hp 54503a scope psu

[m3vuv]

Hi all,i have this hp 5450a scope with a dead psu,so far i have found one dead fet(i think its a fet) marked 350 qyq003,google finds nothing on it,,i wondered if i can use a pc atx psu in this?

[m3vuv]

can anyone id this part?,see pic.

[m3vuv]

maybe this will help but looks crap to me as far as service manuals go,totaly piss poor imho

[gamalot]

Why can't it be LM350?

https://pdf1.alldatasheet.com/datasheet-pdf/view/11671/MOTOROLA/LM350.html

[m3vuv]

that is a possibility as my component tester says unknown or damaged component,i find it does that with any voltage regulator !

[m3vuv]

sort of dont know where to go next with this as no schematics etc,do i try and homebrew sommat,dont even know what voltages should be on the ribbon cable output from the psy tho!,can anyone help?,pretty please. tia.

[Wallace Gasiewicz]

This fellow has always had good copies of manuals:
http://artekmanuals.com/
Even when I can get free copies, I sometimes have to order from him because his copies are more clear.
I did not look for this HP unit, but his manuals usually come with clear schematics.

That said, The manual provided here gives you a place to start: Page 91 shows the PS TEST POINTS.
The troubleshooting steps outlined earlier in the document should help.
As a comment, sometimes the PS in HP equipment "shuts down" if there is an "overpower" sensed somewhere in the unit that can occur on another board (not on the PS board itself), if you read the manual, maybe it will tell you about that problem.
Just a shorted cap can and has done just that.

I think that part is a voltage regulator. I do not think I have ever seen an old HP unit with a FET  that big.

Wally

[m3vuv]

all i have managed to find is this,not very clear tho,seems hp dont want these to be repaired!

[m3vuv]

found this but its in french.http://www.radiocollection.be/fr/fr.htm

[Andrewausfa]

Have you actually checked the voltages given on page 91?

[m3vuv]

yes the voltages on the big connecter that goes to the mailboard are as follows,factory recomended voltages first followed by my readings,this is with a 2 ohm load between the +5.2v rail and ground,
pin1+5.2v,mine+2.8v
pin2+5.2v mine+2.85v
pin3+5.2v,mine+2.86v
pin4+5.2v,mine+2.86v
pin5,gnd,mine gnd
pin6,gnd,mine gnd
pin7,gnd,mine gnd
pin8,gnd,mine gnd
pin9,+3.5v,mine +0.4v
pin 10,gnd,mine gnd
pin 11-5.2v,mine +0.6v
pin12,gnd,mine gnd
pin 13+12v,mine +9.1v
pin 14,gnd,mine gnd
pin 15 -12v,mine -2.7v
pin 16,gnd,mine gnd
pin 17+12v,mine,+0.52v
pin 18-5.2v,mine,+12v,mine,+0.58v
pin 19+15.5v,mine +0.65v
pin 20+5v,mine+0.04v
also measured the tip l755a as oscillating at 160hz on the transformer primary.,not sure where to go with this.

[m3vuv]

could an atx pc psu be made to replace this?

[Wallace Gasiewicz]

There is someone on the Groups.io group in the HP equipment group:  https://groups.io/g/HP-Agilent-Keysight-equipment/messages
who as used another PS in an HP 54501. Maybe this is the same PS that you have. He used an ATX.There is some instructions in the file section. Join the group and look in their file section.
Apparently there is no schematic for the PS. It was made by someone other then HP
Here is what I could find:

Just to pass it along. Recently purchesed a HP54501A with dead power supply. They are expensive and hard to find. Here are the cross numbers if interested: HP # 0950-1879, Boschert 700040-01, HP# 0950-2369 (sub), XL131-3604E, or HP1650 series Logic Analyzer uses same.
    I took a different approach, I removed the twenty pin header from the power supply board. I bought an old ATX supply with the minus five volt supply ( It has a white wire on twenty pin plug). I bought a twenty to twenty four ATX ($3.50) power supply converter adapter. Wired on a harness to extend the original power connecter to outside the rear hole made available by removing to A. C. filter. Spliced in the twenty pin header from the ATX conversion power supply adapter. Added Molex pin for minus five volt supply (was blank), and spliced that one in. Spliced in twelve volts from ATX supply (Used four pin square Molex two yellow, two black,, salvaged 4-pin Molex mate from old MB). Recheck and power up.
Attachments: Original Failed Functions.
             Pics of new Supply inder photo'sl.
             Pic of Passed Functions under photo's
Good luck with your restore project..

If you want to see the pics, join the group and look into the Files section.

[m3vuv]

WELL,ITS SODS LAW,JUST STARTED TO MAKE AN ADAPTOR TO RETROFIT A PC ATX PSU TO THIS AND MY SOLDERING IRON HEATER ELEMENT HAS BURNT OUT/GONE OPEN,OH WELL NEW ONE ORDERED,WATCH THIS SPACE.

[m3vuv]

How critical are the 5.2v supplys in this as obiously the atx psu only has 5v outputs not 5.2,cheers Paul m3vuv.

[m3vuv]

well i have got this sort of working,it fails self tests (see pic),thing was i brought this with a dead psu and supposedly faulty nvram,i wonder if the issues i get is due to running from an atx psu,ie 5v rails as oposed too 5.2v rails,or whether the seller was dishonest ?

[m3vuv]

well with the new nvram fitted this is what i get(see pic),it wont cal either,its like the whole front end is dead.

[Runco990]

Make sure you "load defaults" first.
That is the normal dead NVRAM error.  Either replace it, or do the battery mod.

[m3vuv]

what do i have to do to load defaults,thought it did that automaticaly?

[Runco990]

Somewhere in the calibration menu should be a load defaults selection.  THEN do the calibration.

[m3vuv]

i can load the default cal values but as soon as i try to do a calibration it fails D/a and A/D converter and analog trigger same as before.

[SoundTech-LG]

Well, the Attenuators are notoriously subject to fails in these. Sometimes you occasionally get really lucky and you can "Excercise" them for long periods of time in the menu selection for 50 ohm/1MOhm input impedance. The relay contacts get oxidized enough to cause issues. Most of the time though the attenuators get a nice overload zap of voltage (user) and burn out a 50 ohm resistor, or even worse! Hard to find at any reasonable cost those attenuators...

[m3vuv]

well using the atx psu ,it mostly works apart from the self test fails,i notice tho the +/- 5v rail drops to about 4v when the cable from the psu is connected to the mainboard,i wonder if the psu isnt beefy enough or a shorted cap on the mainboard causes this,i have new caps to recap the original psu now,only no soldering iron,still waiting on royal mail delivery,its only 3 days late so far!!!!

[m3vuv]

i just hope no clicking from the anttenuator relays and the analog trigger/D/A A/D converter fails are down to the low 5.2v rails!

[Zappy]

Hello,
I have two HP 54502 and one 54510. To repair the Boschert power supply you need to replace all the electrolytic capacitors. This issue has been fixed in
https://www.eevblog.com/forum/repair/hp-53310a-power-supply-troubles/msg934342/#msg934342

It will take some time to do it but you'll get a full working supply after that.
Fact is that there is a crowbar to protect its hardware. The SCR is triggered by some voltages unbalance. Regulation is done on the +5V only as the schematics shows. Someone has tried to replace it with standard MEANWELL PSUs. He finally let it down, results were not good.