Blackstar S1 200 will not power on-all fuses OK...

[racerevlon]

Any thoughts? Amp belongs to a friend who told me this:

Power tubes showed signs of going bad and output tube fuse was blowing. Replaced the power tubes with a similarly - rated, matched quad. Now amp won't even power up.

This is where I got involved.

I can measure 117V all the way to the "CON1" molex connector on the main circuit board after which I would have to further disassemble the amp to continue tracing.

Flip the main power switch and literally nothing happens. Have checked Mains fuse, H.T. fuse, and output tube fuse -- all good. Checked all three internal fuses -- all good.

How can I test the actual power switch? What would cause the amp to do literally nothing when turned on?

Anyone have a schematic for the Blackstar Series One 200?

Thanks!

 

[mboogman]

The power switch should be pretty easy to check. Flip the switch to the on position (unplugged) and check to see if you've got continuity between the two switch poles.

 

[racerevlon]

Switch is good -- got power all the way to the HT fuse... Past that I have to really disassemble...

 

[mboogman]

Are the filament heaters working? That would be the next place I'd check. You should be getting something (6 VAC or so??) across pins 4/5 and 9 of the preamp tubes.

Obvious disclaimer: Be careful!

 

[racerevlon]

Nope--filament heaters don't appear to be getting power.

 

[TeleBlaster]

Ouch - starting to look like the supply transformer.

 

[mboogman]

Ouch - starting to look like the supply transformer.

Yep.

The heaters should be coming straight off the power transformer. Not knowing that amp, there is a possibility of there being a resistor or cap or something gone bad on the filament supply, but I'm not sure why you would need it.