Fender Jazzmaster Ultralight

[schraedertr]

I have a Fender Jazzmaster Ultralight that won't turn on. They have a power amp /DSP board with surface mount components including the low voltage regulators. I have 40VDC output from the power supply to the power amp board. I unplugged the preamp boards from the power amp board and measured the low voltage supply voltages.

The -15VDC supply is good, but I'm getting only 2 VDC at the output of the 7815 and 7912 regulators. The 5VDC supply also reads only 2V and comes from it's own transformer windings according to Page 2 of the schematic:

http://support.fender.com/schematics...ight_59000.pdf

So now what? See if Fender sells the board complete? Removed the power transistors and see if one is shorted? They are mounted to the underside of the extruded aluminum chassis top behind the power supply board.

I guess I'm looking for advice whether to abandon the quest (don't have the capability to work on surface mount boards), buy a replacement board if Fender has any, or dig deeper into the power amp.

Thanks

[schraedertr]

Update: I looked for abnormal resistance across the output transistors and definately found a diffference between the Q1 readings and everything else. The output transistors are mounted on an aluminum heat sink that screws through a galvanized cage into the case top. The cage has 16 tabs that are soldered to the rear of the board. The transistors cannot be removed individually, all 8 have to come off with the heat sink. Anyway, it's all apart and my cheap transistor tester shows no problem with any of them.

I'm back to buy a board or can it, I guess.

[Jazz P Bass]

The good news is the main SMPS power supply is working.
(seems to be missing from the schematic)
The +15, -15 & 5v is supplied by a secondary switcher power supply.
It is labeled Low Voltage Supply.
I find it odd that you have -15Vdc & +15 / 5volt supplies are low.
It may be that something is loading them down.
Is there a connector on the LV supply that you can disconnect from everything else to see if the voltages correct themselves.
(this amp looks like a nightmare)

[Tony335]

My 5 year old Fender Jazzmaster Ultralight went "belly-up" two weeks ago. My local amp tech says it needs a new power supply PCB (part no. 007 0101 000). This part costs £290 (€360 or $420) but I can't get it from Fender UK or from Fender in Scottsdale. I'm told this is "surface mounted" technology and as such cannot be repaired! Iwas really fond of that little amp (especially when a gig was upstairs) and now I'm dragging my MarkIII Boogie to every gig. Does anyone know if this amp is repairable???

[Jazz P Bass]

What your tech is saying is "I cannot handle surface mount technology".
From lack of skill, equipment, desire...
Who knows?
The power supply is most assuredly repairable, if the circuit board is in sound shape.

[Tony335]

JPB, that is really good news. My guitar tech is a nice guy and is expert on tube amps. Maybe, as you suggest, I need to look further. I'm grateful for your input and I'll post the results. Thanks.