I am working on an HP EPM 441A which seems to be in good shape except that it doesn't want to turn off. Pulling the plug out and then plugging it back in right away just turns it back on again. The switch acts like it is dead, except I know it is not: If I hold it down while plugging in the ac power, the unit will enter "stand by" mode as it should, and then the power switch turns it on when pressed. The switch is described in the Service Manual (it is a "soft" switch which turns the 3 power supplies on or off). Also,. if left unplugged for a longer period of time (like overnight) the switch works normally the next time...but only once! The problem comes right back the next time I use the switch. I thought it might be a backup battery problem, but the battery reads 3.1 volts, which I think is OK. The service manual has no schematics, and I am hoping that someone on this forum is knowledgeable about how this circuitry was designed and how it can be troubleshot. For example, there is the word "reset" screened on the Processor Board near the battery, but the manual does not mention it and I can't tell exactly which circuit pads are associated with the reset function!

Hope someone can help! Thanks

Vic

From: "Richard Knoppow" <dickburk@...>
To: [email protected]
Sent: Monday, July 29, 2019 1:55:18 PM
Subject: Re: [HP-Agilent-Keysight-equipment] Testing a 2-01C Diode

Try testing the probe with a solid state diode, nearly any
diode will do. Hook it up across the terminals for the tube with
correct polarity. See if it works. If it does the tube is
probably bad, if not the problem is something other than the
tube. Check your tube testing set up the same way. The 410B is a
very simple meter, essentially a DC meter with a series diode
rectifier for AC measurements.
You could also test the meter by putting a low DC voltage
across the diode output terminals.
Maybe your worn out 9V battery drops to zero with any sort
of load, I've found some like that. Try a plain old D cell.

On 7/29/2019 9:18 AM, n4buq wrote:

I tried setting up a test for the diode using approximately a 3VDC source
(a very weak 9V battery I happened to have on hand) with a 3.3K resistor
in series between the anode and cathode (naturally, with the heater
connected and sufficiently warmed up). I could not measure any voltage
across the resister regardless of the polarity of the source voltage. I
also tried it with the DVM in series with the resistor/voltage source and
still could not detect anything even close to 1ma.

Thinking that was more-or-less conclusive of a bad tube, I tried this with
a NIB EA53 (adjusting the heater voltage accordingly) and still could not
see any significant current flow regardless of the polarity of the source
voltage.

Unless _both_ tubes are bad (unlikely but I can test the EA53 in the
working probe to verify that one), then I think this test setup is somehow
invalid (although I don't see how with such a simple setup).

I'm not where I can get to my workshop for a while so can't report more
findings until I get back there but thought I'd pass this along.

Thanks,
Barry - N4BUQ

--
Richard Knoppow
dickburk@...
WB6KBL

I tried setting up a test for the diode using approximately a 3VDC source (a very weak 9V battery I happened to have on hand) with a 3.3K resistor in series between the anode and cathode (naturally, with the heater connected and sufficiently warmed up). I could not measure any voltage across the resister regardless of the polarity of the source voltage. I also tried it with the DVM in series with the resistor/voltage source and still could not detect anything even close to 1ma.
Thinking that was more-or-less conclusive of a bad tube, I tried this with a NIB EA53 (adjusting the heater voltage accordingly) and still could not see any significant current flow regardless of the polarity of the source voltage.
Unless _both_ tubes are bad (unlikely but I can test the EA53 in the working probe to verify that one), then I think this test setup is somehow invalid (although I don't see how with such a simple setup).
I'm not where I can get to my workshop for a while so can't report more findings until I get back there but thought I'd pass this along.
Thanks,
Barry - N4BUQ

From: "Barry" <n4buq@...>
To: [email protected]
Sent: Saturday, July 27, 2019 8:15:28 PM
Subject: Re: [HP-Agilent-Keysight-equipment] Testing a 2-01C Diode

I plan to test it per the suggestions. It is possible, though, that I might
have damaged it feeding the 50-ohm terminated output of the 3310B directly
to the tube tip as I expect that would have produced more than 1mA unbridled
current from the generator. I did that before I read about the 1mA rating.

This poor probe, though, had multiple problems so the tube might have been
bad when I got it. I mentioned that the spring connector was falling out of
its slotted socket, but I also discovered that the cable's braid was not
connected to the sleeve of the plug so the heater couldn't work. I can't
tell if it was that way from the factory or whether someone did that
intentionally (and I can't figure why anyone would want to do that).
Connecting that let the heater start working but have not successfully
gotten a signal through the tube.

If the tube still checks bad, then I'll be looking for a replacement tube.

Thanks again,
Barry - N4BUQ

----- Original Message -----

From: "Chuck Harris" <cfharris@...>
To: [email protected]
Sent: Saturday, July 27, 2019 5:34:44 PM
Subject: Re: [HP-Agilent-Keysight-equipment] Testing a 2-01C Diode

Well, it is a detector, not a rectifier. A very special
detector in that it works from about a milivolt through
a kilovolt.

-Chuck Harris

n4buq wrote:

That's the way I thought of it. It's just a diode and should act like
one
if it's good. What gets me is the relatively tiny forward DC current
rating. For tube construction, that just seems odd - especially
considering it's rated at 1000V.

Thanks,
Barry - N4BUQ

Consumer gear is rarely cleaned properly after soldering. Flux residue is hygroscopic. It absorbs moisture from the air and with the shift to ever lower voltage levels for logic, the noise margins are very narrow.

My CD player got to where it would play pressed CDs, but not CD-Rs. Then it would not play either. I opened it, up and found a small bit of flux near an MCU. I cleaned it with isopropyl and it has worked fine since. Though it did require a 2nd pass after several months. But it's been fine now for several years. I'm getting close to a dozen "repairs" which were nothing more than cleaning the board. The first was a VCR/DVD remote.

The most spectacular such "repair" was an ebay 34401A which arrived heavily used and giving completely wonky readings. When I opened it up there was 1 cm spot of flux residue around an LF357 which had been replaced. I cleaned it and it not only works flawlessly, it is the more accurate of my 34401A as demonstrated by 48 hours of measurements using an LTZ1000 voltage reference from the EEVblog USA Cal Club. It reads 3-4 ppm low on the 10 V scale and varies 1-2 ppm from 69-85 F. Measurement noise is +- 0.5 ppm.

I have plans to build a small isopropyl pressure washer out of an electric fuel injection pump and and spray gun with a distillation unit to recycle the alcohol. On a lot of consumer gear it is very difficult to get to the boards without several hours of disassembly and reassembly. To avoid that I want to be able to stick a spray wand in where I can't otherwise reach and just hose it all down.

Not even any offers…? not many builders/experimenters remaining out there I guess.?

>
>
> Still have the following available… all tested and working properly.? Pics on request.
>
>
>? ? ?4284a? lcr(z) $1650. Into storage trailer this week
>
>? ? ?4285a? lcr(z) $1650. Into storage trailer this week
>
>? ? ?83712b. 20GHz sig. gen, $1800… offers??
>
>? ? ?sold
>
>
>? ? ?sold
>
>? ? ?8720d 20GHz VNA. $6150… offers ?
>
>? ? ?8562a 22GHz spec an, $1250… into trailer this week
>
>? ? ?All tested and working fine. Once into trailer… next of kins' problem

>
>? ? ?Thanks for looking,
>? ? ?Pete wa2odo?

Accepting fair offers…?