Samson D412 Powered Speaker Overheating

[jpglyde]

I have a Samson D412 Powered speaker on the bench which is overheating at idle... almost enough for shutdown but the slightest bit of music puts it over the edge. From what I've read, there is a bias problem with the MOSFET amp.

Can anyone share the schematics, bias procedure for these amps, or more preferably, the Service Bulletin issued by Samson which I can't access because I'm not a Samson service tech?

Thanks

Jason

[guitician]

It seems that there is a bias pot on those somewhere that drifts out of setting due to vibration. Look for it and see if moving it slightly in either direction gets some improvement. You could monitor the PS voltages while doing this too, as they will no doubt be going up with reduced loading.

[soundguruman]

If you have a variac, run it on 100 volts AC.
See if it still overheats.
That may provide a clue...may or may not.

There is certain equipment that is designed to run on 100 VAC.
It is relabeled 120 volt, and sold in the USA.
This type of equipment has a habit of running too hot.

You can usually get the schematics from Loud Technology, after signing a waver...

Some of these devices have power amp boards manufactured by Sanyo, Japan.
Open it up and have a look at the power amp board, and see if the label says: Sanyo.

Does the power amp module IC say: STK404-100?

Whoops sorry, PDF did not attach properly.
Will try another method.

Anyhow, Loud Technology sells Sanyo,
relabeld as Kustom, and Sampson, and other products.

This Sanyo Power amp is designed for 100 VAC.
When run on 120 volts, it runs too hot.
I have seen this in several products Loud Technology sells.

However, it can be modified...
and there are Sanyo service bulletins, that address the problems.

[MarkusBass]

Can you post a photo of the power amp board? It seems to me that this is class-D 400W amp and it has nothing to do with STK from Sanyo (which is class AB). I would also expect that there is a switching power supply.
Is it this one: http://www.samsontech.com/samson/pro...auro/aurod412/ ?

Mark

[jpglyde]

Mark, that is the correct speaker but it is a linear power supply.
MOSFETS are IRFP140N and IRFP9140N
Transistors are STD03N and STD03P

[km6xz]

I do not have the schematic but the suggestion of bias pot having shifted is a reasonable one. It appears to be a A/B amp for the LF and a chip for the HF amp. If the sound is ok, and there is no DC offset, look for bias tracking or bias pot problems. I can see a thermal tracking diode attached to the heatsink so at the base of those wires should be the bias circuit.
Disconnect the load until the problem is resolved. There are other possibilities including a high frequency oscillation in the LF amp when no signal is present. Running a just-under-clipping 1khz signal decrease the heat? Does it generate full power as expected into dummy loads?

[MarkusBass]

Thanks for the info. Unfortunately, the photos are too small to see the details. Could you make slightly bigger photos? Is there a trim-pot to set the quiescent current? You can measure a voltage drop on ballast resistors. It seems that the power amp is rather 200W and not 400W.

Mark

[jpglyde]

Thanks for the input. I took Guitician's advice and turned the bias pot down and watched the rails gain 2 or 3 volts. It resulted in about an 80% decrease in heat. I ran it pretty hard for a while and it never broke a sweat. I'm calling the customer and telling him to come get it.

[guitician]

Did you set some hot glue on the pot? Or, just replace it with some multi-turn trimmer that wont drift like that one did.

[J M Fahey]

There is certain equipment that is designed to run on 100 VAC.
It is relabeled 120 volt, and sold in the USA.
This type of equipment has a habit of running too hot.

Obsessions are hard to fight and are recurrent.

You can usually get the schematics from Loud Technology, after signing a waver...

Samson is unrelated to Loud Technologies.
.....
oh, I forgot, both sell Chinese made products so they are all the same.
Cunning devious Chinese
All Chinese companies are in fact run by Mao Tse Tung who is conquering the World.

Some of these devices have power amp boards manufactured by Sanyo, Japan.
Open it up and have a look at the power amp board, and see if the label says: Sanyo.

What if it does not?

Does the power amp module IC say: STK404-100?

I bet thatīs the only one you ever heard about.

Anyhow, Loud Technology sells Sanyo,
relabeld as Kustom, and Sampson, and other products.

Unrelated companies.

This Sanyo Power amp is designed for 100 VAC.
When run on 120 volts, it runs too hot.

Here we go again.

I have seen this in several products Loud Technology sells.

?????????????

This is a remainder of what we were daily subject to, just a couple months ago.

Why am I beating this dead horse?

To remind that besides the dozen or so regulars who post here all the time and which are the tip of the Iceberg, there is A TON of visitors which obviously reach here because of some search, read an answer to their problems and leave, without reading a later refutation of all this nonsense.

They may either take a bad decision, damage something, even get hurt or killed if they followed SGM dangerous advice on hot chassis or at least cut and paste and spread (even more) nonsense on the Net.

This particular one coming from (formerly) respected MEF !!!!

Itīs easy to check in the thread list, that for example this particular one had

Replies: 8
Views: 427

easy Math tells me that besides the "visible" 8 answers from just 4 members ..... thereīs 419 other guests who read this and may act on that.

And thatīs a constant on MEF.
Itīs much more read than apparent on first sight.

There lies the huge damage which can be made to MEF .

[Leo_Gnardo]

There lies the huge damage which can be made to MEF .

+1, the second biggest damage is the rest of the world will think we're all as kooky as SGM.

Still haven't seen any arching resistors on Mesa PC boards. Hey Archie, you seen any? You, Jughead? Veronica? Betty? Mister Weatherbee? Anybody?

FWIW Samson started and for all I know still is, a subdivision or spinoff of Sam Ash. Sam's Son. Had to find something for the kid to do, he's too old for the sandbox.

[ppros]

Helloy!
My name is Pavel, I from Russia.
I have problems with the sound system Samson D412. On a quiet sound through both speakers. If you add power, you hear the whistle. On the Russian forums, these speakers do not discuss (maybe not broken). Can anyone help?
Thank you!
Pavel

[Diegongbayo]

Samson Auro D415 Peak Problem.

Thanks for the input. I took Guitician's advice and turned the bias pot down and watched the rails gain 2 or 3 volts. It resulted in about an 80% decrease in heat. I ran it pretty hard for a while and it never broke a sweat. I'm calling the customer and telling him to come get it.

Hi jpglyde,

Can post how did you turned the bias pot down?
If you have a video or photo how to do it?
Pls. Post it.

I'm not a pro-tech. Just know a little.

I have the same problem in my Samson Auro D415.

Thanks

[J M Fahey]

Hi jpglyde,

Can post how did you turned the bias pot down?
If you have a video or photo how to do it?
Pls. Post it.

I'm not a pro-tech. Just know a little.

I have the same problem in my Samson Auro D415.

Thanks

Mmmmmhhhh, this is an old post and jpglyde hasnīt visited here since Christmas.
Iīm somewhat worried about :

If you have a video or photo how to do it?
I'm not a pro-tech. Just know a little.

plus this method is not the proper one:

You could monitor the PS voltages while doing this too, as they will no doubt be going up with reduced loading

which is crude and dangerous.
The proper one is:

You can measure a voltage drop on ballast resistors

jpglyde just got lucky, he might as well have blown his amp into ashes (or rather a black puddle of carbonized plastic).
Please take a couple clean, readable, well illuminated PCB pictures and post them here.
One slightly from left, one slightly from right, because sometimes parts values canīt be seen.
Plus a closeup of the karge grey or whitish rectangular resistrs I see on too-small jpglydeīs picture.
Also post labels stamped on the power transistors seen in the pictures.