Restoring a HP9830B calculator.

[MattisLind]

Hello all!

I am about to start a restoration project to restore our HP9830B calculator. It is quite dirty exterior wise. But looks OK on the inside. This machine includes a printer and two 7900 disk drives and a controller. It seems that once upon a time it has been used for accounting since we have function key templates which indicate so.

The problem is that four keys are broken off and that that three key tops are missing. Those are "DELETE LINE", "END", and "5". I have been told that HP264X terminal use the same key tops. But those don't have the "DELETE LINE" nor "END" keys, only the "5".

Does anyone have spare key tops to sell? Does anyone have have those Cherry key switches? Maybe it is possible to repair them by melting in some metal into the upper part. But I haven' tried yet.


By the way, does anyone know the Cherry model name for these switches so I can start search around for it?

Next step is to dig into the power supply and check capacitors.

All help greatly appreciated!

[waterlander2004]

Hi Mattis,

Good to see another 9830 enthusiast!

I do happen to have a couple of extra keycaps. At least I have a 'delete line' and a '5' key cap. I assume you need the '5' that belongs in the numeric block, correct? Just send me a mail with your details.

With respect to technical info, you'll find an excellent source in the 98xx repair guides written by Tony Duell, published in the HPCC DataFile. If you're not yet a member, these guides alone would make it worth becoming one.

Keep us posted with your restoration progress!

Kind regards, Eric

[Tony Duell]

The Cherry switches were a standard part, in that I found an non-HP keyboard that used them. I have a few (very few) spares somewhere, hopefully they will turn up sometime...

As regards getting the machine going, in my experience power supply problems are uncommon, and I've yet to replace a capacitor in the PSU of any HP9800 machine. But logic problems are common. Most of the time the display is totally blank and the fault is somewhere in the CPU/memory control section. A logic analyser is very useful.

Good luck with the HP9880 disk system. This is going to be one of my next projects, I have all the bits of one now...

Let me know if I can be of any help.

[MattisLind]

(04-25-2014 06:23 PM)waterlander2004 Wrote:  Hi Mattis,

Good to see another 9830 enthusiast!

I do happen to have a couple of extra keycaps. At least I have a 'delete line' and a '5' key cap. I assume you need the '5' that belongs in the numeric block, correct? Just send me a mail with your details.

With respect to technical info, you'll find an excellent source in the 98xx repair guides written by Tony Duell, published in the HPCC DataFile. If you're not yet a member, these guides alone would make it worth becoming one.

Keep us posted with your restoration progress!

Kind regards, Eric

Hi Eric!

The five is the "5 %" key, not the numeric block. But I did find someone at Ebay selling key tops from what I presume is the keyboard of a HP 2648 which AFAIK is pretty much the same . I bought them... That included the "5 %" key top. But the END and DELETE LINE keys are obviously not in that set. But now I have a set of other key tops if any one needs!

I send you a PM regarding the "DELETE LINE".

Tony Duell Wrote:The Cherry switches were a standard part, in that I found an non-HP keyboard that used them. I have a few (very few) spares somewhere, hopefully they will turn up sometime...

I searched google (and ebay) high and low trying to figure out what kind of model this is but didn't found anything.

Tony Duell Wrote:As regards getting the machine going, in my experience power supply problems are uncommon, and I've yet to replace a capacitor in the PSU of any HP9800 machine. But logic problems are common. Most of the time the display is totally blank and the fault is somewhere in the CPU/memory control section. A logic analyser is very useful.

Good luck with the HP9880 disk system. This is going to be one of my next projects, I have all the bits of one now...

Good to know about the PS. I do have a logic analyser. Only 32 channels though.
I'll have a look in the repair files. It will probably be quite a while until I start looking at the disk sub system.

I'll update the thread when there are progress (or problems are arising...)

[MattisLind]

Well. I just tried to repair the broken Cherry switch. I bought some piano wire and bent it into a small U. Then I used a soldering iron to heat it up while slowly pressing it into the plastic of the key switch. It didn't came out 100 % exact. It seems to be off by half a millimeter from the centre. But to me it is good enough. It feels very stable and won't certainly break that easy. Three more to go!

[MattisLind]

Working!

At least I think most of it is working!

Here is the story anyway:

I contacted Tony and received his excellent repair guide for HP98x0 calculators. (His file is in postscript, and is rather small but I converted it to PDF for ease of viewing, then it became huge.) I also downloaded Tony's schematics. While searching the net for HP9830 related material I also found Brent's excellent page on the HP9830 and this HP9830 emulator.

Thanks to Erik I now have the missing DELETE LINE key, thank you very much! BTW. I have spare key tops from a HP2648 keyboard if anyone need keys for a HP9830 (or a HP2648...). Missing only the "5/%" key and one SHIFT. Slightly yellowed though.

Now on to the restoration. After cleaning the unit from plenty of dust I went on following the guide Tony has written, starting testing the insulation of the transformer using a megger. No problems at all. Then (with all cards pulled out except for the PSU module) I powered it up slowly using a variac. Measuring the voltages at the PSU output they all checked OK. But it appears that the +5V switcher need to have some minimum load as well as the 19.5 V output. The latter I would have discovered if I had studied the schematics before I applied power. The 19.5 is generated by a power source circuit and thus will give full raw voltage if not loaded. A 1kOhm resistor did the trick here and using the ROM backplane as dummy load made the 5V produce 5.01V. Since the 19.5V is slaving of the 16 V using a zener, without load on the 19.5V the 16V output started to rise. I presume that eventually the crowbar circuit would hit in, but I never got that far as I used a variac.

Well, with all voltages measuring correctly I just inserted all cards and hit the power on button. I was quite amazed that I got this:

and after pressing random key and finding ENTER I got this:


In a way it was disappointing since I sort of hoped for an interesting journey to repair it... Maybe this shows the quality of old HP products. (My modern HP work PC had the PSU break down after two years. Of course it was just relabeled Chinese stuff inside) The only thing I immediately recognized as failing was the power on indicator in the front.

Of course I haven't tried much yet. Not the tape driver, not the printer interface nor the ROM modules.

Right now I need to assemble the keyboard, then the whole unit.

[waterlander2004]

Well done Mattis, congratulations with the result so far!

[MattisLind]

I think I need to show how the internals of the HP9830 look like so I made this composite image of all the boards inside. Aren't they beautiful?

Cards all gold-plated. Fantastic! This is pure quality!



First and second row is the memory subsystem with the DRAM memory board based on TMS4060 4k NMOS chips. Third row is the cassette and display interface. Fourth row is the actual CPU. Fifth row is the display and PSU. The only difference AFAIK between HP9830A and HP9830B is the memory board (second row left) and the memory address board (top left)

[MattisLind]

Today I received five key switches and the last missing key top from a fellow HP9830 collector. Thank you very much! This is the reassembled complete working keyboard:



I tried the REWIND button. But there were nothing but a spinning sound. No motion. I think that there should be a clicking sound from the solenoids. Either there is some fault or they were just stuck.

When I looked into the tape unit I found that the rubber on the wheels were quite worn, so I need to fix that.

[Tony Duell]

(05-23-2014 08:26 PM)MattisLind Wrote:  The only difference AFAIK between HP9830A and HP9830B is the memory board (second row left) and the memory address board (top left)

That would make sense. The 9830A uses the 1K*1 DRAMs (1103), the 9830B seems to use 4K*1 DRAM chips. Unlike the 9810/9820, the level converters (TTL <-> 16V PMOS) are on the RAM board in the 9830A, so the signals on the backplane are at TTL levels. So the memory data board (T register, as HP call it) uses TTL levels to talk to the memory.

Obviously the RAM board is going to be different between the -A and -B. The address decoder and RAM timing logic are on the memory address board, so that is likely to be different too.

[Tony Duell]

(05-26-2014 08:16 PM)MattisLind Wrote:  I tried the REWIND button. But there were nothing but a spinning sound. No motion. I think that there should be a clicking sound from the solenoids. Either there is some fault or they were just stuck.

Yes, the rewind solenoid should operate. This is controlled by a little bit of circuitry on the Motor Control PCB and shouldn't be hard to sort out. Start by checking the solenoid itself, you are going to have problems if it is open-circuit.

Look at page 84 of 'my' schematic .pdf. The solenoid drive transistor is fed from the same signal that enables the motor. So it could be a defective transistor. Or a bad connection. But not much else.

(05-26-2014 08:16 PM)MattisLind Wrote:  When I looked into the tape unit I found that the rubber on the wheels were quite worn, so I need to fix that.

The repair articles you have mention this. The 'tyre' is a standard O-ring, you can take the drive apart, remove the 'beam' with the motors on it, and replace the O-rings.

[MattisLind]

New problems

Well. The o-rings arrived in the mail and they were easily replaced. The clear leader lamp was broken so I replaced it with a white LED (yes I know it should have been a small 5V 60 mA filament lamp, but I argue that if a LED had been available in 1972 they would have used it). Then rewind started to work. The solenoids were just stuck.

I also tried the MARK command but it kept running for quite sometime until it stopped and then the machine was completely unresponsive. Weird.

When rebooting I recognized that it was failing to calculate things. For example 2+2 became 8.4444444, but 3+1 became 6.4444444. Strange. This used to work perfectly.

Just pressing a number and then execute also gave weird results.
0 reported back as 2
1 as 3
7 as 9

but 8 as 32.9444444
and 9 as 33.9444444

18 as 20
19 as 21

but

20 as 42

11 as 33
30 as 52
1000 as 3222
SQR(2) resulted in 2.22636363
and 2^2 in 41.96520965

What is going on?

However I could type in a small BASIC program like 10 DISP "HELLO WORLD" 20 GOTO 10 and it would run correctly.

It seems that it adds 2 to each digit but when the digit produced carry (8+2) then it gives a weird float.

But it cannot simply be some kind of problem in the keyboard input since it is handling line numbers OK. AUTO# also works just fine so basic integer arithmetic works OK.

Maybe it has to do with float numbers? I think that the memory subsystem is working since it can store a BASIC program and run it.

Since it actually is capable of doing a lot of things most of the microcode has to run properly.

Could there be some part of the ALU that is not working fully. As far as I understand the float format is implemented using BCD and one of the ALU PROMs together with portions of the A register and T register are involved. I think it is unlikely that the it is the T register that has failed since then I would probably have bigger trouble. But maybe the portion of the A register that handles BCD? Maybe some output stage has failed? Or the BCD ALU PROM?

It seems that I need to create some extender boards and start up my trusty old HP1664A logic analyzer.

All help highly appreciated!

[Tony Duell]

It is very unlikely that this is caused by a problem with either the A or T registers. I think that would stop the machine from working at all

An ALU problem -- the second ROM that handles the 3 higher bits of the BCD adition -- is also not very likely, but possible. Check the BCD carry flag flip-flop too, although that is also not too likely to be the problem.

Alas my first guess is a main ROM problem. Or maybe RAM -- perhaps a few locations in the system area are malfunctioning.

[MattisLind]

This problem kept me thinking and looking in the schematics.

I wasn't at all sure that it was a RAM or ROM problem since when I set it to FLOAT11 precision and entered 1000000 it responded 3.22222222222+E6. It was handling the exponent all right but the mantissa was wrong in each digit. The fact that it actually added two to each digit (22222 became 44444) turned my eyes to the ALU ROMs.

I checked the BCD ROM but it was exactly as the dump provided by Tony. One funny thing was that the machine could run BASIC programs without it! Although calculations gave even stranger results.

Then I checked the main ALU ROM. The first 128 nibbles read all right. But the last 128 nibbles were the inclusive OR of the corresponding nibble in the first half! Checking the schematics shows that the upper half is addressed by the BCD flag. So it makes sense that BCD arithmetics isn't working but all normal arithmetic works fine!

I ordered a replacement PROM from Bulgaria, programming of the chip was included in the price! Although I think it should work with the Data IO 29B I have here, I have had some difficulties in the past with some Harris chips that it were not able to program and I never tested to program a Signetics chip in it.

Hopefully this solves the problem.

[Tony Duell]

I am (slightly) surprised, ALU problems normally stop these machines from working at all, but I guess BCD operations are only used for expression evaluation on the 9830

Yes, input A7 to the first ALU ROM is signal X2 on my schematic. X2 is the active-high version of output 2 of the decoder for the microcode word X field, it is asserted for BCD operations. You were, I guess, lucky. If anything else had failed in this ROM, nothing would have worked.

Let's hope that's the only problem.

[MattisLind]

Running again

The programmed 82S126 chip arrived from Bulgaria today. Nikolay had done a good job programming it. I checked it in my DATA I/O and it verified OK.
Soldering into place on the boards and my HP9830B was back to life again! It was now able to calculate things.

Now I was able to continue where I stopped when it all started to fail; getting the tape drive to work. Unfortunately it wasn't working very well.
The MARK command still made it spin for ever and when it eventually stopped the machine was completely hung. A power cycle was needed to recover.

With most of the tape on the right spool REWIND only made it rewind for short moments until it stopped again. It might be that the friction between tape and head is to high. This type of problem has happened when I was repairing a DEC TU60 which is very similar.

Doing all sorts of other tape commands, like TLIST, STORE, FIND etc gave a ERROR 58 which seems to be some kind of general fault. And this happens immediately. It is not even trying to do something.
There has to be something weird with the tape unit itself or the controller logic. Need more investigation!
I am a little bit confused by fact that the MARK command executes but never stops. What is the machine waiting for to happen? Since REWIND is working I think that the EOT/BOT LDR detector is working.

[Tony Duell]

When you press the rewind key, what exactly happens? What should happen is the solenoid should engage, the motor start and the tape rewind until the optical BOT sensor detects the leader.

If the motor runs for as long as the key is held down and stops when you release it, then this generally means a sensor problem. Check the BOT sensor signal (there is an error in my schematic, there should be no feedback resistor on the op-amp, rather a resistor from the -ve input to ground (IIRC)) and the microswitches that detect the cassette and write-enable tab.

Or do you mean that the motor runs and keeps running, but the tape stutters along? That's a mechanical problem. Maybe a bad cassette. Or too much friction in the drive system somewhere. It shouldn't be too hard to find. You imply the tape moves normally during the MARK command, this suggests there is no problem with friction on the head.

As for what the MARK command is waiting for, of course it does writes to the tape, so it's waiting (at least it should be) for a 'next byte' request from the controller. Once you've got it rewinding properly, then check the write clock is running, ditto the bit counter, and so on.

[MattisLind]

What happens when pressing the REWIND key:

That depends. If is reasonably near end of tape (up to maybe one third into tape) it will rewind to clear leader without me holding down the button. So EOT/BOT detect works. But it happens when further into the tape that I need to keep it pressed or when I press it moves maybe 10 seconds then stops. It sure looks like some kind of mechanical problem. When it stopped like this, before it reached BOT, and then I just ejected and reinserted the cassette it would turn another 10 seconds when pressing the REWIND button. Without this manoeuvre it would stop immediately.

Yes it runs when executing the MARK command. And it runs for almost the entire length of the tape which was not what I anticipated. Then suddenly it stops and the machine is hung. Pressing STOP doesn't help. This could be a missing write clock. I'll check that.

Is there some circuitry which stop movement if the torque needed is to high?

I will test with other cassettes but this type of data cassette with blank leader is quite tricky to get hold of. I am not sure that the leader of a standard audio cassette would be detected. A few old cassettes had a problem in the DEC TU60 where the friction against the head and felt pad was to high. Apparently this is a common problem that the oil on the tape evaporates over the years which then would increase friction.

The issue that a eject / insert cycle makes a difference is puzzling to me. I simply cannot understand what kind of difference that makes.

So: Yes. There could be a mechanical problem in the drive. Or the torque applied by the motors is to low. Or the cassette is not very good (although these works in a TU60). But the BOT/EOT detector is ok.

It has to be some kind of fundamental problem that gives an immediate ERROR 58 to all other tape operations. So I think that there are some logical problem as well. I'll check those small micro switches to see if those are all right.

[Tony Duell]

This is strange....

Let's look at the manual rewind circuit (all references from my schematics). Pressing the rewind key sets U4a on the tape controller PCB (09865-66562). This then turns on the motor, selects reverse direction and high speed via U6a-c.

U4a can be cleared in several ways. One is by a tape command ending (rising edge of runcmd/). It's worth checking this signal isn't toggling.

Of course U5d clears it too. This together with U16b, etc, means a rewind ends when there is a power-on reset, when the cassette is removed, at the end of a seek-for-mark (stoptape/ asserted) or when speedclamp is asserted. The last comes from the BOT/EOT sensor via circuitry on the tape interface PCB.

The fact that removing and reinserting the cassette makes a difference is curious too. This of course will operate the microswitches. It also resets the EOT circuit on the tape interface PCB (U6b).

So, what I would do. Put a logic probe on the 3 signals going to U16b (tape controller PCB) and the output of U16a. Find out just what is ending the rewind.

There is, AFAIK, no overtorque circuit (i.e. nothing that monitors the motor current). I think you can ignore that. The only possibility in that area is that one of the power supply rails is being pulled down, which would cause all sorts of problems. Worth checking, but I think it's unlikely.

At this stage I would be investigtinh those microswitches (which can cause odd faults) and the BOT/EOT sensor (ditto).

[MattisLind]

BOT sensor

Well. I thought replacing the filament lamp with a LED was working all right. It turned out that it probably was to bright. It made that EOT/BOT LDR to make false positives.

I recognized this as when it did stop in the middle of the tape when rewinding and I pressed (and held down) the rewind button it just rewound very slowly (exactly as it did when on leader). Then when ejecting the cassette and replacing it again it started to rewind just fine for a while. I guess that the tape was slightly differently positioned with this maneuver.

Anyway. What I did was to increase the resistor value.

So, Tony, you were spot on!

Now it can rewind the entire cassette many times in a row without stopping in the middle.

But still the MARK commands goes on for ever (until blank leader at EOT) and then the machine is completely hung. The other tape commands just give a ERROR 58.

I am about to get some extender card to actually be able to attach the logic analyzer probes. Those different connector size are pretty annoying... six or seven different extender cards are needed to cover the entire machine.

BTW. The write protect and door switches are actually working, at least when pressing them manually.