Clean the headphone jack to make sure dirty contacts are not shunting the speaker signal. So it works with headphones but the pots are dirty. Get some Deoxit or other type of cleaner and spray out the dirt build up in the pots. Also, would be a good idea to make sure the speaker output wires are really connected.   

If you are at all unsure or worried about taking live voltage readings then keep researching all you can about safety precautions. Like the one's that say take off all your rings on your fingers before testing voltages.  :tu:

How you described the testing is correct: Ground is typically your chassis and it is a good idea to just clip it in place. At that point, powered off, I like to set DMM for a continuity test to make sure I have grounded through to the circuit board. Clip black probe to chassis and test for continuity. For example, test continuity from chassis to something you know is ground on the board. Then yes start to record voltage readings in each different place on the board. If you are unsure about something ask before testing but it is really straightforward for the most part. As you do it more you get more comfortable but just never get too comfortable and always be on your guard.

<Mensur...> I think he meant to solder or clip a wire to the master (red channel) middle leg that then led straight to the hot (tip) part of the input jack as to force the full signal into input on that channel. Well that would be interesting to know if that works.

<J M Fahey> As Juan is saying to look at the Green channel and the voltages that are sought out on that channel and then compare and contrast any discrepancies since they are almost identical. If you look at the Green channel there are voltages posted in the schematic. However, on the Red channel of the schematic there is not much to show for voltage so you have to cross reference the circuit. These circuits are almost the same or are identical as Juan said... So, look closely and cross reference any voltages in a way to find a bad component or loss of voltage.

What I meant about about a break in a leg on the Green cap is in reference to the green part on the leg being cracked off. I am not saying the whole leg is cracked off the circuit... just to note. I have seen these types of tone caps w/ cracked insulation that lead to total loss of effect signal in (for example) a Boss DD-3. That one ceramic cap killed the entire delay effect from working.

I think Juan made a great point that looking at the components of the amp is not gonna fix it in most cases.

If I was to question one two things by your pictures alone it would be by the double potted tone potentiometer and those two IC chips(not sure what those are right of the Tone Clipping pot...) I think they are IC's I have an RG80 combo but it does not have that component there so I have no idea what it is used for... Anyway that thing looks cracked or something...

Another thing thing is the green 1KV 202M signal cap looks like the leg has torn and might be leaking... But that is probably not the problem but still can be replaced later on. However, I know that those ceramic caps when the legs are torn can cause a huge loss to signal overall. Not always the case but something to chew on just by looking at pics.

My advice is download the schematic from this link below... Look for post from Stratorius for the Schematic info then go right below his post and READ ENZO's post. Now we can assume you completely removed all the solder from the joints of the main Filter caps... I hope. Just reflowing the solder may not be enough... If not do this now as it points to loose solder joints on the caps. Change the caps too as they are nearly 25 years old.>>> But this might be the link you were looking for too.??>>>

http://www.ssguitar.com/index.php?topic=1673.0

Also, in addition to asking for the schematic which I think I will try to ask them myself too. Where did you purchase this replacement kit? I mean I saw on that first site that there were no more kits available... That would be nice for others to know where you bought this... a link...

I definitely interested in the schematic to this board and anyone here too. You did Great work on this amp Captain. Could not do it without the great techs here (they know who they are) but you also played into the factor of the amp repair being successful too! Yup standing on the shoulder of others should feel great no matter how high you rise.

If I was buying the guitar amp as I do wanting to resell the amp I would give you $20USD. If I then sold it to someone who was actually going to use the amp I would ask $40-50USD.

P.S. I pay about $5-10 for broken amps too! Not much but if it is broken and you don't want to or know how to fix it, then it is worth something to both parties. I compare these amps to the Epiphone ep1000 which is usually a tweed Korean amp that sounds actually rather nice.

http://www.amparchives.com/album/Fender/Schematics/slides/Fender%20Squire%2015%20Schematic.html

What sort of skills do you possess? Do you have DMM? Do you have skills soldering? Etc.... Etc... Etc...

This is a very simple amp to learn on and can be fixed without much money invested in parts. Look at the PCB board for bad solder joints on the filter caps or anything else that might look suspect. If you have a DMM (or any multimeter) test for DC Voltage at the speaker output leads. Test voltage on the BR or rectifier diodes/filter caps. Also, test voltage on the opamp chips. Basically, we need you to be able to take apart the amp and understand how to do these tests to help fix the problem. As Loudthud has stated it is probably the output transistor that is fried. So, test to see if you are getting voltage on the speaker output leads first to make sure.

My final thought is that 3 FETS will not get the job done here on this replacement circuit. However, I have a question as to whether J175 Q1 plays into the that role of making the logic of the switch come to life?

Looking at the datasheet pin 1 is ground...

Pin2 is marked as "A" on the data sheet, it ties over to the base of Q1 J175 and I think you should look at the transistor there to makes sure it is sound. Perhaps is was Zapped out of the circuit too!

Pin3 and Pin4 are tied together which is S1 and S2 tied to Pin 6 and Pin7 S1/S2. This is the switch.

So that leaves out pin5 and 8 as voltage carriers.

Looking at the picture pin1 and pin2 on the chip PV replacement (refer to picture) look like these ones to me, but not quite sure of this as a fact. Just a hunch after looking at it and studying it's layout. So, one channel is shorting to ground maybe due to the Q1 malfunction. To me it would seem that sure the pin out could be different on the replacement it is for a 604 chip but not DPST. Maybe this is only for SPST type switch and needs some modifications? Not sure I know exactly what I am saying here... Maybe even typing something silly will cause someone more knowledgeable to explain what could be going wrong here...?

Also, the more expensive other module you saw on that site is discontinued and really was the kit version to build what you have now. So, that is not reason why this won't work.



http://www.ti.com/lit/ds/slas042/slas042.pdf

Edit: Too funny a double posting... Also, you said on the main board there was nothing tracing anything to pin6? Explain which pins are what according to the picture... Also, show a link to the other module you thought it could have been. I might even have DPST thing wrong and it is as Juan said a "SPDT" type circuit needed. These things always confuse me at first... Or rather as Juan really put it... "Two independently driven SPST switches" Now that the solution here...

Makes you wonder what happened to that amp!! LOL    :trouble

Good job troubleshooting ya guys!! I look forward to the end result of a guitar passing signal through the amp soon.

Sorry to interrupt into this great thread... I am really enjoying reading along following all of what is being looked at on the schematic.

I have a question that even the OP might have wondered as well... Can we take voltage tests off of pins 4 and 8 on all the op amp chips? I mean sure we can test voltage there to check but why would that not prove to be useful numbers?

I am following the idea of IC2 being lifted first and then checking IC7. I think something is telling us that +/-24V rails could have something tied into the problem too. Maybe looking at Q2 and Q3 closer(later on down the line of course) and D8 is in there too. IC7 is giving me that gut feeling even more now. Also, have we confirmed what is measured on the 24v rails? Excuse me if I missed something there, but just had to ask. Good luck on this amp and I bet you nail it soon!

I was thinking the same thing but I never go full voltage until I go through dim bulb test stage first... However, I think there are times that full voltage will blow something up that a lamp bulb tester might not...? In that case maybe those parts are now out of the way once replaced, but if those parts are ones you just replaced... Well then S happens...

Geoffb have you been using a light bulb limiter at all?

Yeah I almost thought the Stage 100-160 was the right schematic too...   

I think if I was wanting this schematic to work on this amp I would divert my attention to this web page here...

http://www.fender.com/support/articles/fender-guitar-and-bass-amplifiers-owners-manuals-and-schematics-hard-copy-archives