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The capacitors are fine... I did change the ones on the PSU board, but left the large cans be.

However, there was an open diode in the bridge rectifier circuit which was the cause of the ripple on the 10V rail

I also made a mistake and do have all the colors, it was a setting on the monitor.

Now there is still ripple on the 3.6V line which appears to be caused by the 3.6V regulation going into current limiting. It looks like something on the A3 field timing board, though nothing appars to get hot. The A3 board is quite complex....

/g/TekScopes/photo/296482/3889932

Hi all,

So last year my venerable old 2465A developed a weird intermittent fault. After some time - arbitrary and not temperature related - this fault would arise whereby the screen would become *really* bright with some spurious artifacts showing up as well. When this happens, the screen brightness control fails to have any effect and I cannot turn that dazzling brightness down.
Now, from what I've read, I need to monitor TP73's voltage ('grid no. 1' to the CRT) and see if it changes when the fault arises. So I've stripped the casing away and removed the HV safety/warning shield from the HV supply board A9 and attached a scope probe to TP73. The service manual provides a diagram of how the waveform on TP73 should look so I'm all revved-up waiting for the fault to materialize (which it invariably does when I try to use it to check anything). Guess what? I've had the damn thing on now for 5 hours and it's not missed a beat! Behaving perfectly normally with no sign of any screen issue at all. Bloody intermediate faults. I hate 'em!!

Jinxie

Hi Friends,
as planned, I went today to Andrea and checked his beautiful 11302A, using the same VOM and HV probe. Well: all its values are exactly like mine. Only the ripple seems to be a little lower.
So, as you suggested, the problem was only in the HV measurement, either because the ripple, or for a HV probe error.
Since when I adjusted the voltage at U1540 pin 4 to 1.600 V, the problem did not manifest itself again. So now I remain waiting...
Thanks anyway for your suggestions, now I proceed with other adjustments and maybe I ask again your aid.
Gianni

Hi all

I have dialed in the voltages, which brought back most of the logic that generates the patterns, but there is still something wrong with the heater circuit.

It generates a picture now, though it's missing two colours and has artifacts in it: /g/TekScopes/photo/296482/3889912

Unfortunately Mark is right, the unit needs recapping because ripple is all over the place and out of spec on all rails (10 V rail has 2V of ripple - yikes)

You may do better in the [HP-Agilent-Keysight-equipment] group

Hello John,
wow - thank you for the quick reply!
I'll try it out later and report back!
It's really strange that there isn't much information about this online...

Best regards,
Eric

Hi Martin,

Thank you for your tip. OMG – I thought I just shared the picture of the probe.
Just deleted the link - it shoudnt work any more.

Best regards,
Eric

Hi.

I have a HP54502A in fairly good condition I want to fix for my workbench. It fails on A/D test (pass D/A and rest) on CHANNEL 2 only. I have no schematics, just the SM, and if anyone knows of link to any it would be appreciated.

Anyway, have anyone else successfully fixed this error before and what was it? I did see a blog online with at short in PS but ALL voltages seems OK and 5.2 adjusted according to SM. I have swapped the 2 ICs with heatsink around just to eliminate that. In lack of a schematics does anyone knows which IC is the DAC (A/D converter) so I at least can have a look around it and compare channels (CH 1 works perfect).

Any hints are welcomed.........

PS. the Dallas chips has been replaced before I got the scope with a DS1230Y so guess that is not the reason?

I got the schematics for a 54601a is that too far off or similar in chip sets used?

Cheers

Hi Mark,

Thanks for your advice. I tried reseating the ribbon cables and the text came back, but was now wobbling. The only adjustments I remember significantly changing were C114/C124 (CH1/2 input capacitance), because I mistook it for the compensation.

However, I tried turning on the x10 magnifier and it started shaking much more violently, but then resistor A10R801 (part of the Horizontal Output Amplifier) blew up/melted. The unit can power on briefly, and I can see the resistor glow for a moment before it shuts itself off. If it's worth anything, Q801 (the transistor connected to it) got so hot that it burned my thumb, but that was before I turned on the x10 magnification.

Is it likely that this resistor was just on its way out, or will it fail again when I replace it? And if it's the latter, how do I go about figuring out the problem, especially since I can't get the unit to stay on to test voltages, etc.?

The 2246 service manual can be found at . The schematic with R801 is on page 253.

Thanks again for the help.
Aneesh

Perhaps not very helpful on the topic but nevertheless: you should avoid putting all your private pics on the web!

It might even be dangerous for us as there is no guarantee the files do not contain any harmful content.

Better use the space forseen in this forum, I guess.

cheers
Martin

It's not really clear which LED's are lit as lots of them light up, before all switching off.

Wondering which tests can be done by a process of elimination in order to rule out the faults?

Considering that the LV test points all appear to be good, testing the HV section might not be a bad idea, 'if' my testers can handle it?
Checking the A5 board waveforms and voltages must surely be worth a go too...

My main issue is time. Hence my writing here instead of reading every page of the 323 page Service Manual several times

Eric,
From some notes I took long ago.
Pinout: (I don't know actual numbering scheme)
A B
C D
E F
G H

A--Signal
B--Shield
C--Violet, +5V
D--Black, -5V
E--Brown, +1.53V when DC Reject ON, 0V when off
F--Red
G--White
H--Blue, pulses to +2v for 1x, pulses to -2v for 10x

White and/or Red might have something to do with bandwidth limit control
Orange wire: No connect?

--John Gord

On Fri, Feb 21, 2025 at 3:40?PM James55 via groups.io <james_55=
[email protected]> wrote:

Wow. That A/B Button trick is one worth remembering!...

Sure, but which FP LED is lit before you exit the diagnostic monitor?
This tells you which POST is failing, which may help pick a direction for
diagnosis.

Aneesh,

I suspect you pulled a connector or more loose by removing the case. Check and reseat connectors. This can easily happen removing the case and/or doing any checking without you noticing. A couple of mm movement will disconnect. Dirty switch contacts will cause problems like this.

Having a 2252, the condensers in yours are likely the same in the scope. I did recap mine with NIchicon, ULD, UHE, UCY and LGR. The power supply board is tedious to remove. I did oil the fan with the supply removed. Bad caps will cause problems. If you have any RIFAs in there, replace them on-sight.

Mark

Hello,

I have a Tek P6248 differential probe, on which the micro wires in the head have unfortunately broken off. Unfortunately, the pinout of the wires, or the "Cinch" plug, is no longer recognizable and I haven't found anything online, even though this seems to be one of the most common problems with the probe.



Perhaps someone here can help me.

Best regards,
Eric

I recently acquired a Tektronix 2246 oscilloscope. It seemed to be working fine until I opened it and tried to check the test and self-calibration voltages (some of which out of the limits, but it is the same before and after the issue happened). Now no text is displayed, and the Readout intensity knob makes a dimmer version of the trace show up above it. If I try and open the Service Menu, etc. the screen just turns blank but I am able to quit out of it by pressing the right button.

Photo in /g/TekScopes/album?id=300837

Any suggestions for how to fix this? This is my first time repairing an oscilloscope, so any pointers would be appreciated.

Thanks for your time.

Eng,

Q944 is a 2N3565 (151-0432-00), 610-2N3565 Mouser part number. The zener can be replaced with a 78-BZX85B6V2 (Mouser part number).

Mark

Looking at 330 ohm axial lead resistors on Mouser, no 10% parts, only 5% or better. Quantity 1, 1 and 5% parts both $0.10.

At my previous employer,? we only used 1%'s everywhere. Any small difference in cost was more than made up by only stocking 1 component instead of 2.

John?? KK6IL

Mmm!?

Ok, so taking a closer look at the A5 board there are at least 4 IC's which have either been removed or 'attempted' to be removed.

Gonna have to pull these over the weekend, check or replace them and install sockets.

I'll be back...

On Fri, Feb 21, 2025 at 01:58 PM, <zheniak@...> wrote:

Indeed
/g/TekScopes/photo/300835/3889065?p=Created%2C%2C%2C20%2C2%2C0%2C0

While you are at it, you should check the resistor in series with the blown RIFA, current limiting NTCs for drift, and the resistors in parallel with the NTCs for damage.

There are three more RIFAs on the other board if it is similar to 2465B/2467B.
Ozan