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Speaker protector on Soundlab SP 800 amp, 2002

Anyone familiar with this amp? worked for years with the present owner but there is a quantity of circuit , each channel , that has been removed. A "friend" decided to short a speaker line to give the current fault , but I'm faced with a lot of post-production modification that does not look made by the manufacturer. Cropped tr legs and desoldered Rs,Cs, 4Tr,7R,2C all x2. Removed at manufacture or previous owner? Leaving this circuit in place with 2 Triac/scr. Unknown TO92 size SCR (on overlay) marked (unclear on each channel examples)

08D 09 2 lines from the disconnected circuitry went to the left and rightmost pins of that SCR. Nothing at any time to the centre pin. C is actually 2 back to back 220uF, 50V for pseudo unpolarised C. May need to go into message source for equal space font for the following

o-------------------------------|---o Speaker | .-. | | | | | | 10K |BTB24-600 '-' ' | _|_/o-------------o o o V_A SCR | | | | | | | | | | --- | --- 110uF,100V | | o------'-------------------------------o Ground

Can anyone identify the SCR ? Given a nominal one there, in the correct orientation , can the scr act as a diac? or maybe erroneous overlay marking. Can whole cct act as a crowbar speaker protector in event of amp failure to DC output.?

Reply to
N_Cook
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Looks like a DC crowbar circuit. Don't immediately recognise that particular device, but general convention for type numbers on SCRs and triacs, would suggest maybe a 24 amp 600v rating ?

Arfa

Reply to
Arfa Daily

I've seen that in some of the higher end older high power Marantz amps if memory serves. It's a crowbar to shunt DC from a shorted final. The BTB24 is a Triac. Use a 25 amp 800 volt for replacement.

Reply to
Meat Plow

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Not the TO220 one, I have full data on those The problem is the TO92 little one marked

08D 09 that I cannot identify as small SCR or diac in a 3 pin package, represented as 3 dots, marked SCR in the ASCII
Reply to
N_Cook

looks as though someone else has been here with a different amp

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.. The schematic calls this burnt component a "triac driver sbs bv thresh" and on its twin (in the non shorted channel) its only labeled "08d 25". This is in the protection circuit of the amplifier which unloads the outputs if there is a problem.

... This is a 3 leaded device btw

so the 09 in my case and 25 for him is probably datecode

googling about ,perhaps a DIAC08D, would that be an 8V diac ? sounds about right value of bilateral switch for a 400 W amp into 4R

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

From that previous thread and mention of MBS4993 I downloaded that datasheet and it looks as though a sort of Darlington triac arrangement in the soundlab amp

Reply to
N_Cook

I'm

by

I normally charge an engineering fee for equipment that isn't supported and not obvious. I won't spend more time on it than the customer can pay. Engineering projects and prototypes require investors.

Reply to
JB

The amp channel failed to s/c , knocking out fuse, so speaker protector did not come into play.

The way to confirm the identity of this "08D" device is to remove one and check for a switch action , at about 8V, on a current linited bench ps.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

Oh ok. Maybe look up some triac model circuits and see if you can find something similar. Either Fairchild or Motorola should have some errata you could use.

Reply to
Meat Plow

So it's an SBS Diode Thyristor. Looks like you've identified it.

Reply to
Meat Plow

Another oddity with this amp. Each channel has one floating, nominal zero DC, connected to true ground by a 50 ohm NTC thermistor, why thermistor ?.

The missing circuitry may relate to fan proportional control of 1 or 2 fans going by overlays. Only one , on constantly, in this version. But why the 2 DC lines back from the output on each channel. This is an all N-channel mosfet amp. Can they have a DC offset if driven hard?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

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