need advice before powering up amps from storage

[cyclecamper]

I have 4 very large Soundcraftsmen PR1800 professional stereo power amps that haven't been powered up in at least 6 years, some of them probably longer (2 haven't been tested since I acquired them 6 years ago from an estate sale; all worked last time used but can't date that event). They have switching power supplies and rather conventional analog audio amp sections with balanced inputs and FET outputs.

If these were conventional power supplies, I would power them up slowly on a variable transformer, just to be gentle to the big power supply filter caps. But these are regulated switching power supplies. I hear that these have a reputation for their power supply caps blowing their vents and sometimes causing subsequent damage to the power supply SCRs or something. Any advice? Should I put a big resistor in series with the caps the first time I turn one on, so it charges them up more slowly? What's my real risk? Should I just go for it? The longer I wait, the more I hesitate.

[smartx21]

What about trying a series incandescent light bulb?
I think one huge of these old fellows would help, in order to avoid unwanted oscillations.
All the best,
Max.

[Nrik]

Just power them on.
They are probably equipped with a lot of safety circuits and fuses, and unless they have been stored in a super-moisty place, there is no reason to believe they should fail at all.

16 years ago I build a THE END amplifier, and it too had been standing in my basement for 5-6 years. Recently I powered it and it worked perfectly, and I have used it in my system since. And that is a DIY amp, build as my first experince into DIY electronic - imagine the difference to a full-blown proff-amp: No risk at all.

[jaycee]

Personally i'd use the bulb just in case. If something DOES go wrong, the bulb will light, and fireworks will be avoided

[Nrik]

Switch supplys may fail if the caps are of too low value. But the only consequence will be no voltage out. So again: just plug them in and see what happens.

[cyclecamper]

Thanks. I think I'll just "go for it" and hope for the best.

[Xoc1]

Plug in with nothing connected & volume controls set to minimum on the amp & check the outputs for DC offsets.
If you have the equipment, maybe try some tests with a dummy load, scope & frequency generator.
Check the full output waveform off load, and then with a dummy load. This should at least reassure you that the amplifiers are basically functioning as they should, before you connect your speakers.

[Nrik]

Originally Posted by Xoc1

Plug in with nothing connected & volume controls set to minimum on the amp & check the outputs for DC offsets.
If you have the equipment, maybe try some tests with a dummy load, scope & frequency generator.
Check the full output waveform off load, and then with a dummy load. This should at least reassure you that the amplifiers are basically functioning as they should, before you connect your speakers.

agree

[cyclecamper]

For a first test I'll probably connect a single driver I'm not concerned about. That's enough for a go/nogo test and to power up the power supply. I'm not worried about he amplifier sections, just the power supply caps. The PWM switching poser supply delivers incredible initial current when you first turn these on.

[Nrik]

So...what happened?
Any explosions?