Repairing Fender Frontman 15R

[Renegadrian]

Hi, i just acquired for cheap a dead frontman 15r. only the reverb tank would cover its cost...
I was hoping in a dead fuse, or a protection diode, but nope, tried the installed fuse and the spare it has in the socket but still doesn't turn on. It seems I have no voltage at the trannie output. Tried to read ac voltage but 0 all the way.
Given the low value of the amp, I don't want to spend loads of money for a spar, if needs be. I have no indication on the trannie itself, from the schematic I got I read it's a 16.4v-0-16-4v.
Would a 15-0-15 be enough?! How many watts or VA are needed?! would a toroidal or an encloded or open trannie like the hahn work?! https://www.tme.eu/it/details/v50103/trasformatori-per-pcb/hahn/ or something like that LINK

EDIT: AMP SCHEMATIC for reference

[PRR]

That Hahn says "5W" in the small print.

A "Frontman 15" might imply 15 Watts out? With losses, this is a 25W-30W load on the transformer.

Which you might guess by comparing size/weight of the stock iron against possible replacements. (I took the 600 pound engine out of my Jeep; I did not replace it with a 150 pound lawn-tractor engine.)

But back up. Don't keep burning fuses. Build a Dim Lamp Tester. If the amp appears "shorted", start disconnecting stuff inside. A shorted cap or rectifier is "a short", but if disconnecting the rectifier/cap leaving only the PT and line wiring "un-shorts it" then you have A Clue. (Or it could be the power amp downstream from the rect/cap.....)

[Renegadrian]

Desoldered the 3 wires coming out of the PT - they shoud read 16.4v-0-16-4v but I got no voltage...So I think the PT is dead...I should try a spare one...

[PRR]

Are there any Ohms in it?

[Renegadrian]

Are there any Ohms in it?

3.9 ohms between black (0) and either v wire

[Kevin Mitchell]

Oh man. I have my old F15 from middle school (about 15 years ago!) kicking around. That thing would pick up radio frequencies until I smacked the plate connecting the handle to the cabinet. Weird little mariachi & jesus music playing monster.

It's in pieces for I have the tendency to tare things apart when they give me problems. I learned I could some-what easily convert it to a 15R since they use the same boards and chassis. I think someone on the web had already done this. Though it's always been more trouble than it was worth just to use it outside of the bedroom.

What I'm getting at is... I have parts available. Can't recall if the PT is different it's been a while since I reviewed the schematics though your description sounds about right.

-EDIT
You probably need an export PT, huh? 

[thermionix]

Are there any Ohms in it?

3.9 ohms between black (0) and either v wire

Primary open?

[Renegadrian]

Are there any Ohms in it?

3.9 ohms between black (0) and either v wire

Primary open?

Primary still connected to power switch and fused power in, power cable not inserted and switch turned off (so the 2 primary wires end at the switch)

[amptramp]

Have you measured the resistance of the transformer primary?  If it is OK and your secondaries are OK, the transformer should be OK.  The power switch is often loaded up with oxide on the contacts and this should be checked for on/off resistance.  If you have a death cap, remove it and see if it works.  Measure from power plug pin to pin but be aware that corrosion may make a good measurement look open.

[Renegadrian]

-EDIT
You probably need an export PT, huh? 

Yes I do, but thx for the offer!!!

[Renegadrian]

Have you measured the resistance of the transformer primary?  If it is OK and your secondaries are OK, the transformer should be OK.  The power switch is often loaded up with oxide on the contacts and this should be checked for on/off resistance.  If you have a death cap, remove it and see if it works.  Measure from power plug pin to pin but be aware that corrosion may make a good measurement look open.

please explain better how to measure resistance. power switch is good, no oxide, I measured voltages, it has one job and does it perfectly.

[thermionix]

If your switch and fuse are known to be good, you can read across the two mains prongs on the power cord, or on the IEC connector if it has a detachable cord (power switch ON, not plugged in obviously).  But since you already have the chassis out, you can read the two primary leads directly.  Yellow and black wires on the power switch, per the schematic.  If it's good, should be low ohms, maybe around 200.  If you get infinite resistance (open), it's bad.  Some PTs have an internal fuse on the primary.

[PRR]

I'd expect the primary to be 10 ohms not 200.

But the usual choices are "zero" (<1r), "few/some", or "infinite".

[thermionix]

Nothing similar here to measure, all my amp PTs are for tube amps.  I grabbed a random wall wart and another low voltage PT and they were in the 120-200r range.  I figured bigger wire for a 15W amp, but more turns for euro voltage, so maybe some similar number.  But yeah, you don't want to see 10s of Ks, rather some "low" resistance.  I should have been more specific about how rough my estimate was.

[Renegadrian]

Got no ohms on the primary - I said, heck I got another small amp like this (marshall valvestate 15w) amp turned on but tda 2050 power amp just exploded...

[thermionix]

Got no ohms on the primary

Zero ohms or no reading?

[Renegadrian]

Finally got a new transformer from aliexpress - worth the wait, that and a fresh 2050 and it's like new.