Fan problem

--> 12V 0.2A

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

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

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

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

m.

t "

ce

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 tri p it. When it sees 5% of that, it trips. When the fan is running, clearly t he protection circuit is OK with what must be a much lower operating (spinn ing) 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 resistan ce is to be able to separate the ones that might work from the ones that wi ll, clearly, not work without having to test-by-substitution, a not very ef ficient method.

Peter Wieck Melrose Park, PA

** 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.

.... 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.