Regular 2 wire 12V , 0.14A brushless fan. At some point in its history
something has been rubbing against the interior part of the impellor.
Not these days, perhaps dislodged and blown out through the grill.
Black plastic impellor with whitish cicular streaks, the body of the
impellor is black throughout , so distressed plastic going white, like
flexing a bit of black plastic and goes white at the stressing, not
white paint or such.
Anyway that or just normal aging/grime etc it now makes a nasty bearing
noise when warm , so I replaced it.
This is a Mark Bass amp with low speed start and on-demand speeding up
circuit. I replaced it with 12V 2A and that was sufficient to
(presumably) overload the 18V, or so, line off the SMPS and amp goes
into protect. Not even a slight kick of the impellor
Tried the original again, and that is fine.
Tried a 12V ,.15A one and again protect mode, same sort of start up
current draw as the original, but goes into protect.
Tried a 12V ,0.08A half size one and that is ok.
A resistor in the fan control circuit should be 150R and is now 176R ,
so something obviously wrong there, something also wrong in the ps as
well, if it can drop out just from increase of load by 0.01 amp ,
something is awry surely. Something special/odd about Chinese XinFans ?
The fan drive starts in slow speed mode, no confirmation full speed for
2 seconds at startup, which I like to see on such amps , but I don't
think is built-in to these amps

On 08/11/2016 12:21, N_Cook wrote:
12V 2A

-- 12V 0.2A

On Tuesday, November 8, 2016 at 7:21:17 AM UTC-5, N_Cook wrote:

Much Snippage

Questions:

a) What is the actual resistance in ohms of the OEM fan and the replacement fan if measured across the contacts.
b) Have you changed the bad resistor yet? If not why not?
c) Same question of measured resistance on the lower current fan that does not trip into protection mode?

Suggestions:

a) Replace all the out-of-spec resistors with correct replacements. Think long and hard before upping the wattage if there is any chance that the resistor may also act as a fuse under extreme conditions.
b) Perhaps a small thermistor on the fan line might reduce the overload trip - meaning that what the fan pulls running may be much less than what it takes to start it.

On 08/11/2016 13:29, wrote:
On Tuesday, November 8, 2016 at 7:21:17 AM UTC-5, N_Cook wrote:

Much Snippage

Questions:

a) What is the actual resistance in ohms of the OEM fan and the replacement fan if measured across the contacts.
b) Have you changed the bad resistor yet? If not why not?
c) Same question of measured resistance on the lower current fan that does not trip into protection mode?

Suggestions:

a) Replace all the out-of-spec resistors with correct replacements. Think long and hard before upping the wattage if there is any chance that the resistor may also act as a fuse under extreme conditions.
b) Perhaps a small thermistor on the fan line might reduce the overload trip - meaning that what the fan pulls running may be much less than what it takes to start it.


Interesting but I don't know what it tells me, a VDR or some thyristor
cct, start-up hold-off, in the working ones?
Working .08 and OEM .14A ones higher than 10M DVM-R
0.15A 19.3K , DVM-R
and .2A 19.9K

I'll recheck but i think the fan comes on when the relay clicks over, so
not as though the fan is kept out of circuit when the SMPS first starts
up. Even then a pretty light load, even in the sense of start-up
current, or could that current be an amp or more for a mS or so

On Tuesday, November 8, 2016 at 9:19:47 AM UTC-5, N_Cook wrote:

Interesting but I don't know what it tells me, a VDR or some thyristor
cct, start-up hold-off, in the working ones?
Working .08 and OEM .14A ones higher than 10M DVM-R
0.15A 19.3K , DVM-R
and .2A 19.9K

I'll recheck but i think the fan comes on when the relay clicks over, so
not as though the fan is kept out of circuit when the SMPS first starts
up. Even then a pretty light load, even in the sense of start-up
current, or could that current be an amp or more for a mS or so

Sheesh, Guy!!

10Meg vs. 20K +/- and you are not sure what it is telling you?

The system is seeing the non-working fans as, relatively, a dead short. No wonder it goes into instant 'protect mode'.

You need a replacement fan with a internal resistance in the 8 - 12 meg range.

Peter Wieck
Melrose Park, PA

wrote:

On Tuesday, November 8, 2016 at 7:21:17 AM UTC-5, N_Cook wrote:

Much Snippage

Questions:

a) What is the actual resistance in ohms of the OEM fan and the
replacement fan if measured across the contacts.

Meaningless. These fans have a commutation circuit and some FETs in them,
so you will not read anything that resembles a resistance on them.

Jon

On Tuesday, November 8, 2016 at 3:42:12 PM UTC-5, Jon Elson wrote:
wrote:

On Tuesday, November 8, 2016 at 7:21:17 AM UTC-5, N_Cook wrote:

Much Snippage

Questions:

a) What is the actual resistance in ohms of the OEM fan and the
replacement fan if measured across the contacts.

Meaningless. These fans have a commutation circuit and some FETs in them,
so you will not read anything that resembles a resistance on them.

Jon

No. The two that work ohm out at ~10 meg. The two that do not ohm out at ~20K. So, yes, you are seeing 'resistance' on them. Clearly "these fans" are not created equal.

Peter Wieck
Melrose Park, PA

On 08/11/2016 12:21, N_Cook wrote:
Regular 2 wire 12V , 0.14A brushless fan. At some point in its history
something has been rubbing against the interior part of the impellor.
Not these days, perhaps dislodged and blown out through the grill.
Black plastic impellor with whitish cicular streaks, the body of the
impellor is black throughout , so distressed plastic going white, like
flexing a bit of black plastic and goes white at the stressing, not
white paint or such.
Anyway that or just normal aging/grime etc it now makes a nasty bearing
noise when warm , so I replaced it.
This is a Mark Bass amp with low speed start and on-demand speeding up
circuit. I replaced it with 12V 2A and that was sufficient to
(presumably) overload the 18V, or so, line off the SMPS and amp goes
into protect. Not even a slight kick of the impellor
Tried the original again, and that is fine.
Tried a 12V ,.15A one and again protect mode, same sort of start up
current draw as the original, but goes into protect.
Tried a 12V ,0.08A half size one and that is ok.
A resistor in the fan control circuit should be 150R and is now 176R ,
so something obviously wrong there, something also wrong in the ps as
well, if it can drop out just from increase of load by 0.01 amp ,
something is awry surely. Something special/odd about Chinese XinFans ?
The fan drive starts in slow speed mode, no confirmation full speed for
2 seconds at startup, which I like to see on such amps , but I don't
think is built-in to these amps

Curiouser and curioser. I found a pretty knackered , high impedance, 12V
0.16A fan and that worked fine.
Removed fan and placed a pot across and dropped down to 10K ,
eventuallly, and no protect mode. Tried fixed 8K2 and no protect mode.
Put an impedance "break" as far as DVM-R is concerned, of a Darlington
BDX47 and 10K bias R, so DVM-R across the new low impedance fan I was
hoping to place in there now measuring 2M . Dropping 0.9V on bench ps.
But still triggered protect mode of SMPS.
So not simply resistance problem.
SMPS is perfectly happy with 78 &79 V regs off those SMPS Tx taps, but
the fan supply is taken off before a choke, significant?

I was mistaken , fan supply is downstream of the choke, same point as
input to a 7812. I tried a ferrite ring choke in the 10K resistance fan
line, but same protect mode scenario

wrote:

On Tuesday, November 8, 2016 at 3:42:12 PM UTC-5, Jon Elson wrote:
wrote:

On Tuesday, November 8, 2016 at 7:21:17 AM UTC-5, N_Cook wrote:

Much Snippage

Questions:

a) What is the actual resistance in ohms of the OEM fan and the
replacement fan if measured across the contacts.

Meaningless. These fans have a commutation circuit and some FETs in
them, so you will not read anything that resembles a resistance on them.

Jon

No. The two that work ohm out at ~10 meg. The two that do not ohm out at
~20K. So, yes, you are seeing 'resistance' on them. Clearly "these fans"
are not created equal.
But, clearly, if it was TRULY a 10 Meg resistor, the fans would not produce
any airflow. When you get enough voltage on them, the circuitry turns on
and starts drawing current to spin the rotor.

The 20K ones might have a popped component, or just a different control
circuit.

Jon

On Wednesday, November 9, 2016 at 2:46:10 PM UTC-5, Jon Elson wrote:
wrote:

On Tuesday, November 8, 2016 at 3:42:12 PM UTC-5, Jon Elson wrote:
wrote:

On Tuesday, November 8, 2016 at 7:21:17 AM UTC-5, N_Cook wrote:

Much Snippage

Questions:

a) What is the actual resistance in ohms of the OEM fan and the
replacement fan if measured across the contacts.

Meaningless. These fans have a commutation circuit and some FETs in
them, so you will not read anything that resembles a resistance on them.

Jon

No. The two that work ohm out at ~10 meg. The two that do not ohm out at
~20K. So, yes, you are seeing 'resistance' on them. Clearly "these fans"
are not created equal.
But, clearly, if it was TRULY a 10 Meg resistor, the fans would not produce
any airflow. When you get enough voltage on them, the circuitry turns on
and starts drawing current to spin the rotor.

The 20K ones might have a popped component, or just a different control
circuit.

Jon

You miss the point - no surprise there - what the "protection mode" sees is the initial state of the fan, which is around ~10 megs. Which does not trip it. When it sees 5% of that, it trips. When the fan is running, clearly the protection circuit is OK with what must be a much lower operating (spinning) impedance.

Yes, perhaps a different circuit, no sh*t. Point being, yet again, is that the fans are not created equal. And the point of measuring initial resistance is to be able to separate the ones that might work from the ones that will, clearly, not work without having to test-by-substitution, a not very efficient method.

Peter Wieck
Melrose Park, PA

Nutcase Kook wrote:



This is a Mark Bass amp with low speed start and on-demand speeding up
circuit. I replaced it with 12V 2A and that was sufficient to
(presumably) overload the 18V, or so, line off the SMPS and amp goes
into protect. Not even a slight kick of the impellor
Tried the original again, and that is fine.
Tried a 12V ,.15A one and again protect mode, same sort of start up
current draw as the original, but goes into protect.


** The above drivel makes no sense whatever.

The switching PSU in the Mark Bass "Parsec" series is unregulated and has no remote shutdown system. The DC supply for the fan is also unregulated and not sensed.

"Protect" mode, when triggered, mutes ( labelled DIS on the schem) the input signal the power amp and detects overtemp or excess current in the output MOSFETS.

The speaker relay operates independently and senses only large DC offsets.

http://bmamps.com/Schematics/Mark_Ba...le_Mark_II.pdf



..... Phil

Enough of this flaffing around, should have been just a change of fan
job. Found a "high impedance" 12V ,0.16A fan in a parts mule and that
works fine, incidently from a linear ps amp.
I'll assume its something to do with the 0.1sec or so full tilt, fan
start up function of the control circuit. Instead of initial 2 seconds
or so to audibly confirm to the owner that the fan is working, just a
short kick start before dropping into low temp speed . But potentially
18V over 12V fan for 0.1sec and perhaps some added monitoring variant
somewhere in the SMPS , in this 2013, Mini CMD 121 flavour of mark Bass
, different to the only representative Mark Bass schematic that is out
there.
Anyway no nasty ticking of the SMPS going into protect at switch on and
normal running fan noise and increase speed on warming up.
At least anyone else coming across this problem has now some clues as to
what is going on.
Incidently the usual scratched off ident to the SMPS supervisor chip,
dicussed and collectively identified previously on this board.