Intro

Some good 7 years ago I have bought and repaired SMU, legendary industry standard Keithley 2400. It served very well on the bench, helping with countless number of repairs and projects. Model 2400 able to supply voltages and currents with power envelope up to 20 Watts. However sometimes there is need for a little more power, and for that a different variants of Model 24** series are offered by Keithley (today part of Tektronix). One of such variant is Keithley 2425, which is 100W SMU with boosted current 3A output range, while still supporting 100VDC output range for lower currents.

Image 1: Power envelope of Keithley 2425

It is previous generation device, replaced today by fancy Keithley 2460 with even higher capability.

In this article we will look into three different Keithley 2425s and try to restore them to glory, perform calibration and performance verification.

Manuals

Keithley 2425 100W Service manual

Keithley 2425 Specifications

Keithley 2425 Datasheet

Troubleshooting and repair of unit 1

Video about this unit repair available as well.

Troubleshooting and repair of unit 2

Video about this unit is here:

After milling damaged carbonized PCB material around burned mosfet pads area got cleaned.

New IRFI540N transistor was installed and reconnected to GND, transformer winding copper trace on inner layer and gate drive from series 475 Ω resistor.

After checking proper operation affected area on PCB was sealed again with special green soldermask epoxy liquid and left to cure for few days. This will further protect the exposed copper on PCB cut area and prevent moisture ingress any further.

Troubleshooting and repair of unit 3

TBD.

Firmware and undocumented features

Firmware

Here are some firmware dumps for Keithley 2400 series SMUs. Firmware is universal across series and same on different instruments:

• Keithley Model 2400
• Keithley Model 2410
• Keithley Model 2420
• Keithley Model 2425
• Keithley Model 2430
• Keithley Model 2440
• Keithley Model 2400-C
• Keithley Model 2410-C
• Keithley Model 2420-C
• Keithley Model 2425-C
• Keithley Model 2430-C
• Keithley Model 2440-C

Firmware version	Combined binary	ODD ROM	EVEN ROM	Original SREC + Release notes
Model 24XX C06 Version 51.1, Dec 16 14:52:35 EST 1996	24XX Full binary			SREC
Model 24XX C10 Version 62.1, Jun 4 13:53:13 EDT 1997	24XX Full binary	2400-803-C10 ODD ROM	2400-804-C10 EVEN ROM
Model 24XX C30 Version 192.1, Mar 17 09:28:23 EST 2006	24XX Full binary			SREC ZIP
Model 24XX C32 Version 199.1, Oct 4 14:19:20 EDT 2010	24XX Full binary	2400-803-C32 ODD ROM	2400-804-C32 EVEN ROM	SREC ZIP
Model 24XX C33 Version 201.1, Mar 31 09:31:47 EST 2015	24XX Full binary	2400-803-C33 ODD ROM	2400-804-C33 EVEN ROM	SREC ZIP
Model 24XX C34 Version Dec 6, 2016				SREC ZIP Release notes

Version C33 fixes the issue of powering up with a low line-voltage (90 volts in Japan) for models 2420, 2425, 2430, 2440. Upgrading to this version of firmware will add a 5-second delay to power-up for all models running it.

There are also two D-firmware versions available for newest Keithley 2400 and 2410 hardware.

Do NOT flash D-firmware onto unit that is running any B or C version firmware. This will ruin the instrument due to different digital board hardware!

Firmware version	Combined binary	ODD ROM	EVEN ROM	Original SREC + Release notes
Model 24XX D01 October 7, 2020				SREC ZIP Release notes
Model 24XX D02 February 11, 2021				SREC ZIP Release notes

Also here’s Python app to generate EVEN+ODD ROMs from full little-endian binary file, just in case someone need it.

# xDevs.com Firmware combine tool 
# https://xdevs.com/fix/kei2400

import os

with open('2400c32.bin','rb') as a:
    with open('2400-804-C32.bin','wb') as bf, open('2400-803-C32.bin','wb') as cf:
            for cnt in range(0, 262144):
                bf.write ("%s" % a.read(1) ) 
                cf.write ("%s" % a.read(1) )

It takes input binary and prints it into two files output. Opposite application to combine split files into single little-endian binary available as well.

Also due to safety reasons self-diagnostic procedures and functional self-tests are hidden and must be accessed in unlocked secret mode. This was shown before here but for clarity will duplicate information here as well. On 2400 series SMUs entering secret mode is done by two buttons:

1. Ensure unit is powered off.
2. Press and hold gray button "^" and button "SWEEP" and power on unit
3. Secret menu available now in MENU/GENERAL/SECRET
4. After power down unit enters normal operation mode as usual.

Here are hidden menu items on Model 2400 with firmware C32:

Menu item	Detail	Default	Note
MODEL#	Override model ID		Allow to force ID to 2400/2410/2420/2430/2426/xxxx. Warning! Calibration will be LOST!
FB-BURN-IN	Burn-in all VFD pixels
DIGITAL-REV	Write digital board revision ID into ROM		Stores digital board revision in calibration ROM
ANALOG-REV	Write analog board revision ID into ROM		Stores digital board revision in calibration ROM
CONTACT	Enable contact option 24xx-C(need hw)		Allow to enable CONTACT option hardware

Of course, changing MODEL ID will not make SMU working with other ranges, since analog boards on different models within 24xx series are physically different.
This function is in firmware to allow developers test and use same digital board and same firmware, while connected to different analog boards.

Do not change Model# if you don’t have calibration-grade DMM, standards and calibration knowledge available! Instrument calibration data will be permamently erased and lost!

Calibration

TBD.

Benchmarks

TBD.

Conclusion