Ampeg BA300-210 sound coming on and off

[Tubegamblar]

Hi, recently posted a mess of a thread so I reopen it again.

I do have to repair an Ampeg BA300-210. The amp was brought to me after passing by an "official" Ampeg Tech service. They told the customer to change the Power Amp PCB but they didn't have acces to the PCB or specified part. Customer calls me and requested a repair without changing this PCB as the "official Tech service" told him the power amp Mosfets where blown up.

As soon as I catch the amp I took off the Mosfets and they where all allright. Anyway I ordered some more (like 10) to match them and change them if it's going to be necessary.

Simptoms: The amp turns on, and remains on all the time. The sound is coming on for about a second and then shuts for about 5 seconds. This behavior repeats and is always the same cadence. 5 seconds shut and 1 second sound aprox.

I do have the schematic already as I'm repairing "a lot" of the same batch amps recently.... SAD... so I do know where to get the schems from Ampeg.

Thanks for your help. ;D

[DrGonz78]

Please post the schematic to this thread. That way other's here will be able to help without searching for it. Plus there is always a chance that we don't find the "Exact" version that you are referencing.

[Tubegamblar]

Here it goes:

http://ge.tt/6feKikh2

[J M Fahey]

Thanks for posting.
That said, if you have the full schematic (preamp/supply/etc.) please also post it here, it can help others in the future.
AND ....... you might very well have a power supply problem.

First thngs first: check that you get your +/-42V rails.
An overloaded SMPS usually does that: puts out voltage, senses voltage and current and if it detects a problem self shuts off.

Since there are also speaker out DC sensors, any DC there will also turn amp off.

As usual, work with no speakers or any other load attached.

Just in case, build a lamp bulb limiter, although many SMPS are very fussy about voltage and self turn off if they don´t like what they get.

[Tubegamblar]

Thanks for posting.
That said, if you have the full schematic (preamp/supply/etc.) please also post it here, it can help others in the future.
AND ....... you might very well have a power supply problem.

First thngs first: check that you get your +/-42V rails.
An overloaded SMPS usually does that: puts out voltage, senses voltage and current and if it detects a problem self shuts off.

Since there are also speaker out DC sensors, any DC there will also turn amp off.

As usual, work with no speakers or any other load attached.

Just in case, build a lamp bulb limiter, although many SMPS are very fussy about voltage and self turn off if they don´t like what they get.

Thankyou Juanma,

I do have a Bulb limiter I always use it. ;D As soon as I have the full schem I'm posting it. Tomorrow morning i'm checking out these voltages and guessing things out so Thanks again.

[Tubegamblar]

Well I'm reading 30.37volts, directly measured from the connector J6 to the poweramp board. Any more ideas? I can check

[Tubegamblar]

Full Schem here:

Seems like all the voltages are correct from the power supply as told in the schematic...

[Tubegamblar]

Still working on it but I don't find the damn failiure... any suggestion anyone?

[J M Fahey]

Ok, just downloaded the schematic and will study it later, now surrounded by Musicians who have the funny notion thatbthey *must* play tonight

What´s so special about Friday and Saturday night?
Why can´t they just play, say, on Tuesday 10 AM or something normal?

Just as an advance, it IS a complex Class D amp, a complex switching supply, amp is chock full of self protecting circuits which will turn it off for about *anything* so we´ll try but nothing can be promised.Plus it must certainly be full of small SMD parts.

"Anything can be repaired" of course, at least in theory ... hope amp read the same book

[Tubegamblar]

SO many Thanks Faheyman,

I'm doing my homework also.... maybe the bell sounds, but if not at least we tried!

[Jazz P Bass]

Seeing that this amp uses an SMPS, I would suggest that you do not use a lamp limiter for testing.

And remove the load on the output.