Aw poop! PL400 fried!

[MarkWComer]

Pull one end of D9 or D10 on the affected channel and see if it stops then...that eliminates the protection circuit....

Disable the SOA protection circuit first. Lift one end of D9 and D10 on each channel.

D10L is just above the "burn hole."

Thanks- will do, but will have to get to it tomorrow...

Will let you know, but... I do want the SOA circuit to be active, correct? Eventually replace those diodes, I assume (if that kills the fault?).

 

[laatsch55]

Or the 1304, 1305 pair....

 

[MarkWComer]

Or the 1304, 1305 pair....

Both of those were replaced with new ones. Will yank the diodes first. Although they've been replaced there's really no guarantee that they're perfectly good.

 

[laatsch55]

There's more to the protection circuit than those components, pulling one end of D9 or D10 isolates the SOA circuit, then you can debug it...

 

[Gepetto]

D10L is just above the "burn hole."

Thanks- will do, but will have to get to it tomorrow...

Will let you know, but... I do want the SOA circuit to be active, correct? Eventually replace those diodes, I assume (if that kills the fault?).

It is unlikely that the diodes are the fault Mark. It is usually the circuit that is behind each of these diodes that is the cause of the fault. The SOA circuit works only when the output transistors are not faulted. In the event of a catastrophic failure of an output device as you experienced, the SOA circuit can no longer clamp the output transistors and the SOA circuit can become the victim of the failed output device.

 

[MarkWComer]

There's more to the protection circuit than those components, pulling one end of D9 or D10 isolates the SOA circuit, then you can debug it...

I assumed as much- the diodes and the 1304/1305 combo alone aren't the entire SOA circuit- they can't be.

It is unlikely that the diodes are the fault Mark. It is usually the circuit that is behind each of these diodes that is the cause of the fault. The SOA circuit works only when the output transistors are not faulted. In the event of a catastrophic failure of an output device as you experienced, the SOA circuit can no longer clamp the output transistors and the SOA circuit can become the victim of the failed output device.

That sheds a lot of understanding of what happened- the SOA burned out because what it protected burned out, a "co-dependant" failure, so disabling it (the SOA) would verify the fault. I just don't know which components comprise the SOA in order to check them.

 

[Gepetto]

I assumed as much- the diodes and the 1304/1305 combo alone aren't the entire SOA circuit- they can't be.



That sheds a lot of understanding of what happened- the SOA burned out because what it protected burned out, a "co-dependant" failure, so disabling it (the SOA) would verify the fault. I just don't know which components comprise the SOA in order to check them.

Top side
D9, Q8, D11, C14, R26, R27, R32, R24, R28, C15

Bottom side
D10, Q9, D12, C17, R31, R30, R33, R25, R29, C16

Most likely the semiconductors Mark.

 

[ElectronMan]

Smelling Ozone?

MarkWComer,

It appears you weren't kidding when your video depicted splatter coming from who knows where...

Mark if your laser-beam-eye can't fix it perhaps my electron-wrangler can herd your stray electrons back in the correct direction...I imagine something akin to herding cats.

Wish you the best,

Sign Charles Hammill aka ElectronMan

Post Script: MarkWComer thank you for the invite from your YouTube videos. This should be fun, making ozone amongst fellow sparkees ...lol

It's not real music until you play it on a Phase Linear Amplifier...

 

[MarkWComer]

Top side
D9, Q8, D11, C14, R26, R27, R32, R24, R28, C15

Bottom side
D10, Q9, D12, C17, R31, R30, R33, R25, R29, C16

Most likely the semiconductors Mark.

Thanks- I can isolate where to look, perhaps the replacement transistors were bad, even though bought as NOS.

Umm... shit... holidays come along and spoil all my fun! "Bring an appetizer to my party" means a few hours in the kitchen, dressing up in my best flannel shirt, etc. Frenzy, AKA "the headless chicken dance."

EDIT: Further evidence: Yup- the components you listed were the ones that were physically fried- and all part of the SOA circuit...

 

[MarkWComer]

It appears you weren't kidding when your video depicted splatter coming from who knows where...

Welcome to the zoo! User "Gepetto" (Joe) is the designer of the upgrade circuits and really knows his stuff, everyone else is also on top of their game here, too. Couldn't ask for a better forum, better group of members, or a better amp (spontaneous transistor spooges aside...).

I'm glad to be here!
​

 

[ElectronMan]

Welcome to the zoo! User "Gepetto" (Joe) is the designer of the upgrade circuits and really knows his stuff, everyone else is also on top of their game here, too. Couldn't ask for a better forum, better group of members, or a better amp (spontaneous transistor spooges aside...).

I'm glad to be here!
​

Glad I'm here too Thanks! Pleased to meet "Gepetto" (Joe). Good bunch, I'll try to behave ;P

 

[wattsabundant]

There's no reason to believe the relay board should have failed. The relay itself? Maybe. It's intended to be sacrificial and that's why it's in a socket.

As for the fuses, voltage rating is definitely important. The AGX 8 is not rate for DC and when used on a 80 VDC bus only serves to put out the fire. In this application, when the element melts, arcing occurs (which is why the glass turns black) and the fuse finally opens when everything inside the fuse burns up. When used in an AC circuit the fuse doesn't arc because the current goes to zero every half cycle and the fuse opens.

The same holds true for relays and switches. If you look at toggle switches and relays, the contact rating is typically 250VAC and 32VDC. All relays (costing under $100 each) including the ones I use in the relay boards are not rated to break 100VDC. The reason the relay board works is because it acts like a crowbar across the speaker at the same time it tries to disconnect the speaker from the blown amp. The commercial relay circuits in every amp and receiver I've seen only attempt to disconnect the speaker. The attached image shows the relay pulled from a failed Marantz 140. You can see where the contact welded and didn't likely protect the speaker.

 

[MarkWComer]

I'll try to behave ;P

You'd be the only one...

 

[MarkWComer]

There's no reason to believe the relay board should have failed. The relay itself? Maybe. It's intended to be sacrificial and that's why it's in a socket.

As for the fuses, voltage rating is definitely important. The AGX 8 is not rate for DC and when used on a 80 VDC bus only serves to put out the fire. In this application, when the element melts, arcing occurs (which is why the glass turns black) and the fuse finally opens when everything inside the fuse burns up. When used in an AC circuit the fuse doesn't arc because the current goes to zero every half cycle and the fuse opens.

The same holds true for relays and switches. If you look at toggle switches and relays, the contact rating is typically 250VAC and 32VDC. All relays (costing under $100 each) including the ones I use in the relay boards are not rated to break 100VDC. The reason the relay board works is because it acts like a crowbar across the speaker at the same time it tries to disconnect the speaker from the blown amp. The commercial relay circuits in every amp and receiver I've seen only attempt to disconnect the speaker. The attached image shows the relay pulled from a failed Marantz 140. You can see where the contact welded and didn't likely protect the speaker.

Thanks- good to know as well as being what I hoped it would do (it's also what I've been led to believe from your literature and circuit theory/description. The blown transistors show straight conductance and I thought that this may have fed straight 80v DC into the DCP and blown it apart. I have all the components to rebuild it for safety's sake sans the relay itself- which is what I probably should have bought. Knowing this is the expendable part tells me to make another order from Mouser! And thanks for the clue, all this stuff is good and usable knowledge.

Just czeching in here- I'm not willfully dragging my feet, but Christmas is more or less pulling me into too many directions. I'm also dealing with a chick in California undergoing a nervous breakdown- I'm worried about a possible suicide or at least a grievous self- injury. It seems that my life is not my own anymore...

 

[laatsch55]

To those of us who really care Mark, it rarely is....

 

[MarkWComer]

To those of us who really care Mark, it rarely is....

Just a catch-up:

• My sister is doing as well as can be expected- and is actually much better! My great-niece in Atlanta is mixing up cannabis oil with butter (so she doesn't have to smoke pot) and her appetite is greatly improved. Now on oxygen, some kind of stuff through a nebulizer, and getting home therapy. She hasn't had a cigarette since this episode started, I quit on the week of her hospital discharge.
• My great-niece (the other one- next door) had some seizures and I was expecting the worst, but it turned out to be convulsive syncope, somehow related to puberty (so I won't introduce her to cannabis until she's 21).
• SC has a medical cannabis bill that I support, so I'm visiting the State House trying to get support from legislators.

And a decision:
I'm gonna give up on the REV D driver board and order the REV E as soon as I can. Too many obsolete components, the "germanium twins" (2N1304/5) have been long obsolete and after looking through Digi-Key and Mouser I find that 2N3439 and 2N5416 are also obsolete. Sure, I can find them elsewhere, but having so many obsolete components in something that I enjoy so much is something I don't like- so new driver board (and new meters!) are on the horizon.

EDIT: Bought the transistors from eBay anyway, will get the board up and running, but still the idea of so many obsolete components bugs me too much.

 

[laatsch55]

I like your reasoning....

 

[MarkWComer]

Emitter resistors R41 and R46...

Running fine!

 

[laatsch55]

Coolness...