Quote from: edjohansson on November 19, 2017, 07:51:28 PMAs I am a noob, I want to be sure I'm testing right.....do I put the black end of the multitester to the chassis ground and the red on the metal part?

To add to the great advice just given by Phatt and to answer your question...

Yes you would attach black lead of the meter to the chassis ground and then probe the red secondary connection points. There is the Red w/ Yellow stripe on the secondary and that is what we call the center tap. With amp off do a test to check for continuity from the chassis ground to the center tap connection. Also check resistance from the center tap to each end of the red secondary terminals.

Not saying all this as directive for response in trying to figure anything specific out. Actually just putting it out there so you can spend extra time learning it a bit, as those are thing I did that helped me understand it better too.

Not quite sure how you went about running signal from the Yamaha into the Fender? Just hope you did not plug speaker output from Yamaha amp into any of the inputs of the Fender. Probably you just sent line out signal into the power amp in on the Fender but just have to put it out there.

Blowing fuses is not good. Of course double check the right value of the fuse as solderdripper suggests. However, I think you need to be cautious going forward and even research how to make a light bulb limiter. This will prevent the amp from blowing fuses again and give you the ability to trouble shoot the amp.
https://www.ssguitar.com/index.php?topic=2093.0

At this point the hum you heard could have been DC voltage present on the speaker output. Do not connect a speaker to the amp until you know that there is 0v DC on the speaker terminal connections. If you put in a new fuse and it does not blow then measure DC voltage with your meter on the speaker terminals, again no speaker connected. If the fuse blows right away again then build the Light Bulb Limiter to proceed with the repair.

Do all as Enzo said...

Also if you still have those mosfets you removed test them with a meter to make sure they were faulty, then at least it confirms that part. When changing out the output transistors due to output transistors failure it is a good idea to replace the driver transistors for the outputs. First time powering up an amp, with such a repair, it is good practice to use a light bulb limiter or current monitoring variac to make sure we don't fry the outputs or something else.

Quote from: J M Fahey on September 15, 2017, 08:59:02 PMAlthough I´d personally send that back to Fender and ask for a refund, since they can´t make it work. Period.

Yeah no doubt!! Crazy that they make these amps like this now a days!!

Quote from: Keijo on August 23, 2017, 07:31:38 AMOne time I found 2 diodes in one amp that were both open. But I didn't need a DMM to find that out.  :duh

That's like hitting the Jackpot right there!!

I can't actually recall a time that I ever found an open diode. Plenty of shorted ones but never open.

Here is the service manual and the 17-11 board is pg18-19. Not sure this the one you are searching for...??

Edit: Well looking closer this one says 1971 and the one I think your looking for is for 1972 and later generation 2 or something. I will keep a look out for anything on the matter.

Better yet. Download Gimp image editor and save your jpg (image) files in formats that are small enough to upload to the actual SSguitar.com web server. I get tired of 3rd party hosting sites where someone even deletes linked files or forgot about the account, which they disappear.

Try this one out...

Quote from: Erich on August 12, 2017, 02:38:17 PMThe board in the one I have has 10 different spade terminals in the area where the power supply hooks up and none of them are marked with a color / voltage

Oh yeah Enzo I am with you 100%. I know those amps pretty well and they are clearly marked with P3, P4, and P5. I only requested a picture as the OP was almost implying that there are no markings on the board or something. Of course they are not marked with a color or voltage and that does not mean he said they are not marked with a P3 or other designators. However, he never even acknowledged that input. It's almost as if Erich thought Red and Red/Yellow on the board but those are just the color of the wires.

Quote from: Erich on August 12, 2017, 02:38:17 PMHey, I think I may have found he problem: The transformer outputs look like they have been hooked up wrong. I've checked the schematic I have and I can't tell from it (it's a crappy copy and I can't find another one) if the Xformer leads are attached to the board correctly. Does anyone have a picture of the fully connected board / power supply?

But to look at a picture of his amp we all could tell him right away if the transformer is connected correctly.

Quote from: Erich on August 12, 2017, 02:38:17 PM
The board in the one I have has 10 different spade terminals in the area where the power supply hooks up and none of them are marked with a color / voltage

I think we need a picture to understand better what you are looking at.

Well don't hold me to this completely, but this is where my search took me. I found this link here>>>
http://soundelectronic.ch/shop/index.php?main_page=product_info&cPath=4_37&products_id=493&zenid=pq7k3lmfpdchjng85hu8kfv526

At that point it confirmed B79-1 and it showed Model: 657179. It even had that it was made by Wulitzer. Which I think just means that Model: 657179 relates to Wulitzer. At least it shows something that might help you figure this out, good luck.

No. Reversing neutral and hot plugs on the amp will not make any REAL difference in this case. The safety ground being removed just means if there is leakage somewhere in the amp, to ground, the primary path will now only be the possibly grounded human guitar player. 

Stop trying to make a theory of what happened exactly. There are trained pros in the business of repair that can't EXACTLY tell you a WHICH transistor finally died when an amp suffered a major failure.

Edit: Just divide and conquer. Troubleshoot the amp by looking for obviously bad parts and replace. Test things (Transistors, Diodes, etc) in circuit with meter and see what might be bad. If a capacitor has started bulging then it is time to replace that guy.

Yeah it does look like something nasty sticky fell in the amp. Try using a q-tip and some 99% isopropyl alcohol to give it a good cleaning. That 220uf electrolytic cap needs to go on a diet his body broke right out of his outfit.  :lmao:

Try this out. It seems Digikey is now my go to for Sanken type transistors.

https://www.digikey.com/products/en?keywords=2sa1294

https://www.digikey.com/products/en?keywords=2sc3263