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gridrunner 23rd Jul 2022 1:46 pm

HP 150 Touchscreen II repair
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Hi everyone,

I've just got hold of a HP Touchscreen 150 II computer (without the touch screen option) and it has a fault. I haven't turned my attention to the floppy drive unit or the fixed disk unit, but I'll document my travels with this as I go.

The first issue is the screen is dead. The chassis mount fuse is intact but there's no CRT heater I can see so I suspect a PSU issue. However, I can't fathom a way in to the plastic case. There seems to be a hidden set of tabs that are holding the case in and I don't want to force it. I have the service and user manuals, but they don't show disassembly.

If anyone can offer advice on how to get in, I'd appreciate that first :)

I know Tony is the group and is credited with providing schematics for the machines. Tony, any thoughts :)

many thanks!

gridrunner 23rd Jul 2022 4:28 pm

Re: HP 150 Touchscreen II repair
Just a quick update on this. I've found me way in, applying power there is a CRT heater and the machine powers on, but the diagnostic LEDs are all lit and there's no display.

gridrunner 23rd Jul 2022 7:28 pm

Re: HP 150 Touchscreen II repair
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Quick update number 3 on this, the machine's diagnostic leds are fully lit and it won't run diagnostics or boot. If I remove the co-pro board, the machine does then go through it's diagnostics process and I get a beep. However there's no HT to the monitor. I did get heaters, but there's no fizz or static to the screen so something's down in the monitor circuit on what I guess passes for HP's analog board.

TonyDuell 24th Jul 2022 6:54 am

Re: HP 150 Touchscreen II repair
I'll have a dig around for you. I certainly have the technical manual with the circuit diagram of the motherboard and I may well have some information on the PSU/monitor PCB.

From what I remember the monitor section is fairly conventional though.

gridrunner 24th Jul 2022 8:00 am

Re: HP 150 Touchscreen II repair
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Many thanks Tony, the schematic for the PSU and Monitor section would be very useful. The computer voltages test fine, there is a heater voltage for the tube but no sign of any high voltage for the anode. The board looks clean without any obvious failure points, apart from the usual battery problems on machines like this.

TonyDuell 24th Jul 2022 8:44 am

Re: HP 150 Touchscreen II repair
There's no official schematic, I do have the reverse-engineered one of the board in my 150-II but it is very possible that there were several manufactuers of said board. My HP150-II is a very early one, so early that the 'Elmer' ASIC is actually a daughterboard full of standard ICs fitted alongside the coprocessor board.

Let's see how close our two boards are before going much futher.. The monitor-related ICs on mine are :

Vertical deflection : IC31 AN5763
Horizontal centring/delay : IC42 AN5791
Horizontal osicllator : IC41 AN5753

If those agree it's worth me suggesting testpoints etc

gridrunner 24th Jul 2022 8:53 am

Re: HP 150 Touchscreen II repair
Hi Tony,

thanks for that. Those ICs match what I'm seeing on the board. I've got chassis number Y44 on the silkscreen.

TonyDuell 24th Jul 2022 9:05 am

Re: HP 150 Touchscreen II repair
I suspect it is the same board then. It'll take me some time to get round to scanning the diagram though

The monitor section is quite conventional. The CRT voltages come from the flyback transformer (line output transformer). The monitor is powered from the 12V output of the power supply, the CRT heater is run straight off that. Since the heater is glowing, the 12V rail is present, my guess is an issue in the horizontal side.

Start with the CRT pin voltages, what do you measure on pins 5 (control grid), 6 (first anode) and 7 (focus anode). Be careful, the last 2 should be a few hundred volts (all are less than 1kV). If they're all missing, sounds like a line output stage fault.

Line drive comes from pin 7 of IC41. This directly drives the driver transformer L430. Secodary of that goes to base and emitter of Q44, the line output transistor. Although the collector of same is tied to the 12V rail, this is not an emitter follower, due to the drive being connected base-emitter it's a common emitter amplifier as normal. T401 is obviously the line output transformer.

So, check line drive, check Q44, doing a ringing test of T401 I guess.

gridrunner 24th Jul 2022 9:35 am

Re: HP 150 Touchscreen II repair
Thanks for the help Tony, I'll check those voltages. Is it OK to test the board outside the machine, or should I refit it to the computer and CRT?

TonyDuell 24th Jul 2022 9:54 am

Re: HP 150 Touchscreen II repair
It should be OK to test it on its own, I don't think the power supply needs a dummy load to work. But do check the power supply output voltages just to be sure they are coming up and not going to invalidate all the other tests.

There's a 20 pin connector to the motherboard, the pinout is :

1 FullBright video
2 ground
3 HBright video
4 Hsync
5 Vsync
6 N/C
7 Power On
8 VBat
9 +12V
10-15 ground
16-19 +5V
20 -12V

Do you have a 12V bench supply? If so, unplug the red jumper wire at pin B2 (it's soldered to point B1) and connect said supply between ground (-ve) and the pin at B2 you just unplugged the wire from). That's the 12V feed to the monitor. Doing that will avoid any problems from the SMPSU not having a load, and will also mean there's not mains on the board you are working on (there should be other high voltages of course)

gridrunner 24th Jul 2022 10:04 am

Re: HP 150 Touchscreen II repair
Thanks Tony that’s a great tip. I do have a bench PSU so I’ll do what you suggest this evening and report back.

gridrunner 24th Jul 2022 11:30 am

Re: HP 150 Touchscreen II repair
Hi Tony,

I've applied power to B2 as suggested at the neckboard I'm seeing the following:

1 - 0.018
2 - 41V
3 - 12v
4 - 0.012
5 - -40V
6 - 484V
7 - 199V

TonyDuell 24th Jul 2022 12:00 pm

Re: HP 150 Touchscreen II repair
Well, the line output stage is certainly running. Are you sure there's no EHT?

I'd reconnect the jumper at B2, then put the board back in the machine. Power up and check those voltages again, in case the CRT is shorting internally or something.

After that, I'd suspect a fault on the logic board, the video monitor is actually working but not being given anything to display.

gridrunner 24th Jul 2022 12:11 pm

Re: HP 150 Touchscreen II repair
Hi Tony, I will do. Maybe it's a bad assumption on my part. The machine was working previously although it had an error code 1000 displayed (I believe this is to do with a touchscreen option, but this monitor doesn't have that option).

The screen currently has no display but I a had hunch something was wrong with the HT because I can't hear or feel any static build up or 'fut' that you usually get with CRTs, but then I suppose this is quite a small tube.

The other strange thing was that the machine had the co-pro option fitted. When I powered the machine on, all the diagnostic LEDs were lit and stayed lit.

Removing it allowed the LEDs to cycle through the boot process and they all go out, but the display is still blank. The 5V rail is OK if a tad low at 4.98V. It doesn't drop with either the co-pro board or the extra memory board attached.

TonyDuell 24th Jul 2022 12:44 pm

Re: HP 150 Touchscreen II repair
This is very odd...

The 8088 on the motherboard is strapped so the pinout is 'minimum'. Like that it can't support a coprocessor. So the Coprocessor card, as well as containing the 8087 contains second 8088 strapped in 'maximum' mode and some interface logic. When you fit the coprocessor card it disables most of the signals from the motheboard 8088 but you have to cut jumper W1 on the motherboard to disconnect the ALE line coming from the motherboard processor. And if you later remove the coprocessor you have to re-jumper W1.

Is this machine known to have worked with the coprocessor fitted?

I know they are very hard to get to, but is the motherboard outputting anything on the Hsync, Vsync and the 2 video pins? Aha, there are some video test points on the motherboard located between the row of LEDs and the beeper. According to the manual they are :

TP8 NFB Actve low full bright video
TP7 SGnd Ground
TP6 CSYNC Composite Sync
TP5 NHB Active low half bright video

Note that according to the schematics, CSYNC is generated along with the hsync and vsync signals by one of the ASICs. I guess it would be possible for it to work and one of the latter 2 signals to have failed. But unlikely

gridrunner 24th Jul 2022 7:43 pm

Re: HP 150 Touchscreen II repair
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Thanks Tony, well some progress. I reflowed some solder joints for the power connector and the LOPT, as well as some joints that looked a little suspect. When I reconnected the board I could see a display. it's maybe a little dim and needs some adjustment, but it's progress.

The strangeness with the co-pro board remains. The machine had the option already installed and it was working with it. Now it seems to have spontaneously failed, which seems a little dubious. I'm not sure if a motherboard jumper has been broken as the machine boots without the card and any adjustment to the motherboard, but when the card is installed - all the LEDs light and it won't produce a display. Maybe this was the fault the previous owner was referring to, as there's no display with the card installed.

gridrunner 24th Jul 2022 8:21 pm

Re: HP 150 Touchscreen II repair
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Another quick update on this and some more success. I'm able to get a display with the co-pro fitted and the memory board. I re-flowed the solder joints to the connector for the co-pro board. I'm not sure if that did it, or just wiggling, but there are clearly connector related gremlins affecting the machine.

About the 1000 error Tony, there is mention of this relating to the touchscreen, could it be that with the battery failure, the machine is forgetting that it doesn't have the option?

About the touchscreen, if I ever wanted to find one (I'd like to) is that a kit to fit or a whole new unit? There is a ribbon cable present for the touch sensor that disappears inside the bezel.

Now, there are two other units to tackle:

TonyDuell 25th Jul 2022 3:42 am

Re: HP 150 Touchscreen II repair
The W1 jumper I mentione is a wire link (probably a 0 ohm resistor) alongside the 8088 CPU on the motherboard. It should be easy to see if it's cut. My guess s that it is not, the machine can't work without the copro board if it is.

I'll have to find the service manual (as opposed to the technical manual) to look up the error codes. The touchscreen is an HP-HIL device. the same interface is used for the keyboard. Does the keyboard work? If not, get worried, the HP-HIL system uses an HP custom interface chip and a programmed 8042 microcontroller.

The touchscreen upgrade consists of a new bezel containing the touchscreen electronics. As you probably know it was an array of IR LEDs and sensors, by detecting which beams were broken it worked out where your finger was. It plugs into a socket on the CRT mounting, that's the ribbon cable you've found. The same touchscreen fits a couple of HP video monitors too.

ScottishColin 25th Jul 2022 10:49 am

Re: HP 150 Touchscreen II repair
No help from me - just to say I remember using/replacing these in about 1990 at Colman's in Norwich which was an HP site - several HP 3000's running the site's central systems and HP hardware everwhere.

We were in the process of swapping out to HP Vectras at the time, but I fondly remember these devices, along with Thinkjets, Scanjets and Quietjets.

If I remember rightly, there was an option on the HP 150 to have a printer built into the device - I don't suppose yours has one of them?


TonyDuell 25th Jul 2022 11:02 am

Re: HP 150 Touchscreen II repair
The original HP150 (9" CRT, always has the touchscreen) can have the printer fitted in the top. The HP150-II (12" CRT, touchscreen is a somewhat uncommon option) can't

There are considerable hardware differences between the 2 versions. I have both along with the technical manuals. The older one is mostly standard ICs, I think there is one HP custom part in the graphics circuitry. The later one is stuffed with ASICs, alas.

Incidentally if anyone is restoring the oriignal version and needs the printer, I probably have at least one spare.

gridrunner 25th Jul 2022 2:51 pm

Re: HP 150 Touchscreen II repair
Hi Tony, I'd love to get hold of an original 150 to go alongside this unit. I particularly wanted to get a touch screen model, as I have a thing for this technology and how it's evolved. I have here a Samsung Surface table (which is the 2nd gen Microsoft Surface technology) where the IR sensors are embedded into the screen so it can 'see' hands and objects suspended above it. Really rather cool.

The keyboard does work, but there was a scare because the cable had been gnawed by mice and then fitted the wrong way round. A quick fiddle around got it working, but it is missing a key :(

The co-pro isn't playing ball again. I need to get the PCB out. I'll do that when I fit batteries to the power board. Where is the CPU by the way? Is it tucked away out of sight?


gridrunner 25th Jul 2022 2:53 pm

Re: HP 150 Touchscreen II repair
About printers, this one has a think jet that came with it. I was shocked and surprised to find you can still order cartridges for it almost 40 years later!
I believe the think jet was the first commercially available inkjet printer to reach the market.

TonyDuell 25th Jul 2022 3:23 pm

Re: HP 150 Touchscreen II repair
I don't think I have any complete spare 150's, sorry.

The HP touchscreen with its scanned array of IR beams was an interesting way to do it, but ultimately it was too limited in resoultion so died out. I remember Steve Ciarcia had a project based on it in his Circuit Cellar articles in Byte magazine some years before the HP150 came out, said article metions a patent owned by one of the American universities, I forget which but it might be worth tracking down.

The touchscreens are quite different electronically between the 2 machines. The HP150 one has a custom interface that links to an 8041 on one of PCBs. The HP150-II is an HP-HIL peripheral, as I mentioned it also fitted at least one HP video monitor and was used as such with some HP9000-series machines.

The HP150-II processor is roughly in the middle of the motherboard I think.

Which Thinkjet do you have? I assume either the HPIB or RS232 version, to use the HPIL or Centronics ones with a 150-II would be perverse at best. I have the full service manual for that unit too, BTW. NEVER leave the cartridge in the Thinket when you are not using it. If the cartridge leaks ink, it will drip onto the flexprint that connects the cartridge to the control PCB and corrode the traces. Replacement flexiprints are very hard to find, the easiest source is another Thinkjet where the custom processor chip has failed.This is even worse on the HP Integral, the flexiprint there is longer than the one in a normal Thinkjet.

The microcontroller in the Thinkjet is a custom 8 bit HP thing with internal firmware. It has external RAM and font ROMs, oddly these connect using the 'Saturn bus' as in the HP71B handheld computers. Very strange. And yes the Thinkjet was probalt the first commercial inket printer, the name is officially a contraction of 'THermal INKJET'.

gridrunner 25th Jul 2022 3:56 pm

Re: HP 150 Touchscreen II repair
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Hi Tony,

I can see what you mean about the ink. The cartridge was left in the unit and it has ruined the cartridge although that wasn't likely to be of much use I know :)
I have been able to clean off the residue and it looks like the Flexi might have a fighting chance. It is a HP and not centronics interface on the back.

I'll see if I can attach it if I make progress with the disk drives and hard disk.

TonyDuell 25th Jul 2022 4:03 pm

Re: HP 150 Touchscreen II repair
That's the HPIB version of the printer. The microcontroller used has an internal HPIL interface, the HPIL model simply brings that out to the rear panel via the normal transformer, etc. The RS232 and Centronics models have internal interface boards that communicate with the microcontroller over a parellel data bus.

And the HPIB model? Amazingly it the same microcontroller as the HPIL version with an HPIB-HPIL interface board. Something like an HP82169 with different firmware.

I hope I am wrong, but that flexiprint is probably corroded and will be open-circuit.

gridrunner 25th Jul 2022 7:48 pm

Re: HP 150 Touchscreen II repair
Sadly Tony, you're right. The Flexi is toast. It's a shame, if only the cartridge had been put away properly. Would the printer for the 150 I you have work on this II? It would be nice to have a period correct HP printer to display with it.

gridrunner 25th Jul 2022 9:03 pm

Re: HP 150 Touchscreen II repair
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Back to the co-pro issue. I've removed the mainboard itself to have a closer look. There is a 0 ohm resistor in W1 and it's soldered in place. Now, the machine had the co-pro option fitted as can be seen from the sticker on the back. However, why would that component be present in W1?

Flipping the board over shows some pretty uneven soldering including some partial joints on the purple and gold HP IC next to the copro socket.

Would this have every worked Tony configured like this? The chap who had this machine paid for the upgrade so that he could use the co-pro for his work. I can remove the link and try to see if it boots with the co-pro attached.

gridrunner 25th Jul 2022 9:46 pm

Re: HP 150 Touchscreen II repair
I did notice when fiddling around that it's possible to fit the co-pro board in such a way that it looks as though it's attached, but it's not in fact fully seated. This may explain why it appeared to work earlier, but not if I attach it firmly into the socket (the machine hangs with all diag LEDs lit). Could it be that this chap has had an upgrade fitted for all these years that never actually did anything?! wow..

TonyDuell 26th Jul 2022 4:02 am

Re: HP 150 Touchscreen II repair
I would try removing link W1. The techref makes it very clear you have to do so, the ALE signal will not behave properly if driven from 2 sources (the coprocessor board and the original 8088 via W1).

No idea why there's resoldering on the IC next to the coprocessor socket. That's the 'Elmer' ASIC, real time clock + baud rate generators +... Very early machines have 50 pin header in place of it, then a daughterboard fitted. Perhaps your Elmer IC was replaced at some point.

As for the printer, the one for the orignal HP150 won't work in a 150-II. There's a special interface circuit for it on the 'frontplane' (the PCB that interconnects the other boards) and a power connector for it on the PSU board. Your best bet is to find another Thinkjet with a good flexiprint (any interface version) and to swap the flexiprints or to have one made (are there companies that do that?)

gridrunner 29th Jul 2022 3:42 pm

Re: HP 150 Touchscreen II repair
Hi all,

Just a quick update on this. Removing the link to W1 is now letting the machine boot with the co-pro board installed. I can only assume that the upgrade option the previous owner had installed has never worked in over 35 years. I suppose that if you never had seen the difference between co-pro and no co-pro support, you might not be able to tell if it was functioning or not. It was apparently purchased to speed up AutoCad.

I've stripped down and cleaned the keyboard so the next stage after re-assembly is to get time to look at the hard disk unit.

TonyDuell 29th Jul 2022 3:48 pm

Re: HP 150 Touchscreen II repair
Which hard disk unit do you have? The suffix letters are very important, BTW.

gridrunner 30th Jul 2022 8:53 am

Re: HP 150 Touchscreen II repair
Hi Tony, the model number is 9133D

TonyDuell 30th Jul 2022 11:51 am

Re: HP 150 Touchscreen II repair
Looks like the controller board is much the same as the one in a 9133H which I have worked on.

What is your hard disk unit doing/not doing?

gridrunner 30th Jul 2022 1:36 pm

Re: HP 150 Touchscreen II repair
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Hi Tony,

On the dust-o-meter I'd rate this unit a 10!

I think I'll clean it up and test the PSU before trying it.
I'll keep you posted.

TonyDuell 30th Jul 2022 3:14 pm

Re: HP 150 Touchscreen II repair
With the double-head floppy drives it is_essential_to strip the disk holder and clean the hardened grease off the latch mechanism. This applies to the drive in that hard disk unit and ones in things like the 9122 dual floppy drive. If you don't, the holder doesn't latch up properly, the upper (down) head catches in the disk when you eject it and can be ripped right off the gimbal spring. I can remember roughly how to do it, if need be I'll strip a spare drive to check.

gridrunner 30th Jul 2022 7:49 pm

Re: HP 150 Touchscreen II repair
Hi Tony, this chap has a YouTube video on fixing this particular issue I think. Does it look correct?

TonyDuell 2nd Aug 2022 4:11 am

Re: HP 150 Touchscreen II repair
I don't 'do' videos for such things. I prefer to read text and see still photos.

I took a quick look at that youtube thing, as ever I got a headache after a minute or so. From what I can see it does cover the issue, but it doesn't do the way I do, which is to dismantle the drive, take the complete disk holder out, then take that apart and clean it up. Note that there are 2 versions of the disk holder, the older one is mostly assembled with E-clip and comes right apart, the later one has levers rivetted in place, there are fewer parts to remove and get mixed up but it is a lot harder to clean off the hardened grease,

If you PM me with your e-mail address I can send you something on this.

gridrunner 5th Aug 2022 6:01 pm

Re: HP 150 Touchscreen II repair
Great news Tony, the floppy drive was serviced and can read disks fine. The hard disk is also working, which is fantastic.

The clip is less than a minute.

gridrunner 5th Aug 2022 6:07 pm

Re: HP 150 Touchscreen II repair
Luckily the grease hadn’t dried up so I was able to clean up the old grease and apply some new, working it into the mechanism. I cleaned the heads with a chamois swab. The power supply has had some slight attention with a couple of capacitor changes. The only question is how to make the hard drive which seems to be drive B bootable. I’m booting off a floppy disk on A. Do you happen to know if the floppy disks are readable in a x86 MS DOS machine?

TonyDuell 6th Aug 2022 3:46 am

Re: HP 150 Touchscreen II repair
The HP150 _is_ an 'x86 MS-DOS' machine and is clearly able to read its own disks. So I assume you mean a PC-compatible machine here.

Normal PC hardware (although not those USB-interfaced floppy drives) is capable of reading/writing the HP150 disks But the format is different and the normal PC MS-DOS won't read them as standard. Back in the day there were various utilities, freeware, shareware, etc to read/transfer files. No idea where to find them now.

gridrunner 7th Oct 2022 4:23 pm

Re: HP 150 Touchscreen II repair
3 Attachment(s)
Hi everyone,

So, these HP 150s are now multiplying!

I recently picked up a HP 150 model 1, with the touchscreen and a printer, keyboard and a disk unit the HP9122.

The printer, like the previous unit is toast because the ink cart was left in.
The previous owner said the machine was working when put away but it now no longer comes on.

I've stripped the machine down and discerned a problem right way. Damned batteries. The pair of LR1 cells for the cmos backup had corroded and leaked onto the video PCA board. In a very bizarre way the green goblin had furred the majority of the exposed PCB joints and IC legs on most of the component side and had even managed to reach the connector at the far end of the board! That said, it hadn't done any NICAD level of damage, so there's no discernible damage to traces.

I've cleaned it off and paid special attention to the connector to the backplane.
I've replaced some out of spec and leaking capacitors on the power board and carefully cleaned the touch screen photocells.

The power supply is healthy, but on power on there is no display and no start up beep.

I referred to the service manual and decoded the LED self test codes as:

D5AA - video chip 5 error
D8FF video chip 0 error

I suspect the corrosion to the video board has done some damage. Any thoughts would be appreciated!


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