Need Help with 5150-III 50W channel switching problem

[kka]

Hello,

I've got one on the bench and only ch1 (green) works. When engaging the manual switch for ch1/2 or ch3 on front panel it does not switch channels.

The +-15V supply is functioning. On page 4 of schematics I can measure the +15V at R21 and R38. When I press in the ch1/2 manual switch I get +5V on R203 (below R21 on schem) and same for R204 for ch3 switch pressed in.

I'd appreciate some help trouble shooting this issue. Thank you !

[Enzo]

So that stuff is OK, you can check to make sure that 15/5 thing gets all the way to pins 4 and 24 of the IC. The IC interprets those inputs and controls the relay drives to the right.

Is the +5v present on that board? On the IC? If it has 5v and those inputs, I'd expect a good IC to output control signals to the drives.

[kka]

So that stuff is OK, you can check to make sure that 15/5 thing gets all the way to pins 4 and 24 of the IC. The IC interprets those inputs and controls the relay drives to the right.

Is the +5v present on that board? On the IC? If it has 5v and those inputs, I'd expect a good IC to output control signals to the drives.

Thanks Enzo. The IC gets the 5V. I noticed that the 7805 gets really hot and after a short time the 5V output drop to 2-3V. If I disconnect 1 leg of R185 and R189 (to right of IC on schem) it's back to 5V. I will replace Q11 and Q10.

Q7 doesn't have the -15V coming from R108, it is +15V. So I'm replacing Q7 as well. I also noticed that the Ch1/2 muting JFET "Q2" (1st page of schem, off V5a grid) is fried and would shunt the signal to ground even when ch1/2 is selected. Must be connected to the ch. switching problem.

That Q2 is a J113. I only have a J112 in stock right now, can I use it instead? Thanks for the help !

[drewl]

Google the j112 and 113 PDF specs and they will tell you what each FET is and their specs.

[kka]

I found out that the IC "U8" is the problem. The 7805 got very hot and I traced it down to pin# 28 of U8 being shorted to Ground. Pin 28 is directly connected to the 7805. So U8 needs to be replaced. It is a "CY8C27443" . My question is can I purchase it from a 3rd party vendor like Mouse and replace it or do I need to get it from Fender if it must be programmed?

Thanks again for the help.

[g1]

I'm assuming you lifted pin 28 of U8 and the 7805 no longer got hot?
Otherwise, there are other things that run off the +5V line that could be the problem, how did you narrow it down to U8 ?

[kka]

Yes correct I lifted pin 28 and this pin lifted is shorted to ground and the 7805 no longer became hot. I had also one sidedly lifted All resistors connected to the 7805 and pin 28 was the last thing I checked.

[g1]

As this is a programmable IC, I think you will need to get it from Fender. I guess it is just for doing all the channel switching?

[J M Fahey]

Well done Fender !!!!!

You've turned a robust and mature classic Technology piece of equipment (tube based !!!!!) into a XXIst Century disposable piece of digital junk.

Which is what this amp will become if some day Ic8 ever fails and an original Factory programmed piece isn't available any more (3 ... 5 years?)

Of course, even if you are outside USA and manage to get one locally, it still will be a blank piece of plastic.

[Leo_Gnardo]

Well done Fender !!!!!

You've turned a robust and mature classic Technology piece of equipment (tube based !!!!!) into a XXIst Century disposable piece of digital junk.

Which is what this amp will become if some day Ic8 ever fails and an original Factory programmed piece isn't available any more (3 ... 5 years?)

Of course, even if you are outside USA and manage to get one locally, it still will be a blank piece of plastic.

Gotta "think outside the box" here. I'll bet the geniuses at Volkswagen can supply you an EPROM that will not only work but juice up your deflicted Fender and give it unexpected capabilities besides.

But seriously folks, I can't think of a better way to make a piece of equipment "proprietary". Juan's right, thanks Fender, for mediocrity guaranteed to last a . . . well a while anyway. What would Leo do. Leo Fender that is. Never this.

[MarkusBass]

Have you tried contacting the Consumer Relations Department listed here: http://www.evhgear.com/en-PL/support/ to get either programmed processor, or the program (and you will do the programming)? They should be able to provide it. I wonder if you can download it from another amp (if you gain access to it).
Also make sure that the track from pin #28 is not shorted elsewhere on the board. You said that 7805 was getting hot but not the processor.

Mark

[Enzo]

He did say the lifted pin was shorted to ground.

COme on, let's be fair. Fender put in this computer chip circuit because the amp is MIDI capable, you can control it from a MIDI control line. That requires a processor. If they wanted to just handle stomp switches, they would have made it a lot simpler like their other amps.

[kka]

I just wanted to update that Fender had sent me (free of charge) a programmed IC and after I installed it the channel switching worked perfectly again.

[drewl]

I just wanted to update that Fender had sent me (free of charge) a programmed IC and after I installed it the channel switching worked perfectly again.

Nice, thanks.
Gotta' remember that as I have a few customers with these.