Re: 1502 TDR project

fiftythreebuick
 

Mark, as Tom said, it can be a transient condition that trips the power supply.

When developing a battery emulator for my units, at one point mine would fail when the unit was first powered up after sitting idle for a long time, but if you just turned the power off and right back on, it would work every time. The inrush current to all the capacitors in the 1502 was causing a transient low-voltage condition that would trip the power supply. I just increased the size of the capacitor in the emulator and she runs first time, every time now.

As he said, gotta pay close attention to the "subtleties" of this one! :-)

Tom

On Mon, Dec 9, 2019 at 08:53 AM, Tom Gardner wrote:


On 09/12/19 16:38, Mark Pilant wrote:
Hi Tom.

I haven't tried supplying power directly to the banana plugs, but the
parallel cap/resistor battery substitute (ala TekWiki) seems to work
fine, as the battery meter on the front panel indicates the battery is
"good" and I do see 14.4VDC supplying the DC converter.
That's insufficient.

You realise that PSU trips if there is a transient overvoltage. At that point
the voltmeter reads "excessively good" :)

I presume you have read the circuit operation section of the manual?


So it would seem the battery portion of the power supply is working and
I need to determine why the rest of the power supply isn't working.

My general sense is the DC converter is an oscillator driving the T6535
primary to then generate all the secondary voltages needed.  I suspect
the oscillator isn't oscillating (well?), but I'm not sure of the best
way to investigate.  (Not sure how many ways there are to shut it down;
lack of a battery is one.)
One way is the overvoltage detection, via q6547/8/9.


I'm a little wary just probing around with my scope (7904 with the usual
vertical / horizontal plugins), because of potential ground issues.
Although I do have a Tek 224 I can use that shouldn't have any ground
issues.
If you power off a bench supply, then clipping the scope shield to the chassis

is fine.

The 1502's transformer is fully isolated, so**clipping the scope shield to the

chassis is fine.


I just checked, and the power supply for the 1503 is the same as the one
for the 1502.  I may be able to open up my 1503 and use its power supply
to troubleshoot the 1502 power supply.
Yes.

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