Cleanup and mechanical repairs on a 1996 vintage HP 1662C Logic Analyzer to add to my test equipment collection.

This one was an Ebay auction purchase that started at a very low initial bid price. There were three other bidders on this auction, and it went significantly lower than my maximum price I was willing to pay for this item.
The listing said that it had been “Power Tested, and is being sold as is”, whatever that is supposed to mean.
There was a picture of the analyzer configuration screen, but nothing that showed the startup self-test status screen. So I knew that it was a bit of a gamble if there were any other issues with this unit, which also probably helped to keep the cost low.
At least I knew that the monitor powered up, and displayed an image.

When the unit arrived I checked it over for exterior damage, and noticed that the aluminum case where the back plastic feet attached was dented in from some rough handling in the past.
While the packaging of the unit wasn’t perfect, it didn’t receive it’s dents from this shipment. The plastic trim piece around the front bezel was fairly beat up with lots of cracks, and broken sections at the screw mounting points.
After removing all the screws, handle, feet, and back bumpers it was time to pull the case off. That took a bit more effort than I thought it would as the dented case areas were preventing the case it from sliding off, and required some extra effort using flat blade screwdrivers to slowly wedge the case off, while partially straitening the dents.

The unit was remarkably clean inside, with a very small amount of dust present. An initial inspection of the boards showed no visual signs of faulty or damaged components.
I did want to inspect the power supply before powering up the system for the first time though.

To gain access to the power supply the floppy disk and hard drive assembly needs to be removed. This is easy and requires removal of two screws from the sides of the bracket that holds the floppy drive. The assembly slides forward which releases the back tab from the frame, which allows it to be lifted and then slid back to remove the assembly.

Once the drive assembly is removed there are two plastic pins with triangular flags that need to be removed. These slide straight up and release the power supply and CPU board. There are two cables connected to the supply, AC power in, and DC power out, that need to be removed before sliding the power supply out the side.
I had a bit of difficulty sliding the supply out as the aluminum tab had been deformed, probably caused by the same impact that dented the rear case feet.


The power supply cover is attached with 17 screws; no chance of it accidently falling off.
In it were Nichicon and Rubycon capacitors, which were all in good condition. After using some compressed air, and some quick in-circuit capacitor checks, I reattached the top cover.
There is one external adjustment between the two connectors for the power supply 5 volt rail and associated test points for ground and +5 volts DC.

Located below the power supply is the A2 CPU board with it’s 8 connectors and removable SIMM memory module. It uses a Motorola 68EC020 with a 32 bit data bus and 24 bit address bus, running at 25 MHz. this is the same processor used in the Amiga 1200 computer and the Amiga CD32 game console. There are four 512Kx8 Flash ROMS which are configured to provide a 512Kx32 Flash ROM space, and a single 128Kx8 boot EPROM.

The internal frame of the logic analyzer is a cast aluminum structure which includes a slotted card cage area which supports the A2 CPU board, A9 power supply, and MP2 disk drive bracket. There is a 12 volt system fan on the back of the card cage, which forces air thru the cage area and then thru the rest of the unit exiting the rear panel perforations.

The HP 1662C supports 64 data channels and 4 clock channels which can also be used as data channels if needed. Basically the board is the same as the 1660C 136 channel system with half of the acquisition board input IC’s and connectors unpopulated.

The front panel power switch is connected to the back panel power entry module with a flexible cable, and switches power directly at the module. The power entry module has a C14 male IEC power connector, along with a voltage selection and fuse module, and a RFI/EMI filter.

The back panel has a lot going on, and includes connectors for HPIB, RS232 serial, parallel printer, keyboard, mouse, power, Pod 1&2, Pod 3&4, External trigger output, and External trigger input connectors. Much of the back panel space is taken up with the fan air intake grill, and perforated air exhaust area. There four plastic legs which extend from the back of the unit to help protect the Pod connectors during use and transport.

The unit came with a E2433 “Credit Card Board” which is part of the training kit for this series of logic analyzers. It generates an 8‑bit ripple counter test pattern on 8 data channels, along with clock and glitch outputs. It connects directly to a Pod cable and includes built in probing termination.

A screen capture of the outputs from the Credit Card Board connected to my HP 1662C.

After testing the functionality of the logic analyzer, I decided to update the Flash ROM to the latest version on the HP/Agilent/Keysight website to version 2.01.
After downloading the software and preparing the floppy disks, it was time to perform the update, which is quite a scary task as it starts with erasing the Flash ROM before verifying that it can actually fully read the floppy disk.
Everything worked perfectly though, and I was now using the latest firmware version.
Along with the firmware, the download also included the updated system test software, and the Symbol utility software module.
After trying to load the Symbol utility, I was getting cryptic messages about loading failures. It seems that this is caused by insufficient System RAM memory.



My system came standard with 2 MB of Flash ROM and 2 MB of System RAM, so I purchased a 8 MB stick of 72 pin EDO memory PN 1818–5623 which was listed as “required with LAN option” in the service manual. I didn’t have the LAN option, but after upgrading the RAM the system now loads the Symbol utility, with no errors.

I decided for my first probing attempt I would try to use the logic analyzer on my HP 34740A Display using the updated HP 11456A Read Out Test Card that I built.
I was able to purchase a new HP Pod 1 Data + J Clock Cable Set on Ebay, since my unit was missing that accessory when I acquired it. It provided the proper termination on the Pod cable, and included the mini grabbers to connect to the test card.


This would have made troubleshooting the HP 34740A display so much easier, and saved so much time. The only downside to using the logic analyzer is the time it takes to setup the probes, and the time it takes to setup and configure the logic analyzer itself. The use of an external keyboard and mouse does help to speed up the process though. Once the system is configured it is easy to save the configuration to either the hard disk or floppy for working on the same model in the future.
I am currently designing a board for connecting an 80C52 CPU system to the 1662C logic analyzer using direct connection of the Pod 1&2 cables to the test board, and providing the needed termination on the board. This should also work for other 8052 series of CPU’s such as the 8031.
A big Thanks! to all the “Buy Me a Coffee” supporters who helped make this purchase possible.