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Full Version: HP-97S with a bad BCD interface: help me!
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Hi All,
I'm looking for a little big help with a not working BCD interface. I have tested it with the Test connector and the test program. Nothing is happened, the program stop at line 005 LBL A waiting a response from the interface.
Who can give me an help?

The pod for the 97S has 50 or so 4000 series CMOS chips in it, it's possible one or more of them are bad -- I've seen this happen in one case in particular All of these chips except one ROM are still readily available for purchase and they are very inexpensive.

The 97S manual has a partial schematic of the pod which will help in debugging, but in working with a friend of mine we decided to pull all the chips (i.e., de-solder them) and test them in a handi-dandy IC tester I have. We were able to find the bad chips and replace them pretty easily.

You can find some of the 4000 series part numbers cross referenced to the HP part number here.

Better still, here's an almost complete cross reference list of the IC's used in the 97S pod from my notes:

1820-0927 4028
1820-0936 4024
1820-0938 4027
1820-0939 4013
1820-0946 4001
1820-0949 4011
1820-1114 4516
1820-1145 4049
1820-1466 4017
1820-1483 4071
1820-1485 74C221(?)
1820-1665 4099
1820-2037 4081
1820-2080 4035
1820-1518 4076
1820-1408 4073
MC14043B 4043 (obviously)
MC14512 4512 (obviously)

If you want to debug by tracing signals you should get a hold of Tony Duell's hand drawn schematics for the 97s pod, that will help a lot.


Edited: 21 Mar 2011, 8:34 p.m.

Hi Katie,
I have another BCD interface and I have swapped the upper PCB to test where is the issue: this is the bad PCB. Thanks a lot for the great info about the cross reference, I hope to find the spare parts to replace the chip step by step.

Regards from Italy and thanks again


Having a working 97S i/o pod is a big help!

Here's a great place for old and obsolete parts: Unicorn Electronics.

I'm sure that they have all the 4000 IC's you'll need. However, I'm not sure if they'll ship outside the US.

BTW, the IC tester that I have is a clone of this. It's been around for a long time and has been cloned several times. If you look around you may find it for not much money at all.