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

[Meat Plow]

On Tue, 21 Jul 2009 20:30:28 +0200, Reinhard Zwirner
<reinhard_zwirner@web.de>wrote:

N_Cook schrieb:

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.

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.

 

[Reinhard Zwirner]

Meat Plow schrieb:

On Tue, 21 Jul 2009 20:30:28 +0200, Reinhard Zwirner
reinhard_zwirner@web.de>wrote:
....
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.

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]

N_Cook schrieb:

....
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]

Reinhard Zwirner <reinhard_zwirner@web.de> wrote in message
news:4A674A27.5D9BE50B@t-online.de...

N_Cook schrieb:

...
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

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.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Ron]

N_Cook wrote:

Reinhard Zwirner <reinhard_zwirner@web.de> wrote in message
news:4A674A27.5D9BE50B@t-online.de...
N_Cook schrieb:
...
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

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.

Experience shows that those amps rarely if ever fail through
overheating, so either, the device does it`s job, isn't really
necessary, or isn't carrying out the function you suspect.

In all the cases of destroyed output devices I`ve come across, the fault
has been almost certainly shorted speaker cables - I dont recall a sub
amp failing. I have replaced sub speakers on a couple of occasions which
would suggest that the amps are tougher than the speakers when
overdriven. IIRC the sub amp is a pair of identical amps running in
bridged mode, yes?

The other 'common' faults (IME) are failed mains transformers, smoothing
capacitors breaking loose and broken volume controls

There`s a mod btw for the output transistors, which involves a different
output pair and the addition of a couple of 1N7004 - I have the details
somewhere if you need them.

Ron