Non Functioning HP-150 Looking For Power Supply Schematic

[week3]

Hello,

Background and Initial Question:

I bought a non functioning HP-150 off facebook market place. I'm going through the process of trying to get it running again but i'm struggling to find the schematic for the computers power supply.


Bitsavers has its technical reference manual which seems to have every other schematic but the power supply for some reason.


The document does reference some other documents. Which I think I need the "HP150 Service Manual" "45611A" "45611-90002". But ive been struggling to find that document unfortunately. I don't know if any of yall know where it could be found?


What I know is wrong with it at the moment:
1. The main externally accessible mains fuse is blown. Looks like it had some energy behind it.

2. The main power board has a component with a chunk missing out of it. I assume its a NTC inrush limiting thermistor. Don't let the photo angle fool you it only has 2 legs. It has another of the same part next to it both are labeled TH100, TH101. The components are next to a transformer, 4 diodes, and I traced one legs of the blown one to go to the biggest capacitors on the board. Unfortunately I found the blown chunk at the very bottom of the PC so it would have had a chance to short every single logic board on its way down if I'm unlucky. There are no markings on the component itself for some reason.....

Either way based on my reading of these components if I have identified it correctly im wondering if what happened was the computer was turned off and back on fairly quickly. The NTC might have been pre heated meaning it wouldn't have blocked the inrush on the big old caps. Causing even more heating in the thermistor cracking it while also blowing the fuse. Although this could also be caused by any number of component failing causing a short.

There is another fuse on the power PCB that isn't blown. It looks downstream. But at the moment I havn't traced out what it controls. Praying one of yall has a schematic so I don't have to .

Nothing else on the board seems to have visible damage but I havn't checked any components yet.

3. Otherwise I didn't see any visible damage on other components other then the main board and the daughter board attached to it mounted poorly.


Next steps:
1. Trying to find the power supply schematic so I can figure out a replacement for the damaged TH100.
2. Replacing the external fuse.
3. Ohming out power rails looking for any shorts that could explain the power supply damage better then the powercycle theory I had about the NTC thermistors. If I don't find anything I might try to power it on again.

Overall any of yall got any advice on the direction im going or happen to know where to find the schematic or what a equivilent NTC might be?

Thankyou for your time in payment enjoy this picture of the magic behind a 1983 touchscreen crt:


Oh and if anyone needs rom dumps of this machine there are plenty I can try and dump!

 

[week3]

I hit post too soon because I found the HP Computer Museum website has some great documentation on it.
Although there still isn't a official schematic for the power supply weirdly? Just a hand drawn schematic labeled "SchematicsByTonyDuell".
God bless you Tony. Through some rudimentary research it seems like the guy does alot of reverse engineering of HP computers.

Still don't know a Part number for the thermistors but it confirms my wiring theory

 

[SomeGuy]

There is a good chance you have blown (shorted) rectifier diodes. Had something similar happen to a totally different power supply recently.

Edit: looking closer at that schematic, I see your thermistors are AFTER your rectifier, where mine were before. So could be something else going on there.

 

[Martin Hepperle]

Your ROMs seem to be version "J" and they should match the images archived at
https://groups.io/g/VintHPcom/files/HP 150 and Touchscreen II

You might also want to inspect the video board for battery leakage. This is a very common problem with the HP 150.

 

[week3]

Your ROMs seem to be version "J" and they should match the images archived at
https://groups.io/g/VintHPcom/files/HP 150 and Touchscreen II

You might also want to inspect the video board for battery leakage. This is a very common problem with the HP 150.

Ah yah those look like my roms. That site also looks like an amazing resource. Thankyou!

I'm having a hard time finding batteries on the video board based on the photos I took while I was disassembling the PC. But Ill take a better look/order replacements when I get off work.
If you do know where it is located on the board could you point it out?


Thankyou again for the help

 

[week3]

Oh nevermind the external battery pack mounts here I see. Yah the terminals were corroded and need cleaning. Luckily it doesn't look like anything leaked on the PCB though.

 

[week3]

There is a good chance you have blown (shorted) rectifier diodes. Had something similar happen to a totally different power supply recently.

Edit: looking closer at that schematic, I see your thermistors are AFTER your rectifier, where mine were before. So could be something else going on there.

C105 right after the rectifier turned out to be the issue. I don't think it was fully shorted at first but it definitely became fully shorted. I replaced C104 alongside it while I was in there.

Ordered the wrong NTCs on digikey which added a lot of waiting time. My fault for not checking the lead diameter of the ones I was replacing....

But it is at least displaying now and taking keyboard inputs! Gonna study up on how to actually operate this thing to see what else is wrong with it. But pumped I got it running. Gonna also update the nice old man I bought it from. He will be happy to hear that it is running again. Apparently the local hospital bought it for him back in the day to work on all their medical equipment.

Most likely will be bothering this thread soon with behavior questions. Thank yall for the help!

View attachment PXL_20251118_012619312.RAW-01.COVER(1).jpg

 

[week3]

Background
OK I initially ignored the power on test error but looking into them it looks like I got more work cut out for me. Going to delay working on the HDD/Floppy situation to get DOS running.
The computer responds to keyboard inputs and is able to print what I type on the printer. But the touch screen does not appear to be working.

Initially I got:

Power-on test failed 1600
Press RETURN to clear

Which according to the service manual is a hex error code found in this graph.
0x1600 = 0001 0110 0000 0000


So there are three issues:
1. Keyboard or touch screen
2. Interrupt controller
3. Video controller

Number 1 makes sense because the touch screen wasn't working. So I just took apart the computer again and gently emptied a bottle of compressed air at the touch screen sensor holes. After buttoning up the whole device the keyboard/touchscreen error went away instead displaying:
Power-on test failed 0600
Press RETURN to clear

Meaning only errors 2/3 remain (Interrupt Controller/Video Controller)
Video confuses me because I have yet to run into anything displaying incorrectly.
Then for interrupts Ive had some instances where it seems like my keys are less likely to register. But most of the time they always do.

Looking into the interrupt controller it looks like the control uses a 8259 interrupt controller. According to the Technical Manual this is the priority list of the Interrupts
Highest
IRO Video
IR1 Datacomm (7201 and front plane interrupts)
IR2 +5V (Video second level tasks)
IR3 Keyboard and Touch Screen
IR4 Front plane interrupts (lower level)
IR5 HP-IB
IR6 (not used)

IR7 Real-Time Clock
Lowest

Which the terms used seem to line up with the listed pin out of the interrupt IC so im assuming they are referring to physical pins


I'm starting to wonder if Ill need to scope onto the interrupt pins and see if any of them are acting funky (not looking forward to figuring out how to scope on this compact little machine). Also wondering if whatever is causing the video test to fail is also generating a bunch of bad video interrupts that is failing the interrupt test. Need to do a bunch more reading.

My question:
Do any of yall know what the control is doing during the "Video Controller Test" or the "Interrupt Controller Test"? I feel like if I had a stronger idea of how the test is being conducted I might be able to pinpoint what I need to scope onto faster.


Thankyall again for all the help!
Don

 

[Thatsmanjear]

C105 right after the rectifier turned out to be the issue. I don't think it was fully shorted at first but it definitely became fully shorted. I replaced C104 alongside it while I was in there.

Hi, I recently acquired an HP 150 that blows the external fuse immediately upon turning on the power. I took it apart, suspecting the power supply, and found I had a broken component, did some googling, and looks like you had the EXACT same issue, a broken thermistor. I too had found the utterly amazing Tony Duell handwritten schematics. I replaced the fuse and powered mine on again to see if I could use my thermal camera to quickly capture where a short might be, but didn't need a thermal camera, the spark and bang made it obvious. It is the intact left thermistor in my picture, and it is arcing between the right outside prong with the right side of the disk. Those two points aren't touching, but have about 1mm clearance.

Did you replace your thermistor, or did you just replace the C104 and C105 caps? I'm assuming my arcing issue is because something upstream of the thermistor is bad? As opposed to the thermistor itself? I'm more of a software guy, so sorry if I'm asking easy questions!

 

[week3]

I replaced both the thermistors and rectifying caps.

I am now realizing I wrote the wrong capacitors in my post. Apologies. I'm going to edit them so its correct. I meant to call out C111 and C112. You probably wouldn't see them get hot with your thermal camera as they are located in the metal box. They are big old electrolytic capacitors and could very likely be leaking and shorted. Id run a multi meter on the bottom side of the circuit board and just check to see what the resistance across the two leads of each capacitor are. Mine showed 0.3 ohms indicating the capacitor was toast. While you are there check the diodes as well D105,D102,D104,D103.

Warning: Since you said you were more of a software guy not a hardware guy these are big capacitors that are rectifying line voltage. Pretty dangerous voltages can be present long after you turn off the device. Some safety advice in case you don't know(and apologies if you do):
1. Make sure the device has been unplugged for a little bit before messing with it.
2. If you are messing with high voltages make sure to work with one hand and make sure you are not touching metal with your second hand. You don't want a short across your heart.
3. Discharge all capacitors before handling the device. Technically you should use a settup with a resistance so it discharges slowly instead of sparking. I get lazy and use a electrically insulated screwdriver when im pretty sure its allready discharged anyways.



While only one of my thermistors was bad I replaced both of them. I couldn't find an exact match replacement part wise so I wanted to make sure both lines responded to inrushes in the same way.
This is the part I used.
Warning: It should really be rated for 3A instead of 2.9A since the fuse before it is 3A. But at the time it was hard to find a proper thermistor that was rated higher that still had the proper lead sizes for the holes. The lead sizes on this one will work. If you can find a part with similar characteristics but rated >=3A steady state then you would be golden. For me... 2.9A was close enough...

What reallllyyyyy has me curious is the fact that you are seeing arcing at all on the intact thermistor. From my memory those metal bars to the side of the thermistor are just used to keep the thermistor in place in transit since this is a "portable device". I thought that the metal bars were connected to the same net as the thermistor lead they were closest to. So hypothetically I thought that they should be the same voltage and it would be impossible to arc. But ill check when I can access my device again. Overall im gonna think on what could cause that.

Some various other advice while im rambling. If you are power testing the supply board id make sure it has loads hooked up to the outputs that meet atleast the minimum loading requirements so the outputs don't go crazy.

Also Im jealous of the thermal gun settup. If you really want to spice up that type of debugging get a variac to slowly increase the input voltage to the board so that it fails slower and the hot spots are more obvious. If you arn't doing that allready.

 

[Thatsmanjear]

Wow, thanks for such a thorough response.

Id run a multi meter on the bottom side of the circuit board and just check to see what the resistance across the two leads of each capacitor are

I used my LCR meter to measure them both. One measured 628uF with .03 ohms ESR, the other 600uF, .03 ohms ESR. The four diodes all tested good.

Warning:

Thank you for all those. I'm always diligent when working on CRTs, but admittedly aren't careful when working on smaller power supplies. Now...the old IBM power supplies with caps the size of soda cans, another story, lol!

This is the part I used.

Thanks for that link!!

From my memory those metal bars to the side of the thermistor are just used to keep the thermistor in place...

Hmm, you're right. I just checked, the side of the thermistor and bar are indeed on same trace, I just did continuity meter just to make sure, yep. That is weird. I wonder if the arcing I saw was between the opposite leads under the disk, and in the quick flash where it happens I didn't catch exactly. Could that happen because I didn't have any load on any of the rails (see below)?

If you are power testing the supply board id make sure it has loads hooked up to the outputs

OK, I didn't have anything hooked up for a load. I have a little makeshift load generator using car headlight bulbs in series. Do you think I need to have all rails loaded simultaneously?

By the way, you got a great bundle, I'm jealous. I'm lacking a keyboard, and those seem to be unobtanium... I thought I could get one of my many HP terminal keyboards that have RJ11 jacks to work, but from what I'm reading they aren't compatible.

Thanks again.

 

[Thatsmanjear]

I was wrong about the location of the "arc". I think the thermistor itself is shorting. I recruited my wife to video from a different angle, so that between the two of us we could capture exactly where it's happening. It's the broken thermistor. For your viewing enjoyment! Lol.

Angle1.mp4

drive.google.com

Angle2.MOV

drive.google.com

 

[week3]

Oh jeez its really going in that video. Yah id replace those thermistors just buy a couple of extra in case you blow more in the debugging process.

Hmm, you're right. I just checked, the side of the thermistor and bar are indeed on same trace, I just did continuity meter just to make sure, yep. That is weird. I wonder if the arcing I saw was between the opposite leads under the disk, and in the quick flash where it happens I didn't catch exactly. Could that happen because I didn't have any load on any of the rails (see below)?

I don't *think* so but it wouldn't hurt. My gut would guess there is a shorted electrolytic somewhere.

Also while on the subject. Have you located the part of the thermistor that was turned into a projectile? Its conductive and could short things out.

OK, I didn't have anything hooked up for a load. I have a little makeshift load generator using car headlight bulbs in series. Do you think I need to have all rails loaded simultaneously?

Tbh these old power supply's are one of my weaker subjects. I would provide a load for the +12V rail, -12V rail and +5V rail. Id be worried about each building up too much of a charge unloaded on the secondary of that transformer. But also I can't fully explain my reasoning so take it with a grain of salt.

In my case I got a bit lazy and just used the computer as the load because the fuse had blown while everything was hooked up originally. Thinking if the supply nuked the computer it would have already happened. The service manual and schematic also imply a level of overvoltage/overcurrent protection. IDK how much id recommend relying on it but I choose to and I wouldn't reccomend doing many quick on off cycles.

By the way, you got a great bundle, I'm jealous. I'm lacking a keyboard, and those seem to be unobtanium... I thought I could get one of my many HP terminal keyboards that have RJ11 jacks to work, but from what I'm reading they aren't compatible.

Yah the guy I got it from was super sweet and was happy to see someone repair it. I havn't looked into the keyboard/protocols but if there isn't documentation on it online and you are thinking about making an adapter I could log communications for you.

 

[Thatsmanjear]

My gut would guess there is a shorted electrolytic somewhere.

I'll measure them all today, but probably just go ahead and order/replace the two big caps since I have to pay for digikey/mouser shipping anyway for the thermistors.

Have you located the part of the thermistor that was turned into a projectile?

Lol. When I first got the unit I heard something rattling around, so I shook it out and saved it in a baggie before I knew what it was.