Laney CD850S, 2002

2x 200W mixer amp I have the schematics for this amp but anyone familiar with them ?

Problem in protection (falsely triggering occassionally), both amps dropping out. Of course I have not been able to induce activation.

2 separate power amps otherwise apparently the same , both carying output DC protect and overheat protect output relay drive ccts. But only one normally open thermal switch going to one amp only so apparently dropping out that relay only with no apparent interconnect to the other amp. When it was up together I did not think to try shorting the thermal switch but I assume it would drop out both relays and both amp outputs. Anyone know how they interconnect. Also what I assume to be o/p fault DC protect uses 2 470uF back to back electrolytics off the output sense line. I never like to see this form of "non polarised" high C cap , is that just me or anyone else find it iffy, questionable or perfectly valid design-wise. ? More likely a problem with the thermal sw or 12V supply to both protection cct and the fan , rather than a fan problem as it did occur once at sound check and once at switch on. The fan does stop when this happens so unlikely a send/return bypass sw problem, the monitor outputs still continue to work so not a mains failure problem.

There is also a thin low current , signal level earth wire from the ps that has come adrift loose in the case , broken at some pcb solder point presumably, somewhere indeterminate from the schema, anyone happen to know where? Yet again bits of hardware, 2 bolts that hold the heatsink to chassis loose and wandering around inside the case, but probably just incidental to the main problem.

-- 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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You say you found an earth wire off, is it possible that there`s some parasitic hf oscillation going on which is tripping the protection circuits? Does that earth wire look like it was added as an afterthought by any chance?

Ron(UK)

Reply to
Ron(UK)

dropping

output DC

normally

that

switch

line.

just

design-wise.

protection

sound

unlikely

work

that

know

loose

the

Proper jobby, it is on the same connector as one of the main +/-56V +ground connectors but is long enough to go to somewhere on the preamps/ graphics/ effects area of the mixer. Much smaller gauge wire than those power feeds.

I've just emailed Laney on the interconnect and loose wire prob and temp of thermal switch marked Logo - C followed by 2 square wave pulses KSD301 K85 probably (smudged)

Reply to
N Cook

DC

+ground

of

I just checked the switch in a can of water and it goes s/c at 86 degrees C and reverts to normaly open at 71 deg C and no amount of knocking will disrupt it. So the 85 means 85 deg C and perhaps K means Normally Open Bit low for a 2x 200W amp even if fan assisted cooling but as ' no' operation means its immune to false triggering from contact corrosion I will leave that as is.

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

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Reply to
N Cook

Have you checked this amp out with the owner's speakers and cabling?

Reply to
Meat Plow

No wonder I did not get a reply from Laney/Technical Emailing a schematic (not necessary as it was on the www ) is one thing but implied technical criticism is another. The single thermal switch, as i suspected now it is back together, only cuts out the upper (left) channel, I will add a slightly higher th sw to the empty socket of the other channel. Just a signal diode connecting the existing thermal sw to the same pin on the other amp , empty socket, would have coupled both together but I will add a higher temp switch instead to allow half-c*ck continued but still protected use on one amp should the other fail. The rest of the protection is to protect from DC at the output, functional in both amps. schematic (page 8 of 8) on useful Polish site

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The stray low current wire would seem to bridge back one side of the ps to the other , on the same board, when they are both connected to main reservvoir cap common via large traces anyway - there was a lone socket pin in the housing with matching frayed wire taking power to one amp , the other end was with the power connector for the other amp. I've also replaced the 12V fan as worn and wobbly and more to the point, fully cut the casing open at the fan vent area and covered with a wire grill. There was just 14 small slots with a combined area of only 1.5 sq inches, let alone vortexing, so overloading the 3 inch diameter fan and losing cooling efficiency.

-- 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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