|Re: Different HP-71Bs|
Message #4 Posted by Tony Duell on 27 Apr 2005, 3:11 p.m.,
in response to message #1 by Matthias
I have an HP71 service manual... I also have fixed a fair few of them...
Now, to comment on your machines. The lower one is a fairly normal late-production version with the zerbra strip between the 2 PCBs. Most have the 2CDCC ROMs. This is the rarer version in the UK, most were more like the upper one.
I was going to say your upper one was a standard early-producion model. But it's not. Look at the memory hybrids (lower PCB, between the plug-in ports). Production machines, either version, have 4 off 4K RAM hybrids and 1 off 64K ROM hybrid. You only have 1 hybrid. And you have the (white) jumper to the left of them. This is shown in the service manual schematics, but never commented on. However, it's clear what it does, it completes the configuration chain (this will make sense if you know the saturn bus hardware) if you only have one RAM hybrid fitted. It appears there was going to be a 4K RAM version, which AFAIK never went into production. I wonder if you've found one!
Now, with 1 hybrid, you either have just RAM, or just ROM, I think. This may be why your machine doesn't work. RAM is entirely soft-configured, it would therefore be worth sticking a 4K RAM module into one of the front ports and seeing what happens. More likely, though, it's the ROM that's not present. This may have been a development machine for testing ROM code from an external emulator box or something.
I will see if I can find the numbers of your hybrids in my service manual. I am a little puzzled that you claim all 5 hybrids in your later machine are the same. I am sure one is 'odd', being the ROM.
FWIW, the 71 was orignally going to be called the HP44, I think. I've seen documentation mentioning it by that number.