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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
1 Attachment(s)
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.

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