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JBL Eon, ping Phil

Phil Allison,

a while ago I believe you posted about a peculiar trait in (SMPS) JBL Eon amps, whereby you can't run them up on a Variac safely. Since then I've had 2 powered satellites and a powered sub where I noticed the same thing.

I had the sub in today and replaced a blown bridge rectifier. I was fairly sure the power amp was OK, no shorted devices, and a blown amp is unlikely to take out the bridge.

I usually check these things with a Variac and 100W lightbulb in series, and sure enough in all 3 cases it looked like excessive current draw at a fairly low voltage, so stop things right there.

So I tried the repaired sub today on 240v with the lightbulb and it was clear that the excessive current was going to continue. However, on disconnection from the mains, both power supply rails held indefinitely at around + and - 25v, indicating there was probably no short in the power amp.

Much as I hated to do so, my only option was then to just connect the device to the mains and turn it on, and it didn't blow up and is now back with the customer.

I think this was something to do with a soft start relay not kicking in unless the full supply voltage is used, but can't quite figure out how that would work in practice.

Maybe you could remind us? I don't have schematics for these things.

Cheers,

Gareth.

Reply to
Gareth Magennis
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That kinda rings a bell. Also, in working on TVs which all have switched mo de power supplies now, you usually can't use a variac.

How to try to keep the smoke in ? I have thought of that and the answer mig ht be to remove the main filter off the line recifiers. Temporarily replace it with about a 33 uF. Then a modded light bulb tester, like with two high er wattage bulbs in parallel.

With some timkering you can probably find some comfortable values that'll a llow the circuit to power up fairly normally but yet keep the fire brigade away.

I remember a certain model of Sony TV, didn't have a switch mode but it use d a startup cap from the main B+ down to about a 20 vlt source to run the h orizontal osxcillator which was then powered off the flyback. No way to sta rt those on a variac either. Also Zeniths that had the A-11345 startup modu le would not slow start. I'm pretty sure RCAs from CTC 88 through 92 wouldn 't either.

I don't like it when manufacturers do that but whaddya gonna do ?

Well I know what we're going to do, outsmartem and fix their shit so they d on't sell more of it ! LOL

Reply to
jurb6006

That kinda rings a bell. Also, in working on TVs which all have switched mode power supplies now, you usually can't use a variac.

How to try to keep the smoke in ? I have thought of that and the answer might be to remove the main filter off the line recifiers. Temporarily replace it with about a 33 uF. Then a modded light bulb tester, like with two higher wattage bulbs in parallel.

With some timkering you can probably find some comfortable values that'll allow the circuit to power up fairly normally but yet keep the fire brigade away.

I remember a certain model of Sony TV, didn't have a switch mode but it used a startup cap from the main B+ down to about a 20 vlt source to run the horizontal osxcillator which was then powered off the flyback. No way to start those on a variac either. Also Zeniths that had the A-11345 startup module would not slow start. I'm pretty sure RCAs from CTC 88 through 92 wouldn't either.

I don't like it when manufacturers do that but whaddya gonna do ?

Well I know what we're going to do, outsmartem and fix their shit so they don't sell more of it ! LOL

I really don't like SMPS's because I don't know enough about them, I am way out of my comfort zone here.

But, most modern audio equipment (I only know audio equipment) using SMPS's use small IC's as the controller, which are designed to tolerate almost anything thrown at it. They will only attempt to power up once they have enough voltage to do so, and will shut down if excessive current draw occurs, without destroying anything.

You can usually power them up with a Variac and lightbulb, but with the JBL's you can't, because I believe they have added some relay circuitry that makes this not possible. I'd just like to know what that is.

Gareth.

Reply to
Gareth Magennis

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