Interesting chipset. I have no idea what is this, but the build quality is sort of very high quality one. See the traces on the PCB also.

This module has its own serial number 03561-66530. We can see 14-pins DIP IC made from El Salvador. I have seen some from Malaysia, Singapore, Taiwan, Portugal, and other countries on this machine. Seems like really multinational collaboration?

I believe this “bat” logo means Motorola? This one should be microprocessor/micro-controller from Motorola. One of the main brain of this machine for sure.

This 03561-66540 should be the processor module. I suspect that because we can see the main Motorola CPU there (1820-2505) which should be Motorola 68000 processor. Also several big EPROM chips also located in this module.

This is one of the bigger damage found in this machine. One (or two) of the EPROM is damaged due to the poor handling of the shipping company (not to mention the poor packaging from the seller also).

The EPROM is D27128-3 which is UV Erasable PROM. It will be very difficult to find replacement. The worst, I need to get a complete 03561-66540.

Do let me know if you know where to find this replacement module (03561-66540).

Appreciate also if someone can help me with the replacement EPROM (D27128-3). Finding the EPROM is easy, but to program it with correct data segment would need a very big luck!

Not quite sure about the next board (03561-66550). But it also consists of several ICs and EPROMs.

There are some parts on this module (03561-66550) which covered with thin metal plate. I suspect the function is to shield the components underneath the cover from external interference. Could be a very sensitive components there?

This module is very simple, 03561-66560. Nothing really special on this module. Only consists of DIP ICs, a lot of them.

Next is one of the power supply board. There is a 3 Volts Lithium Cell. Not quite sure if this can last for 30+ years?

Next is what I call a ground plane. Have no idea what is this for. But seeing such large copper pour there, it must be carry some very important function there.

After several hours disassembling the HP Agilent 3561A, finally I need to assembly it back to original condition. I have no plan to power it up until I could find the replacement module of 03561-66540 or replacement EPROM (D27128-3). I know that would need a miracle to find a working module to replace the defective one (not mentioning the other damage during transit), but I’m quite confident I could resurrect this HP Agilent 3561A someday…

If you happen to know any help related with this problem, kindly drop me an email to below address.