[time-nuts] Hp 10544A repair

gianni gianni at islandlabs.eu
Sun Apr 26 15:28:01 EDT 2015

Hi all,
Sorry for bad english
The transistor Q4 has the emitter and the collector reversed; R12 is connected to the collector and the waveform is square wave with duty cycle that depends on the oven temperature; supply voltage = cold, minimun duty cycle = warm.
It is relatively easy to extract the boards and access the oven controller and amplifier AGC.
Pay attention to the black wires (NTC) and red (oven heather).
Remember that the output impedance is about 1000 ohm as for data sheet and check the power supply.
Semiconductor type
Q4 = MJE700
Q2 = MPS A12
Q3 = 2N2646
U1 = LM201NPN = 2N3906

if you want more detailed information in Italian you can contact me directly.
Best regards
John (Gianni)
Il 26 aprile 2015, Luca Dal Passo <iw2lje at gmail.com> ha scritto:
> Hi all,
> Have anyone some experience about 10544A repair? I've recently fixed a
> 10811A, and it is relatively easy to disassemble, but 10544 has not screws
> and the manual does not deal about servicing. Can i try to open the box by
> removing the white plastic tips without demage something? And then how to
> correctly extract the inner stuff? The malfunction is that the oven monitor
> signal is bad and the 10MHz signal has low amplitude and very bad shape
> (distorted), but the output frequency is ok and oven heather and
> control seems to be ok too (current drain from power supply is ok). So
> there are probably some defective components in the output buffer zone of
> the circuit. Another question is that the schematic (thanks to KO4BB!)
> seems to have a mistake about drawing of the oven monitor signal (the pin
> 11 wire is taken between the thermal fuse and the power darlington: how
> does can it work in that way?).
> Thanks and regards
> Luca
> iw2lje
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