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

[N_Cook]

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

 

[N_Cook]

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

 

[N_Cook]

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

Arfa

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

 

[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

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.

 

[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

 

[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

 

[N_Cook]

Would you like the circuit diagram?

Ron

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.

 

[N_Cook]

Would you like the circuit diagram?

Ron

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

 

[N_Cook]

It's in my Dropbox

http://files.getdropbox.com/u/1365762/LUCAS Schaltplan.pdf

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.

 

[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.

 

[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.

 

[Reinhard Zwirner]

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.

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

 

[N_Cook]

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

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.

 

[Reinhard Zwirner]

On Tue, 21 Jul 2009 20:30:28 +0200, Reinhard Zwirner


I've never seen an AC powered fan with internal temperature control in
all my years in service and seeing literally hundreds of different
fans. But this by no account means they don't exist.

Of course the the ac voltage is rectified by D15 and, additionally,
filtered by an electrolytic capacitor ...

Sorry for my obviously misleading formulation.

Ciao

Reinhard

 

[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,

IMHO the LT3011 LED/LDR is part of a separate control loop which
limits/reduces the PA's input voltage as a function of the output
signal.

The FETs IMHO are part of a second control loop which limits/reduces
the PA's input voltage as a function of the temperature at PTC R84
(page 1). Maybe that's your "blob" ...

HTH

Reinhard

 

[N_Cook]

IMHO the LT3011 LED/LDR is part of a separate control loop which
limits/reduces the PA's input voltage as a function of the output
signal.

The FETs IMHO are part of a second control loop which limits/reduces
the PA's input voltage as a function of the temperature at PTC R84
(page 1). Maybe that's your "blob" ...

HTH

Reinhard

Agreed that is the intended function of the blob but it should be nearer a
heatsink , rather than the fan. The whole air handling system is in a duct
so it could be anywhere for monitoring internal air temperature , but
directly over the fan is not where it should be. If the fan stops then cool
air would be convected in there, falsely telling the control that the amp is
now cooler, and would accelerate the already hot amp to quick destruction.

 

[obylica]

please help me I want HK lucas with 300W and 2 x 150W outliers schematics!

THX