

Signal Ground (0v) with TDA2040 pin:

pin 3 (-Vs)= 0.7V DC
pin 4 (output) = 12,7V DC
pin 5 (+Vs) = 24,7V DC

Would you think is necesary to replace the TDA2040?
  Reply With Quote
Old 24th August 2012, 09:15 PM   #4
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
I'm not convinced yet

And sorry, I should have asked at the start. If that photo is of your amp then it is single supply.

24 volts on pin 5 and half that on pin 4. That fits with a single rail configuration but doesn't explain why pin 3 is at 0.7volts.

Why do I suspect the TDA ? Because as a service engineer I used to change these type of chips on a daily basis in a lot of audio gear many years ago. There fragile and easily zapped by overloading or shorts etc.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 25th August 2012, 03:13 PM   #5
johnr66 is offline johnr66  United States
diyAudio Member
 
Join Date: Mar 2009
Short the wiper of the "high" pot to signal ground. This will prevent any of the signal from the pre stage getting to the power amp IC. Hum may change a little even if the power IC is damaged, but it should get quiet if it is okay. Also check the supply ripple (check supply caps)
  Reply With Quote
Old 27th August 2012, 09:31 PM   #6
diyAudio Member
 
Join Date: Aug 2012
Location: Caracas
Default Hey thak you!

Quote:
Originally Posted by johnr66 View Post
Short the wiper of the "high" pot to signal ground.
What you are meaning by this is that I could make a bridge between the Pin 1 (in) and the Pin 3 (-VS, Ground) so this way the signal comming from the pre amp will go to ground. Am I right?
Attached Images
File Type: png TDA2040 PinOut.png (19.9 KB, 94 views)

Last edited by delcarmen; 27th August 2012 at 09:41 PM. Reason: I made some mistakes in a sentece
  Reply With Quote
Old 27th August 2012, 09:38 PM   #7
diyAudio Member
 
Join Date: Aug 2012
Location: Caracas
Greetings Mooly

Pin 3 is, for what I could gather, is grounded maybe that is why there is 0,7v (some sligthly potential difference??)

Yes the this is th epicture of my amp!

Thnaks againg
  Reply With Quote
Old 16th January 2013, 12:22 PM   #8
diyAudio Member
 
Join Date: Jan 2013
He you guys is it possible to create from my peavey 108 rage a 110v tranformer unit to a 220 unit. I live in the Netherlands where they have 220v. I bought the Rage 108 in Canada.
Thanks.
  Reply With Quote
Old 16th January 2013, 11:00 PM   #9
JMFahey is offline JMFahey  Argentina
Sin Bin
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Yes.
You need to replace the original 120Vac to 20Vac transformer with a generic one , bought at some Europesn supplier, rated 220 Vac to 20Vac, 1.5Ampere or more.
It may be rated in VA , in which you'll need a 30VA or larger one.
Be careful with 220V mains voltage, work with the amplifier unplugged (turning it off is not enough), doubly so because as seen on that schematic there is no mains power switch, the transformer is always connected to mains and there is no mains fuse.
  Reply With Quote
Old 18th January 2013, 11:28 AM   #10
diyAudio Member
 
Join Date: Jan 2013
Default thanks for replay

Thank god there is a main switch with a fuse (220v 5w) .
My qestion is: how do you measure the transformer wires I tryed to but I do not get eny proper measurements. (By the way it is a working amp) I am curious for I am trying to understand the Transformer.
And thank you for responding.
  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
[Q] traveling to London -- where to go, what to bring back (DIY audio) worker Everything Else 18 20th June 2012 08:59 PM
Bring back the Snark PeteMcK The Lounge 5 28th October 2011 03:37 PM
Is this amp worth bringing back to life? maurycy Tubes / Valves 19 12th March 2011 02:04 AM
Sell back loaded horns for Fe 108 sigma jacques cande Full Range 0 26th September 2005 09:52 PM
Please Help: How to safely bring to life NOS Capacitor? dexter Solid State 8 7th July 2001 12:57 AM


New To Site? Need Help?

All times are GMT. The time now is 02:21 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