Fixing Up a Hewlett Packard 1662C Logic Analyzer

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

HP 1662C Logic Analyzer after some cleaning

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.

HP 1662C Configuration External I/O screen w/keyboard & mouse

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.

HP 1662C A13 Monitor board and CRT

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.

HP 1662C bot­tom of the Floppy and Hard dri­ve brack­et assembly

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.

HP 1662C — 545 Mb Quantum Hard drive

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.

HP 1662C A9 Power sup­ply with top cov­er removed
HP 1662C A9 Power sup­ply con­nec­tor side view with top cov­er removed

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.

HP 1662C A9 Power sup­ply labels

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.

HP 1662C A2 CPU board

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.

HP 1662C Cage for Power sup­ply, CPU board, and dri­ve assembly

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.

HP 1662C CRT yoke assy. and acqui­si­tion board below

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.

HP 1662C Power input, fuse, fil­ter, switch, and volt­age selec­tion module

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.

HP 1662C Back pan­el with POD 3 & 4 cable attached

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.

HP E2433 Credit Card Board Rev A train­ing card

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

HP 1662C Print screen using the train­ing cred­it card

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.

HP 1662C Basic self-test start­up screen
HP 1662C Extended PV test sys­tem “PASSED” screen
HP 1662C after firmware upgrade with orig­i­nal sys­tem RAM

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.

Upgraded 8 MB System RAM on A2 CPU board

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.

Probing the HP 3470A with the HP 1662C Logic Analyzer Pod 1
HP 1662C wave­form dis­play of the HP 34740A Display module

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.

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