IBM Rev A 5150 dead - assistance needed!

[tspope]

Hello. I am longtime computer tech head and recently came into a mostly original very early model rev A 5150 (s/n below 105000) with the 16-64kb board I am trying to return to original. It did not have original SS 5.25 FD drive and it had an updated U33 BIOS chip which I managed to bend/break the pins pulling out (embarassing) when attempting to figure out why I wasn't seemingly getting power which brought me here.

I stripped it down to the minimal config -- original 1981 PSU with the raised nuts (fan spinning), motherboard and speaker but not getting any beeps. I tested the voltages with the P8 and P9 plugged in to the motherboard and everything matching the -0 degrees website working range. +5v +5 +5 -5 +12 -12

Id like to get something on screen but only have a 5151 monitor which will not work with the original CGA card -- first question is what kind of screen could I hook up to the RCA output? Unit has a 1501985 Black and White Parallel card -- what simple type of display will work on this? 5151?

Second question is now that I broke the bios chip and I most likely will not find the original 5700051 anytime soon, where can I get a replica/programmed chip replica replacement? Is it recommended to buy the Landmark Diagnostic chip?

Then to figure out how to get the minimal configuration to give me a sign of life or beeps. I am following the dead 5150 walk through on -0 degrees but not sure how to get measurements on the memory bank blue tantalums as the legs are almost inaccessible to my voltage tester.

There is a chip labeled C8087-2 populated in the space next to the 8088 '78 chip.

Could the settings of SW1 or SW2 have have something to do with this?

Any ideas much appreciated.

 

[modem7]

I tested the voltages with the P8 and P9 plugged in to the motherboard and everything matching the -0 degrees website working range. +5v +5 +5 -5 +12 -12

That is a good start.

The power supply, being an early one, may power its fan via AC, rather than by 12V DC. If so, there is something that you need to keep in mind. If, whilst you are diagnosing/repairing things, a tantalum capacitor (or something else) goes short-circuit, overloading the power supply, you will still see the fan turning. That could mislead you into thinking that the power supply is functioning, producing output voltages

Thinks are different for the power supplies that power their fan via 12V DC.

first question is what kind of screen could I hook up to the RCA output?

I have an old LCD based TV that can display that composite video . See [here].

Unit has a 1501985 Black and White Parallel card -- what simple type of display will work on this? 5151?

That card is the 'IBM Monochrome Display and Printer Adapter', commonly referred to as the IBM MDA card.
The IBM 5151 monitor is the monitor that IBM supplied with the card.

Second question is now that I broke the bios chip and I most likely will not find the original 5700051 anytime soon, where can I get a replica/programmed chip replica replacement?

Various replacement/substitution options are at [here], some of which require an adapter.

The people/companies at [here] should be able to provide a suitable EPROM/EEPROM replacement, programmed with the 04/24/81 (5700051) code. However, note that the reason you found the 10/27/82 revision BIOS chip fitted, is because that is required to support the MFM controller and drive. The code for a replacement can be found at [here].

 

[modem7]

Continuing ...

Is it recommended to buy the Landmark Diagnostic chip?

Whether the Supersoft/Landmark Diagnostic ROM (SLDR) or Ruud's Diagnostic ROM (RDR), the chip type has to be suitable for the 5150 motherboard. So, that is a chip that can go directly into the U33 socket, or go into the socket via adapter.

Of the two, RDR is the better one for the IBM 5150. RDR is particularly good at identifying bad RAM chips.

Note that there are two versions of the SLDR - one for PC's and XT's, and one for AT's.

Yes, a suitable diagnostic ROM is a good thing to have (for now and later).

Then to figure out how to get the minimal configuration to give me a sign of life or beeps. I am following the dead 5150 walk through on -0 degrees but not sure how to get measurements on the memory bank blue tantalums as the legs are almost inaccessible to my voltage tester.

If the motherboard (or other) had a short-circuit tantalum capacitor, the 5150's power supply would be overloaded, shut-down, not producing output voltages. You have output voltages.

So, you must be doing DC voltage measurements at/near the RAM chips. You can do those measurements on certain pins of the RAM chips. A diagram showing which pins of the 4116 RAM chip are the voltage pins is at [here].

There is a chip labeled C8087-2 populated in the space next to the 8088 '78 chip.

That is the optional 8087 math co-processor chip. You can read about it at [here]. It is not needed for the computer to start/boot. If it is faulty in a particular way, it can stop the computer from starting/booting, so remove it (for now).

Could the settings of SW1 or SW2 have have something to do with this?

In every case of 'wrong SW1/SW2 settings' that I have encountered, something was display on-screen.

 

[modem7]

... and it had an updated U33 BIOS chip which I managed to bend/break the pins pulling out (embarassing) when attempting to figure out why I wasn't seemingly getting power which brought me here.

I tested the voltages with the P8 and P9 plugged in to the motherboard and everything matching the -0 degrees website working range. +5v +5 +5 -5 +12 -12

It is possible that when you plug in the replacement ROM, that all will work.

( Unless you go for the early BIOS revision, it which case the MFM controller and drive will not work. )

 

[tspope]

modem7 thank you so much for your time and the direction on this. This answered all of the questions I had and will get me going further in the right direction. I am really looking to get this unit back as close to October 1981 as possible. Glad to have found these resources and VCFED. We must protect you at all costs!!!

I will circle back around soon!

 

[tspope]

Hi M7,

Just circling back around here. I am awaiting the U33 RDR and 10/82 revised BIOS which should arrive Monday.

For now I am operating with a 16-64 mb with nothing in U33 socket. Original PSU with fan running, on for minutes with no problem and all voltages matching.

A couple steps I've made in meantime as I wait --

I have removed 8087 chip. Adjusted sw1 to reflect this.

I have removed RAM chips in bank 1, 2 and 3. Adjusted sw1 to reflect this.

Starting up with minimal config -- PSU + mb + speaker -- still no beeps

Starting up with minimal config -- PSU + mb + speaker + mda card & 5151 -- monitor (tested working) not displaying anything -- no cursor.

I tried to hook up only PSU and TM100-1 to see if I'd get any kind of feedback from the drive and other then a feint flicker of the red light on power up nothing else.

I tested the 5v and 12v rails on mb according to minus 0 d and everything appears to match as expected. Also tested the female memory sockets for banks 1, 2 and 3 and they are as expected.

Motherboard is very clean. There is very minimal greenish oxidation in some areas as well as 1 or 2 of the removable memory chips appearingly darkened/burned looking on pins.

The trimmer T1 for the cga also appears in tact but a slight darkening/burn looking on the metal ring under the green dial.

Also the MDA card i mentioned in first post I dont believe to be the original -- the rail is not wide and black like the original cga and fdd cards. Not sure if this matters.

I am hoping popping in the RDR will Frankenstein this thing up off the table. Just looking for a sign of life.

 

[modem7]

For now I am operating with a 16-64 mb with nothing in U33 socket.

Starting up with minimal config -- PSU + mb + speaker -- still no beeps

Starting up with minimal config -- PSU + mb + speaker + mda card & 5151 -- monitor (tested working) not displaying anything -- no cursor.

I tried to hook up only PSU and TM100-1 to see if I'd get any kind of feedback from the drive and other then a feint flicker of the red light on power up nothing else.

Those three tests require a functional IBM BIOS ROM in socket U33.

Also the MDA card i mentioned in first post I dont believe to be the original -- the rail is not wide and black like the original cga and fdd cards. Not sure if this matters.

No, it doesn't matter.

I am hoping popping in the RDR will Frankenstein this thing up off the table. Just looking for a sign of life.

Be sure to have your fingers crossed when you flick the red switch.

 

[tspope]

So I got the RDR chip in early -- seated and minimal start -- building excitement

no beeps.

I did not try the 10/82 revised bios I also ordered. I'm assuming the speaker works... it tested for continuity.

I double checked the P8 and P9 voltages when plugged into the MB and they are stable and matching -0d writeup. Power Good is around 5v. I took measurements on the memory 0-3 bank rails and they all appear to be +-5v and +-12v around the tantalums.

I don't have any of the other diagnostic tools (logic or oscilloscope) or really any spare parts to cross check -- but still following https://minuszerodegrees.net/5150_5160/diag/IBM 5150 and 5160 - Faulty motherboard symptom.htm.

This is the makings of what may turn out to be an expensive hobby. Wifey is starting to look at me wondering when this project will be relocated out from her living space but I'm not ready to throw it all away just yet!

 

[seaken]

Yeah, that's why a lot of us have our lab in the basement. The upstairs remains the wife's domain and she has boxes of antique glass on the floor. She can't really give me the stink eye when she comes down to my lab and sees the open computer cases all over the place

Seaken

 

[modem7]

This is the makings of what may turn out to be an expensive hobby.

If I buy a vintage car, what is my plan for when it breaks down? (When, not if.) Money is needed, whether my plan is to get a professional in to repair the vehicle, or I buy test gear and spare/replacement parts. If the latter, how far do I go with that?

I don't have any of the other diagnostic tools (logic or oscilloscope) or really any spare parts to cross check ...

Yes. Obviously, without those, you can only go so far down the diagnosis path.

So I got the RDR chip in early -- seated and minimal start -- building excitement

no beeps.

I did not try the 10/82 revised bios I also ordered.

Definitely try the 10/27/82 BIOS, in case of a problem with the RDR ROM. (Surely both ROM's can't have been improperly created.)

 

[modem7]

To give you an idea of what I (with the luxury of test equipment and spares) would do, if I was given your motherboard:

1. Something quick: Try a known-working ROM (either IBM BIOS ROM, or RDR) in socket U33. 'Known-working' = it works in another motherboard.
2. Something quick: Carefully remove the Cassette BASIC ROM's. Not needed for RDR operation. Not required for the 10/27/82 BIOS to start and display something on-screen.
3. Something quick: Try a known-good power supply, in case the problem is caused by an inadequate delay in the POWER GOOD signal.
4. Something quick: Use my multimeter to verify that the reset pin on the 8088 CPU is not sitting at a HIGH level (i.e. not being released from the reset state).
5. Using my oscilloscope, verify proper production and distribution of clocks.
6. Using a logic probe, go though the first 9 steps of [here].

And so on, as required.

Related to action #3 above. There is something you can try. Power on the 5150, then, whilst the 5150 is running, momentarily ground the POWER GOOD line. If you then see the computer booting on-screen, it means that the problem is probably related to the delay of POWER GOOD generation.

 

[modem7]

... and it had an updated U33 BIOS chip which I managed to bend/break the pins pulling out (embarassing) ...

Dirty/tarnished contacts now in the U33 socket ?
Try removing/refitting the RDR ROM a few times.

 

[tspope]

I have a 5151 (working) plugged into the PSU and the MDA card and sw1 set. On startup its dead, no cursor, lighting or anything. I just checked the PSU output for DC voltage black in ground. I am getting close to nothing on the left prong and weird fluctating erratic voltages 3v on the right. Shouldn't these be higher to power the 5151? Weird.

I test 8088 pin 1 and reset and it spikes to around 3v on startup and drops and stays low maybe .11v steady so if i did it right I don't believe it is getting stuck in reset mode.

I wanted to try and ground pin 1 PG Power Good but I am not sure how to using the multimeter. If its a matter of just plugging the PG and gnd with the probe and disconnecting, that didnt seem to do anything.

Would it be worth it to open the original 63.5w and inspect ?

I don't think I want to mess too much with the socketed chips as its an old original machine and they are a pita to perfectly remove. I may be reaching unchartered waters here. Is there any good resources here in NJ if I can't get it going ?

 

[tspope]

I realized it should have been tested in A/C and it is 121v so I guess thats correct and needing 120.

 

[modem7]

I have a 5151 (working) plugged into the PSU and the MDA card and sw1 set. On startup its dead, no cursor, lighting or anything. I just checked the PSU output for DC voltage black in ground. I am getting close to nothing on the left prong and weird fluctating erratic voltages 3v on the right. Shouldn't these be higher to power the 5151? Weird.

The photos show that the cause of the strange readings is that you have the multimeter in DC voltage mode, not AC voltage mode.

I test 8088 pin 1 and reset and it spikes to around 3v on startup and drops and stays low maybe .11v steady so if i did it right I don't believe it is getting stuck in reset mode.

That sounds good. Provides confidence.

I wanted to try and ground pin 1 PG Power Good but I am not sure how to using the multimeter. If its a matter of just plugging the PG and gnd with the probe and disconnecting, that didnt seem to do anything.

Here is one way:
Use a piece of wire.
Connect one end to a ground, an exposed metal part of the chassis.
The other end of the wire you would hold, then momentarily push that onto the POWER GOOD contact within the P8 connector.

If required, you can use the multimeter to do this, by putting the meter in current measuring mode. Looking at the photo of your meter, move the red lead to the '10A' socket, then change the measurement setting to 'A'. After that, there is low resistance between the two probes.

Is there any good resources here in NJ if I can't get it going ?

Hopefully someone may comment.

 

[tspope]

Just as a little back story to add to the case file -- this machine was working or was posting prior to purchase. The knucklehead shipped everything in 1 box and the 5151 arrived in pieces. It wasn't exactly handled with care and I am not sure if anything else was damaged in transit but I havent been able to get a beep or see a cursor since.

So, the no quit in me kicked in and i decided to remove all Casette Basic chips at u29-u32, started up and nothing. Since reseated them.

Removed all memory bank and bit chips and again tested all sockets for -5, 12 and 5 and it all checked out. I tested bank 0 and got the same. (I shorted something testing bank 0 and lost voltage to everything, had to reboot the machine and everything good again but we can pretend that didn't happen).

Removed 8088 processor and reseated.

Also tried both RDR (currently installed) and 10/82 BIOS at U33 which a member from here programmed for me.

I took your advice and reconfigured the multimeter as directed to cause a temporary ground to Power Good. I am not sure if I am doing it right but i placed the black probe under a screw that secures the cards to the frame. Then booting up the machine, within a second or 2 of boot up, pushing the red into PG briefly and pulling it out. Other then a quick reading of .9 or .10 volt on the multimeter -- nothing more. Tried 2 or 3 times. I considered repositioning the black probe into the ground wire/slot of the molex connector instead but held off -- not sure if it would make a difference.

P8
PG +5v
+12
-12

P9
-5, +5 +5 +5

Ive attached pictures of the current mb config. Visual inspection looks ok but I cant see under the floppy/hd caddy because I tried doing this still in the case.

I've been going through the endless resources at m0d and the forum here and learning more and more. I think I am now close to the point of needing to buy more testing equipment.

Every day I walk away from it and come back to get a little closer to figuring this one out. I appreciate your support, guidance and time helping me.

 

[docangle]

I recently started working on these boards, I have learned a lot in a short amount of time. I would say at this point you will need at minimum a handheld Oscilloscope and an inexpensive soldering kit if you don't have one. You can get these items for cheap on Aliexpress or Amazon if you prefer. You will need to check if the system is generating a 4.77 Mhz clock, you will need to short pins and do the IO Ready Test procedure, after that it is more than likely a Logic Chip issue. You just need to follow testing procedures to find out which one it is. These chips are inexpensive, but changing the chips out on these boards require patience, as they are really well made. Trying to desolder these chips with desoldering wick is difficult due to the thick copper core of these MB's. If you don't have a desoldering Iron, I would cut each leg off the chip near the top of the chip so it leaves most of the legs left so you can use your iron underneath and a small plier gently pulling on the leg from the top(I know all of the experienced people on this site are cringing at this, but for a noob it is the simplist method, even though you are destroying the chip). Clean up with desoldering wick and alcohol. Desoldering needles are cheap and can help open the holes if you can't clear them using desoldering wick. The soldering pads on these MB's are supper strong (not like Mac Logic Boards) but you do want to be carefull with the traces, you don't want to damage them or expose them (if you do remove the protective layer, I would just add clear nail polish once you clean them up). Their are a lot of Youtube Videos showing the process of removing thu-hole chips and resoldering in new ones.

Also, you may want to remove the motherboard and power supply from the case to allow you to easily access the MB. Their are only two screws holding the MB in place (one near Power Supply connector and one on the front half way up. Once you remove the power supply connectors and speaker connector the board will slide out, it is a little fiddly due to the plastic stand offs which are sitting in key ways. The Power supply is help in by four screws on the back and you slide it forward slighty and lift out. Make sure you put MB and power supply on a static free surface when operating.

I know it seems daunting, but if you stick with it, and you figure out the issue, when you turn on the machine and it fires up into RUUD's ROM, you will be rewarded. In my case it lead to purchasing another 5 of these machine just for the fun of getting them to work. The minimum repair equipment needed can be used for alot of small repair work around the house and car, so it is really a good investment.

 

[tspope]

I recently started working on these boards, I have learned a lot in a short amount of time. I would say at this point you will need at minimum a handheld Oscilloscope and an inexpensive soldering kit if you don't have one. You can get these items for cheap on Aliexpress or Amazon if you prefer. You will need to check if the system is generating a 4.77 Mhz clock, you will need to short pins and do the IO Ready Test procedure, after that it is more than likely a Logic Chip issue. You just need to follow testing procedures to find out which one it is. These chips are inexpensive, but changing the chips out on these boards require patience, as they are really well made. Trying to desolder these chips with desoldering wick is difficult due to the thick copper core of these MB's. If you don't have a desoldering Iron, I would cut each leg off the chip near the top of the chip so it leaves most of the legs left so you can use your iron underneath and a small plier gently pulling on the leg from the top(I know all of the experienced people on this site are cringing at this, but for a noob it is the simplist method, even though you are destroying the chip). Clean up with desoldering wick and alcohol. Desoldering needles are cheap and can help open the holes if you can't clear them using desoldering wick. The soldering pads on these MB's are supper strong (not like Mac Logic Boards) but you do want to be carefull with the traces, you don't want to damage them or expose them (if you do remove the protective layer, I would just add clear nail polish once you clean them up). Their are a lot of Youtube Videos showing the process of removing thu-hole chips and resoldering in new ones.

Also, you may want to remove the motherboard and power supply from the case to allow you to easily access the MB. Their are only two screws holding the MB in place (one near Power Supply connector and one on the front half way up. Once you remove the power supply connectors and speaker connector the board will slide out, it is a little fiddly due to the plastic stand offs which are sitting in key ways. The Power supply is help in by four screws on the back and you slide it forward slighty and lift out. Make sure you put MB and power supply on a static free surface when operating.

I know it seems daunting, but if you stick with it, and you figure out the issue, when you turn on the machine and it fires up into RUUD's ROM, you will be rewarded. In my case it lead to purchasing another 5 of these machine just for the fun of getting them to work. The minimum repair equipment needed can be used for alot of small repair work around the house and car, so it is really a good investment.

I am in my early 40s and my first PC was a 386 IBM-compatible in the late 80s early 90s -- dialing into BBS -- so the 5150 definitely preceded my era. These machines while seemingly limited by today's standards are still very fascinating. It started because I am a vintage junky and came into an early untouched unit which turned out to be a REV A 5150, 5151, 5152 and model F keyboard (w/ metal connector) including the 5700051 chip, Advanced Diagnostics 1.0 floppy and cassette, DOS 1.0 -- the whole suite of first editions and only really missing the original SS tandon tm-100 dated in 81 which I am still looking for -- A beautiful near complete relic and one that I decided to just preserve and put away... but I learned a lot about it since.

It didn't stop there and here I am again with another machine -- LOL -- my new project here that's got me pushing the envelope and I'm already one leg in the rabbit hole. I've been prepping myself watching a lot of videos of the soldering process including the removal step with the tool to punch out the joints. If this particular 5150 wasn't another real early model I'd be more comfortable practicing on it. I really appreciate the feedback and I think my gameplan will include buying a Oscillioscope to try and narrow down the areas of failure and go from there. If I can't repair it I would like to find someone that can or part it out to someone that will bring it back but I am not at that point yet. Maybe moving forward I will end up like you with 5 more machines to tinker with. It's sure looking that way especially seeing how important it is to have working good parts to test with -- which I don't. Bringing these things back to life is definitely rewarding and damn if I could get something on screen or boot into RDR -- It would be amazing.

Thank god for the abundance of information out there relating to these machines -- VCFED, m7, Minus -0 Degrees and everybody else that has committed their time to the preservation of the hobby and us newbies that share the same intrigue. I am already thinking about attending one of the east coast VCFED functions and I'm following on Facebook. Drinks on me!

 

[seaken]

Yes, I highly recommend the VCF East festival in the spring. Well worth it.

Do you have a surplus store near you? We have one nearby us and I am able to pick up some scrap PC boards for practice. Pick up some old trash boards and use them for practicing your soldering and chip removal etc. I got this tip from here on VCF and it has helped me a lot. Even if you have to travel a bit to pick up some scrap. Unfortunately most recycling centers won't let you grab old trash equipment around here (Mid-Hudson Valley) and you may not have a nearby surplus store with this kind of stuff. But check it out.

Seaken

 

[docangle]

Yes, I highly recommend the VCF East festival in the spring. Well worth it.

Do you have a surplus store near you? We have one nearby us and I am able to pick up some scrap PC boards for practice. Pick up some old trash boards and use them for practicing your soldering and chip removal etc. I got this tip from here on VCF and it has helped me a lot. Even if you have to travel a bit to pick up some scrap. Unfortunately most recycling centers won't let you grab old trash equipment around here (Mid-Hudson Valley) and you may not have a nearby surplus store with this kind of stuff. But check it out.

Seaken

Definitely worth a trip if you can find one. Until I started my latest trend on IBM 5150’s I had mostly been working on ver late 80’s and early 90’s Macintosh machines, they mostly used surface mounted chips and SMD capacitors, so I mostly used my hot air workstation, thru hole components were mainly for the Power Supply. I was very rusty, and again these boards are thick and love to disperse the heat from an iron.

But don’t give up, stick with it, you will figure it out. More than likely it will be Something in the lines of U8, U12, U13 or U14, as long as you have a good clock frequency from the clock generator. These data lines are critical to the BIOS and Bus. Again it is not guaranteed these specific chips are the issue which is why Modem7 will tell you that you need to run IO Ready test, to make sure these chips are showing the proper high and low signals. These are Logic Gate Chips. Think of them as Water Faucets, but can flow in both directions. If they get stuck in high or low or vice vera, it will cause the CPU to halt the system (it is a little more technical). I would also download the IBM 5150 Technical Manual, it has a lot of great information, look at the schematics involving the BIOS. I would also look up reading schematics on YouTube, it will help you understand how to read them, so you can understand what pins on a specific chip should be high or low. It helped me figure out one of my MB’s I was struggling to fix.