HK Audio / LUCAS (Germany) ,2001 2x 150W power amp

Nothing wrong with these 2 mystery 2 pin items, but I like to identify such mysteries and place on the www.

In the fan air-stream a 1.5mm sphere I assumed to be a bead thermistor , measures 58 ohm, in circuit, but no change with freezer spray. Blue bead with a white letter H marked on it.

2 off per channel amp, black epoxy potted lumps, about 8mm cube, with a large letter M on them. Measure about 150 ohm , in circuit, and no change on freezer spray

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

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N_Cook
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overlay for the sphere says TR3, T for transistors overlay for one of the black lumps says IC2

Reply to
N_Cook

T - hermal R - esistor maybe ? Try heating it rather than freezing ?

Arfa

Reply to
Arfa Daily

With the bead one, thats what I did first, but only held between fingertips, usually shows change and + or - . I will retry with a nearby soldering iron on Monday. My thinking was tiny bead thermistor would be far more responsive than disc or rod but maybe very insensitive, any chance a humidity or velocity sensor somehow ie in use it is heated? , will have to try powered up

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

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Reply to
N_Cook

Ah, yes. That's a distinct possibility. I had a problem with the MAF in my car some time back, and I kept the one that the garage took off, just to have a look. It had a tiny bead device in the airflow path, which I understand is heated by a fixed voltage, and then cooled by the airflow. The degree of cooling alters the current flow through the device, allowing, once ambient temperature of the intake air has been factored in, the mass of air being drawn by the engine at any instant, to be calculated, to achieve the correct fuel mixture. Maybe your device is similar and is there to ensure that the fan is shifting the required amount of air to keep the temperature of the output at below the design maximum ??

Arfa

Reply to
Arfa Daily

The

once

air

temperature

I'll blow on it on Monday

They other mystery , 2 pin IC ? Is there such a thing ? I suppose overlay graphics packages come with a pallette of letter designations and if one does not fit then they re-use another.

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

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Reply to
N_Cook

Black cubes are in fact 4 lead, 2 from the top and down the side and 2 underneath. One pin to 0V and the other to -preamp rail voltage, beyond that will be Monday

Reply to
N_Cook

It is a L.U.C.A.S 600 with 300W and 2 x 150W outliers My guess , from the way the leads are at either end , that the black cubes are LED/LDR couplers

Reply to
N_Cook

cubes

Thanks but non diagnostic repair this time. The vol knobs are not recessed and very exposed , underneath, for bad handling over the tailgate of a van, so stove-in, needing the pots replacing.

The black lumps must be LED/LDR couplers. I've not tried this test before, amp unpowered.

2 DVMs, 3V over probes in "diode test" over the long pins and 150 ohm drops to 142 ohm measured on another DVM, over the other pair of pins. Change from diode to 200 ohm scale and the resistance changes to 146 ohm. Reverse the active probes and stays at 150 ohm. Will see how that speed sensor works , tomorrow.

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

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Reply to
N_Cook

cubes

On powering there is only 7mV over this small blue blob that measures 58 ohm but looks like a tiny ceramic cap in the fan stream. Could you send me a copy of the schematic , if not bigger than 4 Meg to fastmail.fm @ diverse8 (swapped around either side of the @ )

if it is a protection cct it would not activate if the fan stops

Reply to
N_Cook

It`s in my Dropbox

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Cheers

Ron

Reply to
Ron

Cheers old boy. Appreciated.

Arfa

Reply to
Arfa Daily

ohm

diverse8

Thanks. all received The fan blows out so this track-side mounted component is not so obviously in the airstream now, but no reason why it could not be mounted component side other than maybe too near a pair of W/W droppers. TR3 is the preset not this blob, which is unlabeled on the board and overlay views, but seems to be the PTC thermistor ? on the first image in that pdf, labelled R84 setting the FET DC for the amp input. Can thermistors go wrong ? Placing a 700 degree F soldering iron tip 5 mm or so under this bead changes the resistance from 58 to 66 ohm, ie swamped by the 2K2 resistor so totally ineffective. So is PTC B59 80C some sort of miniature 80 degree C Woods metal thermal fuse, if so why is it not near a heatsink, or is monitoring general air temperature good enough? If the fan stops then this sensor is nowhere near any heatsink and would be monitoring fresh air being consequently convected in through the fan port which is just plain daft.

Reply to
N_Cook

Is there a name for a more non-linear thermistor with much lower coefficient than usual in the below x2 "set temperature" range and sharper knee/inflection than usual.? I think I'd like to see a thermal switch on a heatsink as well.

Reply to
N_Cook

Fan bearing would be grumbling at 80 degree C. Can anyone identify the component graphic on the pdf of that thermistor ? variable resistor, 2 arrows and a squiggle. I returned to freezer spray on that blob, with a 1mm bore tube this time added to the spray can. NTC , going up to 100 ohm . And in case it was due to the spray movement I wrapped the blob in cotton wool , confirmed NTC below room temperature, so a very odd characteristic.

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

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Reply to
N_Cook

N_Cook schrieb:

Could it be that it's a fan with integrated temperature control?

The fan gets its power directly from one of the two 32 V ac windings via R3 (page 6), R85 and D15 (page 3). I'm not able to find any fan control circuit in one of the schematics.

HTH

Reinhard

Reply to
Reinhard Zwirner

?

I would not say integrated but intended to be associated with, monitoring the airflow pulled by the fan. Combined with the LDR part of the LT3011 LED/LDR in the FET control of the amp, . Unfortunately being mounted right over the fan (pulling air out) it would have the opposite control effect if the fan stopped, whether due to 80 degree C air or any other reason.

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

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N_Cook

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