Author Topic: Keithley 2304A high speed power supply (Read 21100 times)

Short Circuit · « **on:** February 15, 2012, 06:34:21 pm »

This afternoon, I finally made some time to modify my Keithley 2304A power supply.
The power supply is extremely noisy, which made it too annoying for regular use. Also, it has screw
terminals on the back for the connections, not very convenient for general lab usage.

So I bought a new Sunon fan and a couple of banana jacks with 'switch' function (jacks with two half
terminals inside, which are shorted when a plug is inserted).

The machine contains a surprisingly large amount of electronics; two 20x29cm boards full of control
and power electronics, and a small user-interface board to control the LCD and keys.

Short Circuit · « **Reply #1 on:** February 15, 2012, 06:37:38 pm »

...and closeup of the modifications.

Nice high-accuracy meters in this machine;
no connections shows a current of -0.0005mA (it's a 4-quadrant PSU, so current can be nagative, and in this case, it needs a bit of calibration)
with my Fluke 189 connected, load is increased to +0.0009mA

alm · « **Reply #2 on:** February 15, 2012, 07:42:25 pm »

Nice piece of equipment, and some professional looking modifications. Are all those caps in the second picture (top PCB) in parallel?

Short Circuit · « **Reply #3 on:** February 15, 2012, 08:34:58 pm »

Yes indeed, 40 mlcc's all parallel, and only 36.6uF... Seems highcap mlcc's were not so common when this PSU
was designed in 1997 (copyright notice on the PCB).

That makes this a 15 year old device, yet the very same model is still available new from Keithley. Not bad.

muvideo · « **Reply #4 on:** February 15, 2012, 08:37:41 pm »

Wonderful power supply, alm also my eye immediately was attracted by that huge ceramic capacitors bank.
Also it's impressive the meter resolution of 100nA, 14V in 10Mohm is 1.4uA and it shows 0,9uA+0,5uAoffset=1,4uA!

Fabio.

Mechatrommer · « **Reply #5 on:** February 15, 2012, 11:34:38 pm »

Quote

Keithley 2304A high speed power supply
The power supply is extremely noisy

what it means by high speed? ho high? 100MHz? 1GHz?
why this branded psu with alot of electronics is extremely noisy?

Jad.z · « **Reply #6 on:** February 16, 2012, 12:11:03 am »

Hi Short Circuit

This is a nice unit indeed. I actually have one of this laying around the lab collecting dust.
One day it just quitted at me. Unfortunately, I never had the time to fix it nor the willing to debug a (0.12 m^2) of circuitry

@Mechatrommer

Here is what the datasheet says:

TRANSIENT RESPONSE TO 1000% LOAD CHANGE:
NORMAL MODE:
Transient Recovery Time:
<50us to within 100mV of previous level.
<100us to within 20mV of previous level.
ENHANCED MODE:
Transient Recovery Time:
<40us to within 100mV of previous level.
<80us to within 20mV of previous level.

BTW, does anyone have the schematic for this one or the service manual please. I searched everywhere and I just can't find it

Short Circuit · « **Reply #7 on:** February 16, 2012, 12:45:15 am »

I have no idea about the noise characteristics of this power supply, but that's not important either.
This machine is designed to simulate batteries for GSM test & development purposes. Cell phones
tend to switch from very low standby current to 2Amp RF TX pulses. A normal PSU simply collapses
under such load change because the load transient response is not fast enough.

Personally I use the machine for R&D on systems that flip between normal operation with load current
up to few amps and standby current in the mA range. The nice thing abou this PSU is the very accurate
5mA current sense range without limiting the load capacity. With a normal amp-meter you must
arrange to stay in either range because of the voltage drop across the load-sense resistor, which
makes it impossible to jump from 1mA to 1A without goofing around with jumper cables to bypass
the mA meter.

Jad.Z; have you tried asking your local Keithley representative? I found them very helpful when I
asked them for spareparts of this PSU. I bought it from eBay being an ex-rackmount device, so there
were no handles and feet included. It was no problem at all to buy these, costing a mere 25 euro or
thereabout. (Although perhaps it helped being a customer already, as I cannot believe they would
create a customer account for only 25 of spare parts.)

saturation · « **Reply #8 on:** February 17, 2012, 09:49:58 pm »

It has great specs; it has linear like stability with digital controls. The eBay price is near $1000.

Short Circuit · « **Reply #9 on:** February 18, 2012, 03:14:24 am »

That are trader prices. Normal auction price can be much more reasonable; I paid $400 for it.

Mechatrommer · « **Reply #10 on:** February 18, 2012, 03:40:24 am »

Quote from: saturation on February 17, 2012, 09:49:58 pm

It has great specs; it has linear like stability with digital controls. The eBay price is near $1000.

Quote

why this branded psu with alot of electronics is extremely noisy?

now i get it. mixed smps + linear psu tech, thats why more electronics i guess. i've been (currently) eyeing this kind of topology.

saturation · « **Reply #11 on:** February 18, 2012, 01:54:28 pm »

Yes, it has the best of both worlds, but I didn't read too much into it, before going this direction with a PSU it helps to confirm:

You can series or parallel it with another capable PSU without issue, to get more volts or amps .. very flexible and preferred, many cheap linear PSU can do this easily but I don't know if they can respond as quickly as this PSU

Its user repairable: the controller circuitry of the Keithley looks like a lot of work to repair if damaged

Quote from: Mechatrommer on February 18, 2012, 03:40:24 am

Quote from: saturation on February 17, 2012, 09:49:58 pm
It has great specs; it has linear like stability with digital controls. The eBay price is near $1000.
Quote
why this branded psu with alot of electronics is extremely noisy?
now i get it. mixed smps + linear psu tech, thats why more electronics i guess. i've been (currently) eyeing this kind of topology.

SeanB · « **Reply #12 on:** February 19, 2012, 12:21:54 pm »

Those mains powered fans are easy to fix, they normally only need a few drops of engine oil on the bearing and then they run for years again. After a few years of continuous operation the sleeve bearings will wear out, but the oil normally evaporates before this. A drop or three and away it goes.

wlanfox · « **Reply #13 on:** May 17, 2015, 10:31:11 am »

I just acquire one of this very nice power supply / source (can also be use as a constant source )

... Does anyone know what that J13 header is for? JTAG, SERIAL, other? try looking for the service manual but so far I have come up empty...

reagle · « **Reply #14 on:** August 25, 2015, 03:12:39 pm »

Just grabbed one of these as well. One of the MLCC in the large parallel group is completely burned. Looking around, nothing else seems unhappy- I presume it just happened to go on its own?

TheBay · « **Reply #15 on:** August 27, 2015, 09:38:58 am »

Wow lovely PSU!,

Get some Retrobrite on it

eas · « **Reply #16 on:** August 27, 2015, 06:17:52 pm »

I snagged one of these for ~$100 a month or so ago. It looks like someone stabbed through the clear section of the plastic sheet over the display with an Exacto knife, but is in good shape otherwise.

I have a home server with picoPSU + 12v power brick for quiet operation. The 12v brick died after a bit over a year. I didn't have a suitable replacement, so I ran it off the 2304A for a few days. The thing is freaking LOUD. I'll need to do a fan retrofit if I keep it.

reagle · « **Reply #17 on:** September 18, 2015, 02:11:44 am »

Mine was a cool $75 on ebay, plus a few "extra" parts I bought to "pimp it out".
Ended up adding binding posts on the front, as the terminal block on the back is not optimal for bench use. Then I got fed up with a low contrast and poor viewing angle of the original yellow LCD display and swapped it for a modern drop in replacement. Ended up having to add a potentiometer to adjust contrast voltage as well.
I was really hoping to find an OLED one, but geometry and pinouts did not align. So I used this simple negative LCD (ERM1602SBS-3 from BuyDisplay). The pinout and mechanicals fit nicely, I just had to flip backlight polarity jumpers

Magnum · « **Reply #18 on:** October 03, 2015, 10:41:01 am »

I replaced the fan of my 2304A to lower the noise.
Keithley placed a very big component directly in front of the fan and that makes a horrible high frequency noise due to air turbulence. The original one is 25mm thick, I used now a 20mm thick fan with the same airflow. The noise was reduced by more than 3dB, and all the high frequency noise is gone. It is still not quiet, but that is because of the high airflow. If you want to live with higher temperatures inside the unit you can reduce the noise further, just remember to use a thinner fan.

The one I used: Sunon MB 60202 V1-000U-A99
available from http://www.elpro.org for 3,79 EUR

mrjoda · « **Reply #19 on:** July 07, 2017, 11:34:25 am »

hi guys, i bought 2304A few day ago from ebay.de for 150€ shipped. Inside looks clean, some particle of dust but nothing hardcore. I clean it.

I noticed a little mod board marked as Keithley wired to DG408 and glued with double sided tape. Do you know why ?

Voltage looks good, can be set up, current also. Device switch between CC/CV without issue. Only thing i notice is little chirp noise from inside, no matter if is loaded or not. I try to record it. I will try to find source, maybe is it only bearings inside FAN, maybe is it something more serious.

Is it neccesary to change electrolytic caps ? they are nichicon/nippon chemicon but device is marked 1997 so they are 20 years old.

here is video. I dont know if you will hear it but i can.

https://youtu.be/G78v_7z-M18

here is another vid. Is it definetly from main power supply
https://youtu.be/bdmQ3gakizU

edit :

i try to push components with plastic marker, same pitch. I measured all voltages on testpoints - all correct and stable.

alm · « **Reply #20 on:** July 07, 2017, 04:37:12 pm »

I have not heard of any of these units having leaking electrolytics. They seem to have used good quality caps and not overheated them. So I see no pressing need to start shotgunning all electrolytics unless they are showing signs of leakage or increased ESR.

The chirp could be coil whine. Making sure all screws are tight might help a bit.

mrjoda · « **Reply #21 on:** September 10, 2017, 02:02:21 pm »

so i finally did some scratch repair and i replaced fan for Sunon MB 60202 V1-000U-A99 (from Magnum post). Is it still noisy but i can live with that noise level. I think about pulling out two leds for ON/OFF status and CV/CC for better readability. There are some testpoints on board marked as OVER-I, maybe it will be possible to use it for led indicator.

I repaired scratches with some wierd clamp but it works perfect. Heatgun + clamp and scratches disappeared.

macboy · « **Reply #22 on:** September 12, 2017, 05:18:33 pm »

I've effectively repaired dings like that with just hot air. The ABS plastic has an amazing shape memory. The trick is to use just the right temperature, so that the plastic softens enough to go back to original shape, but doesn't melt (and lose its memory). I've also repaired various LEGO parts (also ABS) with the same technique after my boys bent, chewed or abused them. It's amazing how much deformation can be reversed this way. Pro tip: experiment with temperature and technique on LEGO bricks before moving on to big-$$$ equipment.

bitseeker · « **Reply #23 on:** September 13, 2017, 02:15:32 am »

Good to see that heat works OK. I've got a 2700 with a dinged corner, but was reluctant to have a go with the heat gun.

TheSteve · « **Reply #24 on:** September 13, 2017, 03:29:49 am »

Careful application of heat does work wonders. I have before/after pictures of an Agilent 33250A that had pretty crazy damage posted somewhere here.


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Author Topic: Keithley 2304A high speed power supply (Read 21100 times)

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