Originally posted in December, 2018

Early in 2018, I purchased an HP 3562A Dynamic Signal Analyzer for an excellent price on Ebay. The display looked great and it was physically in good condition. However, the unit failed the power on self test as follows:

This error code indicates a ROM IC failure.

HP3562A Diagnostic LED’s indicate Hex code 4 4 (0100 0100). Referencing the Service Manual, this code indicates a failure of ROM Chip U105:

This ROM board is an older version using 32kx8 chips in two groups (Low Byte & High Byte) of 18 chips each. I had access to a second 3562A, and swapping ROM boards confirmed that the ROM board was the problem. Now I needed to:

• Locate a suitable set of ROM images
• Purchase a replacement ROM
• Desolder the defective ROM
• Burn and test the new ROM
• Solder in a socket and install the new ROM
• Test the 3562A

I am indebted and grateful for the help of Dr. Simon Schroedle, who not only sent me a complete set of ROM images, but confirmed my diagnosis of the problem. He also pointed out a few pitfalls which one could encounter when replacing the ROM chips.

Simon has a superb weblog where he documents his diagnosis and repair of HP and other test gear: http://www.simonsdialogs.com/

I carefully desoldered the defective ROM chip using solder wick and a chisel tip iron. (I have since refurbished a Hako 472D desoldering station which has made subsequent desoldering work faster and safer.) The ROM board was cleaned up and a new socket was soldered in. I purchased several Atmel AT27C256R 32kx8 EEPROM chips from Mouser (<$2 each), burned and verified the appropriated ROM image, and installed the ROM board back into the 3562A. Here is the result:

The Powerup Self Test Passed, and the Service Tests also passed:

The Fault Log was clear:

I completed the repair process by rechecking all the power supply voltages for both magnitude and ripple. The unit has been working well since I repaired it and I have been learning how to use its many and varied functions.

Additional notes:

• It is essential to obtain the correct HP service manual that covers the serial number of your particular instrument.  The circuit and component differences between product runs (comprising different serial numbers are significant.
• In doing this type of work, a vacuum desoldering setup is indispensable.  I have used my Hako 472D many dozens of times since purchasing it in 2019.