Ampeg Portaflex PF-500 on the bench, waiting for service manual from Ampeg

[vertamps]

Hello, started to dig into a customers PF-500.
I could only find the two sheet power supply schematic online, not the full service manual yet.

So far iv checked that the 'U7 555 ic output pin is high at 3.8v causing U5 to be in shutdown mode so the +82/-82 switch mode generated voltages are not present.
The 'T4 temperature switch is fine, normally closed.

I will be working my may backwards through 'U6.
Seems there engineers made this bass amp over complicated, just not used to it.

Would be nice to have a non-grounded oscilloscope for this isolated high voltage supply, glad i have a breaker outlet. I know i could use a two prong extension cord, not gonna do it.

[nickb]

Power supply: Here ya go, bro..

[vertamps]

I already had those schematics, turns out those are all i needed. The Power_mute was low causing Q3 to turn on and the trigger pin 2 of 'U3 555 timer to sit at 1.1v. I checked the power mosfets and Q11 is shorted, Q10 is fine. I didn't think to check the output as i got sucked in to understanding how this circuit worked.

So why did the Mosfet short? I will check surround circuit, mayby even order the classD driver ic just incase with the Mosfets.

[nickb]

I had read your OP as 'I have sheet two" instead of what you actually said. Oh well. I tried..


If is a customer's unit I'd replace both MOSFETS. It's cheap insurance. Why did it blow? We can only speculate.

[vertamps]

I made a mistake, and blew U1, the driver ic.

I pulled the Q11 shorted Mosfet and turned the unit on. The fault light went off. Turned it off and back on same thing but this was a bad idea. R101 the 4.7 ohm resistor blew open from to much current being drawn by the now blown U1 driver IC... which also destroyed a within spec test mosfet soldered in. Totally my fault.

[Alex R]

i always seem end up blowing something in those damn things. Fiddly.

[Chuckssr]

Hello new here at music electronics forms. I ran across the site on
a Google search for schematic for PF 500.

The PF 500 I have, has a ASSY: 2034544-01 REV D00.
I also had no luck at loud technologies for schematics.

I found REV J03 schematic, it shows buffer transistors for Q 10 and Q11. And in the
REV list indicates REV D00 added Snubbers to Q10 and Q11.

Then a came here, and thank you nickb for the REV C02!
And thank you vertamps for starting this thread!

My PF 500, Fault LED on at power up, stays on. No output.
Low supply comes up.
Pulled it apart, test Q10 and Q11 in circuit. Q10 dead short, unscrewed TS1,
pulled Q10 and Q11 tied to the heat sink,
Used a DMM diode mode Q10=short, Q11= on acting right
but not a short. Found snubber R41= open, it look like it got
pretty hot. Have not found any other shorts on the factory
Fresh PCB.

Will replace Q10, Q11, snubber R41, C3, R45, C15.
Then see if it comes back alive.

Uh Oh, pulled the clamp bar off Q10 and Q11, they are not
IRFB4227s, they are FDP33N25s!

Oh well, I will replace with IRFB4227s. Snubber C3 and C15
will be 47pF as changed in REV E01.

[Tubegamblar]

Have you had any luck? tell us

Thanks

[francophone]

Ampeg PF-500

Have you had any luck? tell us

Thanks

Any results for this? Does anyone have schematics or description for the changes between Rev C and Rev J? Very interested.

[MojoAmpGuy]

What values are snubber resistors R41 & R45?

I can't find values for snubber resistors R41 & R45 on my version of the schematic. I have very similar circumstances. Burnt out snubber components. Q10 open , Q11 appears ok but might swop out to be safe.

Not sure I understand how the power mute circuit around Q3 & Q8 should work when healthy. Can anyone clarify. Thanks

Hello new here at music electronics forms. I ran across the site on
a Google search for schematic for PF 500.

The PF 500 I have, has a ASSY: 2034544-01 REV D00.
I also had no luck at loud technologies for schematics.

I found REV J03 schematic, it shows buffer transistors for Q 10 and Q11. And in the
REV list indicates REV D00 added Snubbers to Q10 and Q11.

Then a came here, and thank you nickb for the REV C02!
And thank you vertamps for starting this thread!

My PF 500, Fault LED on at power up, stays on. No output.
Low supply comes up.
Pulled it apart, test Q10 and Q11 in circuit. Q10 dead short, unscrewed TS1,
pulled Q10 and Q11 tied to the heat sink,
Used a DMM diode mode Q10=short, Q11= on acting right
but not a short. Found snubber R41= open, it look like it got
pretty hot. Have not found any other shorts on the factory
Fresh PCB.

Will replace Q10, Q11, snubber R41, C3, R45, C15.
Then see if it comes back alive.

Uh Oh, pulled the clamp bar off Q10 and Q11, they are not
IRFB4227s, they are FDP33N25s!

Oh well, I will replace with IRFB4227s. Snubber C3 and C15
will be 47pF as changed in REV E01.

[Ronny Schmauser]

Hello!
Has anyone the schematic for the preamp?
The transformer of the tonestack fell out and i have trouble putting it in the right way.
I tested several directions but im not sure if theres another fault because the mid-switch is partly working in some directions(of the transformer wiring).

thanks!

[Enzo]

The inductor is square with one angled corner, yes? That angled corner points to the front panel and the push switch, so it aims between the switch and P3.

[mothbox]

I'm interested in getting the latest (J02?) schematic if anyone has it. I'd like to know the changes made to the mainboard so I can assess whether it's an easy job to modify mine or if I will need to buy the latest board and do a full replacement.

From what I've read there is a general issue with the input overloading a part of the circuit and the amp shuts down and gives the fault light. I'm getting this symptom.

[alansombr]

hola boa noite
meu amplificador ampeg pf500 ,demora muito para ligar
apos ligar o botao ele leva 50 ou 65 segundos para ligar