Microelectronics | COMPAQ Prolinea 4/66

Synopsis

My first PC was constructed around a proprietary desktop case and an AT clone mainboard specifically designed for it. Back then, I had friends who had completely generic PCs based on standard AT-class mainboards and normal (mostly midi-) tower cases. Other friends had proprietary PCs made by IBM, Dell, Packard Bell, or Compaq. I was in the middle of both worlds. I always liked the flexibility and modularity of generic PCs, but I was attracted by the fact that proprietary PCs just worked. People who had them rarely felt the need to upgrade them or switch components and assemblies. In some cases, there was quasi-nothing to update -- think about MCA bus IBM PCs.

In time, I migrated to generic PCs that I assembled all by myself and never looked back. But somewhere in my soul I sought after one of those proprietary 1990s PCs. Over time, I had a few, but somehow I parted with them for one or more reasons. Of them all, I remember mostly the IBM PC 350, the Packard Bell Legend series (which sometimes had a Multi-Media badge instead of the model number), and the Compaq Prolinea 4/33.

While I had both IBM and Packard Bell machines (I wish I hadn't sold them 20 years ago), I never had a Prolinea series PC. Thus, I searched for one of these Compaq branded desktop units for quite some time but failed to find one in good condition. With time, I lowered my expectations and finally found one, albeit in a poor optical condition. The good thing is that the mainboard is in pristine condition, and the power supply is still working. But overall, I think this was the dirtiest PC that I ever bought.

Other than nostalgia, I don't have an immediate use for such a PC. However, I already see it as HP-IB controller on a rack shelve, next to my Hewlett-Packard test instruments. I already have an ISA HP-IB interface that is now installed in another machine. I plan to move it to the Compaq computer. Well, now I have given some weight to this project. In addition, the appearance of this desktop unit relates to the old HP design language.

Without further talk, let's skip directly to the restoration.

Maintenance

Besides a good clean, I would like to preventively replace electrolytic capacitors on the mainboard and the power supply. I will also replace the power supply fan with a modern low noise part. Additionally, I'd like to max out the RAM and install a network card. And maybe I will replace the CPU.

Machines of this type are often very simple and easy to work on. Possible issues and unpleasant surprises might be caused by rust or broken plastic parts. This unit suffers from both of them. Good thing is that the two broken plastic tabs were floating around inside, and I was able to glue them together with the front bezel.

Cleaning the Case

As soon as I opened the cardboard box, I was greeted by the most dirty PC that I ever had. Besides the decades of dirt, the case is fairly scratched. On the inside, there are some rust spots. Thankfully, there's no rechargeable battery in this system. Otherwise, it would've leaked for sure, damaging the mainboard and the case. This particular revision of the mainboard has a soldered BR2335 battery, and these don't leak.

Anyway, I dismantled everything and washed the case with soapy water. The plastic parts cleaned up pretty well. But the scratches on the metal case became more apparent. I think that I will have to respray the case.

I am thinking about using a corrosion inhibitor on the rust spots inside the case. Until then, I'll leave them like this as they will not extend in a humidity-controlled climate. Somebody had some really greasy fingers and left these ugly stains on the front steel panel. If I ever decide to respray the internals, I will have to clean the metal thoroughly.

I added a personal touch to the status indicators: green for power and orange for HDD activity. Both LEDs were initially matte green. Furthermore, the power LED was dimmer than the HDD activity LED. This indicates a lot of power-on hours.

Then I washed all other mechanical parts and the results were relatively good. Again, with the mention that in the future I might respray some of the inner metal parts. The front bezel came up pretty clean. There's something very retro about those round LED light pipes.

Let's advance to the next operation.

Mainboard Maintenance

Next, I washed the mainboard with soapy water. After I blew away the excess water with compressed air, I let the board in the sun for the rest of the day. It turned out like new.

The PCB is relatively small and effectively crowded with components. Thankfully, there are only two electrolytic capacitors, both in non-critical positions. They are used as part of the audio circuit section. The probability that these parts will ever cause any issues if damaged, is close to zero. But since I have the PCB out, let's replace them anyway.

COMPAQ Prolinea 4/66 Mainboard
Identifier	Value	Qty	Notes	Mouser Number
C504, C509	100 uF / 35 V	2	Polymer Capacitor	80-A759KS107M1VAAE31

These capacitors are located next to a TDA7052 mono audio amplifier integrated circuit. Inspecting the datasheet reveals that this IC does not require an output coupling capacitor. So I think they might be used for local power supply ripple filtering. But it makes me wonder why a 35 V rating? I don't know what that Compaq rebranded chip does, but I'd suspect it might also be part of the audio circuitry, though I cannot find any datasheet. I'm curious whether it's a logic IC or some kind of analog (pre)amplifier circuit. By comparison, there is a LM324 quad op-amp IC that has a tiny package.

Later edit: I probed the circuit traces around those two capacitors with the multimeter. It was revealed that the plus terminals connect to individual pins on the Compaq branded IC discussed above, while the minus terminals connect to the amplified audio output connector. Thus, mystery solved: these are output coupling capacitors, and the Compaq branded chip is a stereo audio amplifier.

Anyway, here's a picture of the replacement capacitors already installed. If you have a similar board, then there's no point in replacing these parts. Unless they have leaked.

Before moving on, let's measure the old capacitors. I suspect they are in good condition.

CAPACITOR DATA
Brand	Type	Style	Rating	Capacity	ESR
Nichicon	Electrolytic	Radial	100 uF / 35 V	100.5 uF	0.74 Ω
Nichicon	Electrolytic	Radial	100 uF / 35 V	101.3 uF	0.95 Ω

These capacitors were perfectly fine. For the record (and the sake of science), the new polymer capacitors measured as follows.

CAPACITOR DATA
Brand	Type	Style	Rating	Capacity	ESR
Kemet	Polymer	Radial	100 uF / 35 V	100.0 uF	0.22 Ω
Kemet	Polymer	Radial	100 uF / 35 V	100.4 uF	0.25 Ω

Besides the even lower ESR of the polymer capacitors, the capacitance matches what's printed on the aluminum cans. I measured a lot of other new electrolytic capacitors, and almost all of them read between 15 to 20 % lower capacitances than advertised. Anyway, in this circuit implementation, the ESR of the output coupling capacitors is not that important, 0.74 Ω and 0.95 Ω being perfectly acceptable. In addition, I will mostly not use the amplified audio output.

The next step is to solve the issue with the battery. Replacing a soldered BR2335 lithium carbon-monofluoride battery would've discouraged most users back in the late '90s when these products were approaching the end of their usable life cycle. Well, it kind of annoys me too. My initial thought was to bypass the battery and make use of the optional external battery pin header. But then I thought that a 3 x AAA battery holder would look a bit out of place. Why not add a standard CR2032 battery holder, instead? Surprise! I couldn't find any with that 3-terminal disposition. For a second, I thought about making my own interposer PCB. But that would've taken far longer than the time I had allocated for this project. Thus, I ordered a CR2032 and a CR2450 battery, both equipped with 3-terminals for PCB mounting.

Solderable CR2032 and BR2335 batteries have slightly different terminal rasters, but with a bit of care, a CR2032 does fit the mainboard holes. Finally, I installed the larger capacity battery since it was a direct fit. In addition, it should give me a few years of trouble-free operation. In the meantime, I might just craft that interposer PCB.

After the battery replacement episode, I reinstalled the mainboard in the case and inserted the ISA riser card that I had previously washed with soapy water. The empty slot on the right is for a proprietary cache module.

These are hard to come by, and at this point, I am absolutely at peace with the thought of never finding a cache card for this mainboard. Nor any VRAM extension board. Thus, let's move on.

Power Supply Maintenance

The classic AT-style power supply is a 145 W unit. The electrical and mechanical construction is of good quality and the components are mostly from reputable manufacturers. The amount of fine dust present in the PSU reveals that it has been turned on for extended periods of time in a harsh environment. Possibly a school in the countryside.

First, I washed everything with soapy water. After drying up, I proceeded to inspect the unit. As with any old power supplies, I checked for the dreadful RIFA capacitors. Thankfully, there were none. Most of the electrolytic capacitos are made by Chemi-Con, but there are some smaller ones from obscure brands.

Next, I removed all electrolytic capacitors.

The following list contains the parts that are due for replacement. The red line below doesn't need to be ordered. I installed that specific capacitor in order to provide some extra local ripple filtering for the fan circuit control. While this may sound like overengineering, the PCB has provisions for such a capacitor.

COMPAQ Prolinea 4/66 Power Supply
Identifier	Value	Qty	Notes	Mouser Number
C101	3.3 uF / 450 V	1	Electrolytic Capacitor	667-ECA-2WM3R3
C102, C103	470 uF / 200 V	2	Electrolytic Capacitor	647-LGR2D471MELZ40
C204, C212	220 uF / 25 V	2	Polymer Capacitor	80-A755KS227M1EAAE25
C205	1200 uF / 16 V	1	Polymer Capacitor	647-RNL1C122MDSBSQ
C206, C207	3300 uF / 16 V	2	Electrolytic Capacitor	661-EKY160ELL332MK3
C301	47 uF / 50 V	1	Electrolytic Capacitor	710-860040673002
C305, C601, C603	4.7 uF / 50 V	3	Electrolytic Capacitor	710-860160672005
C306, C403, C702	10 uF / 50 V	3	Polymer Capacitor	80-A759BQ106M1HAE105
C501, C502	47 uF / 25 V	2	Polymer Capacitor	80-A750EK476M1EAAE40
C801	10 uF / 50 V	1	Polymer Capacitor	80-A759BQ106M1HAE105
C803	100 uF / 25 V	1	Polymer Capacitor	80-A755KS107M1EAAE25

I normally select replacement capacitors from the same manufacturer for all of my projects. But for this power supply, I just picked up whatever I quickly found while browsing the Mouser parts catalog. Besides the well known brands, this time I also picked up some Würth Elektronik branded capacitors. I don't know whether they're good or not, but at least they are new. I guess time will tell if I did the right thing.

Let's take a look at the measured parameters of the old capacitors. Again, I suspect they are in good condition.

CAPACITOR DATA
Brand	Type	Style	Rating	Capacity	ESR
A.M.	Electrolytic	Radial	3.3 uF / 450 V	2.02 uF	391 Ω
Chemi-Con	Electrolytic	Radial	3300 uF / 10 V	2982 uF	0.03 Ω
Chemi-Con	Electrolytic	Radial	3300 uF / 10 V	2987 uF	0.03 Ω
Chemi-Con	Electrolytic	Radial	1200 uF / 16 V	1101 uF	0.08 Ω
Chemi-Con	Electrolytic	Radial	220 uF / 25 V	206 uF	0.66 Ω
Chemi-Con	Electrolytic	Radial	220 uF / 25 V	209 uF	0.65 Ω
Chemi-Con (one broken leg)	Electrolytic	Radial	100 uF / 25 V	-	-
Chemi-Con	Electrolytic	Radial	47 uF / 50 V	41.97 uF	2.49 Ω
Marcon	Electrolytic	Radial	470 uF / 200 V	417 uF	0.12 Ω
Marcon	Electrolytic	Radial	470 uF / 200 V	438 uF	0.12 Ω
Marcon	Electrolytic	Radial	10 uF / 50 V	9.40 uF	13.59 Ω
Marcon	Electrolytic	Radial	10 uF / 50 V	9.50 uF	13.10 Ω
Marcon	Electrolytic	Radial	10 uF / 50 V	9.58 uF	9.18 Ω
Marcon	Electrolytic	Radial	4.7 uF / 50 V	4.15 uF	9.06 Ω
Marcon	Electrolytic	Radial	4.7 uF / 50 V	4.60 uF	7.94 Ω
Marcon	Electrolytic	Radial	4.7 uF / 50 V	4.64 uF	8.00 Ω
Rubycon	Electrolytic	Radial	47 uF / 25 V	44.60 uF	2.38 Ω
Rubycon	Electrolytic	Radial	47 uF / 25 V	45.20 uF	2.36 Ω

As expected, almost all capacitors are in good condition. Diving into the history of the Marcon capacitors reveals this brand was owned by Toshiba. Then it was bought by Chemi-Con, back in 1995. No wonder they still measure good.

There was some glue under that 100 uF / 25 V capacitor, and even if the legs were freely moving in their holes, the hardened glue secured the capacitor firmly to the PCB. While pulling the part, one of the legs broke free from the inside of the capacitor, and remained stuck in the glue. Anyway, being a Chemi-Con, I suspect it was probably measuring good.

The surprise came from that A.M. branded electrolytic capacitor. It measures bad and, of them all, it's the only one that's slightly bulged. I've never heard of the A.M. capacitor brand, but I guess it's a garden variety part.

Here's the power supply PCB with the new capacitors installed.

An interesting fact is that some of the components are made by Lite-On.

The PCB is pretty much crowded with parts. The designers probably ran out of space as there are miniature 0.125 W resistors even under some capacitors.

There are some missing components (as in never installed). I guess this PCB was shared between multiple variants of power supplies. But nevertheless, the components are of good quality. I haven't seen any low voltage ceramic capacitor; all of them are of MLCC type.

The original fan is still in good condition, albeit very dirty and noisy. But the bearings are still OK. I decided to replace it with a 12 V Noctua NF-A8FLX fan. As an HP-IB controller, I'd disconnect the magnetic hard disk drive, and combined with a CF card, this PC would be totally silent.

And here is the completed PSU assembly.

The power supply restoration was straightforward and easy to accomplish. The machine can now be left powered on without any supervision as the risk of something blowing up or catching fire has been greatly reduced.

Floppy Disk Drive Repair

The floppy disk drive was dead on arrival. In addition, somebody removed the data transfer cable. Also, the floppy disk compartment was stuffed with some sort of folded paper remnants. After I removed those and blew the dust away, I connected the drive to the mainboard. When I tried to access the disk, it produced successive I/O errors. Well, it looks like this repair is another mini-project of its own.

The drive is model MPF 420-4, made by Sony, and it has that proprietary Compaq look and feel. In the past, I have had mixed results repairing floppy disk drives. While I don't have high hopes, I decided to give it a try anyway. This is a quality drive, and if it can be fixed, then it's a nice collectible artifact from the early '90s.

First, I disassembled the unit and washed the logic board with soapy water. Then, I replaced the sole electrolytic capacitor. It was a 47 uF / 16 V part, which I replaced with an OS-CON 56 uF / 25 V polymer capacitor. The capacitance value is non-critical as it's used for local +5 V rail filtering purposes.

I disassembled all the mechanical components and I washed them with soapy water. The chassis is made of die-cast metal. I didn't know how to remove the spindle motor (in fact, the large permanent magnet flywheel, and its floppy interface hub) from the chassis, so I carefully cleaned around with extra care.

Next, I cleaned the head assembly and the two magnetic heads. I lubed the head block sliding rail and reattached the assembly to the chassis. I also cleaned the stepper motor that moves the head block over the disk surface. I lubed the bearings with PTFE spray and installed the motor back on the chassis. The track 0 optical sensor is bolted to the chassis in the upper right section. The two oval holes are for track 0 position fine-tuning.

Then, I assembled the rest of the unit, adding the floppy disk sliding metal cage and the side reinforcing rails together with the two eject springs. I lubed everything with quality grease. Finally, I reconnected the track 0 optical sensor and the two magnetic heads to the logic board.

Eager to test the unit, I connected it to the mainboard and started the PC. The drive was detected, and the initialization seeking sequence was performed. I tried to read a floppy disk, but I got successive errors, claiming hardware fault while reading the drive. After many (twenty, thirty, maybe more) retries, I was able to persuade Dos Navigator to switch to drive A and report the total free space on the test disk, and surprisingly, it was correct. But no data was read back from the disk.

I launched MSD DiskDupe, and I was able to issue the clean command, which was completed successfully. The total time spent was around 15 seconds. Any other command I tried, failed with a 202 error, stating that the address mark was incorrect. As I said, repairing floppy disk drives without adequate alignment equipment is a trial and error game. I suspect either the head block is misaligned, or there is some other mechanical issue. I don't think the electronics are fried, as the free disk space was returned correctly, albeit I managed to access the drive only once.

I tried Norton Disk Doctor and to my surprise, it succeeded in reading and diagnosing a floppy disk to a certain extent. It failed quickly, nonetheless, but it went farther away than any other program I have tried. It was the only program that attempted to raw read the floppy disk despite the fact that no data was returned. The software moved the head block back and forth, seeking for something. Interestingly, there were no track 0 bad errors. To me, this sounds exactly like a track 0 sensor issue.

The drive doesn't make any strange noises. The spindle motor is smooth, powerful, and nearly silent, while the head block stepper motor sounds better than most modern floppy disk drives. Oh well, at least I tried. This was not a repair per se, but mostly a cleanup and lubing of the mechanism. Maybe I will get back to this drive in the future and try to better diagnose it for a more serious repair.

Finding a replacement drive compatible with the Compaq design language is a challenge. Fortunately, I was able to find one locally. I got it almost for free. It's a Citizen branded drive, but it has Compaq stickers, and it fits the front bezel like a charm. Judging by the appearance, it's a newer unit, probably made in the late '90s or even the early 2000s.

It also came with a connection cable that has a wrong hardware key; at least it's not compatible with the floppy header on the mainboard. In addition, the cable is way too long for this PC. I plan to cut it and terminate it with new 34-pin Harting connectors.

I've put the Sony MPF 420 unit aside for a bit, and switched my attention to the Citizen drive. The spindle motor metal bracket has some corrosion which I cleaned with the Dremel tool and a wire brush. Other than that, the unit is in good working condition, albeit dirty and dusty.

I washed, cleaned, and lubed the Citizen drive and prepared it for installation. But before mounting it on the steel plate carrier that bolts to the PC chassis, I decided to give the Sony drive another try. I searched the Internet for the technical manual, hoping to find some alignment procedure documentation on the MPF 420 series. I failed to find any, but I found something else instead. It's interesting that I can switch the color of the front LED between green and amber. I chose amber.

I used the ISA Signal View Interface to monitor the drive read and write activity, IRQ6, and DMA2. Then, I wrote a simple program in assembly language to turn the floppy drive motor on. Since this drive doesn't reset the heads to track 0 when a new floppy disk is inserted, I quickly extended the program by adding functionality to move the heads to a specific track.

I fired the HP 16500C unit and loaded the oscilloscope module. I connected the probes to the magnetic head signals and tuned the optical track 0 sensor up until I received the highest amplitude reading. The procedure was as follows.

Turn spindle motor on.
Move heads to middle of the disk (track 40).
Carefully adjust track 0 sensor based on the last observed amplitude of the signal.
Move heads to track 0.
Observe the amplitude of the signal.
Repeat steps 2 through 5 until the amplitude is maxed out.
Turn spindle motor off.

Finally, I secured the sensor with the screw and rebooted the PC. Surprise, the floppy disk drive came to life, completely. This was a tedious operation but it worked. Well, now I have the Citizen drive as spare.

This repair took longer than I expected, but after all, I'm glad that I solved the floppy issue, one way or another.

Future Plans

Since clock-doubled 486 CPUs greatly suffer from the missing L2 cache, I'd like to source a 486DX / 50 MHz CPU, and use that one instead. There might be some stability drawbacks, but I will strive to overcome those. Hopefully, the chipset and the peripherals on this mainboard can cope with the 50 MHz CPU clock. Or I could jump directly to a Pentium Overdrive running at 83 MHz. That should be an interesting upgrade.

If I find sufficient motivation, I could design my own implementation. According to the documentation, the original cache board was constructed around the SONY Cache-2 single chip cache subsystem. This is a SONY ASIC that goes by the CXK784862Q-33/50 indicative. A Pentium Overdrive CPU with 256K L2 cache would run Duke 3D flawlessly.

I am also thinking about a method to restore the case badge. The red paint is chipped, but the substrate is pristine. Maybe it can be reworked with some translucent vitrail paint.

Finally, I am thinking about respraying the outer metal case. And possibly the chassis. I'm not sure if I should do it myself, or go to a paint shop.

Curiosities

The internal mainboard documentation actually lists this machine as a Deskpro XE instead of a Prolinea. Furthermore, the Compaq Inspect program also reports the machine as a Deskpro XE. This leads me to think that these models were pretty similar and were produced in parallel.

The designers went wild with the video section. They used a little known Motorola video controller chip that goes by the name of XC02SH007NS07. Compaq video cards using this (or variations of the) chip are called QVision number/indicative. I think that the number represents the maximum X-axis video resolution that the card is able to display. The indicative can be either I, P, or E, corresponding to internal (ISA), PCI, or EISA. I'm not sure if VLB was an option.

I did some research, and there are some standalone Compaq QVision 1280/P PCI graphics cards based on the Motorola XC02SH007NS08 chip. It makes me wonder if these chips are identical, besides the bus interface signaling. However, the Compaq Inspect program reports that this machine contains the QVision 1024/I graphics controller, and a total of 1024 Kb of video memory.

Anyway, whoever did the PCB layout had a different view on the symmetry concept. Take a look at those four pin headers next to the video RAM chips. If I were to design a DIY VRAM extension board, I would have a hard time measuring around with the precision caliper. I can understand that aligning the headers this way accounts for a foolproof insertion of the RAM extension board. But I've seen better designs -- Matrox, anyone?

Furthermore, there's no real estate issue as the mainboard is a 6-layer PCB. So they had all the space they needed to route the wires, which I think are software autorouted, anyway.

The interesting part is that the video processor burns hot to the touch. Since most of the early 1990s video cards run cool, I wasn't expecting this. I ended up adding a heat sink bound with adhesive thermal tape.

Don't get me started on the cache RAM support. They used this weird PCI-like brown slot that accepts a proprietary cache card containing the SRAM and the cache controller logic within the same proprietary chip. Well, it is almost like they didn't want this machine to ever be user upgraded. 486 chips, and especially clock-doubled (or -tripled) ones, such as the DX2 or DX4, suffer great performance losses without cache. In my opinion, such a system without cache would better work with a 486DX / 50 MHz.

By soldering the battery on the mainboard, the designers sent a clear message that these systems are not user-serviceable. They still provided an external battery header and associated configuration jumper though. At least they didn't use any rechargeable batteries. Anyway, hobbyists will always find ways to overcome original design limitations. As I previously said, I can craft an adapter (interposer) PCB with a CR2032 battery holder. But I'm not sure if it's worth it. It's easier to solder a new BR2335 battery instead. Or for this matter, any 3V lithium-based battery with three solder terminals with the required raster. Just like I did with the CR2450.

As a side note, one of the chassis rust spots is clearly visible on the right side of the battery.

For standard PC users (and builders), a mainboard with integrated RAM chips might sound outdated. At least, I think about the old IBM XT systems with those large array of onboard RAM chips. For those who have worked with similar computers from Dell, Packard Bell, IBM, and possibly others, having onboard RAM might be as expected. But for me, it's a curiosity. Why did they choose to go that way? It beats me. Probably for cost-cutting purposes so that they could sell PCs with 4 or 8 Mb of RAM without any SIMMs. Could be.

For the record, this mainboard has 4 Mb of soldered 70 ns RAM chips. And it came with an additional 4 Mb SIMM inserted in the first memory slot. Examining the upgrade path documentation, reveals that the maximum amount of RAM for this PC is 128 Mb, organized as 4 x 32 Mb SIMMs. In this configuration, the whole 4 Mb onboard memory chips are ignored.

Another curiosity is related to the amplified audio output. That is an interesting approach, but quite uncommon. I imagine you could use the software mixer to control the volume of the integrated sound card. But then again, a dedicated stereo speaker system with internal amplifier was a far better choice back in the '90s. Nowadays, I just pass everything through a (Sansui AU-8500) power amplifier and I either use my headphones or the big speakers.

By the way, even the PC Speaker is amplified. And I thought I invented (joking!) this idea for my 32-bit 80386DX ISA Single Board Microcomputer. When I first booted the PC, I received a painful PC Speaker beep, straight to my auditory cortex. The volume was so loud and with the top cover off, the beeping sounds were totally annoying. In addition, there is no hardware volume control.

I discovered later that the entire sound card output, including the Yamaha OPL-3, is routed to the PC Speaker. Basically, the audio output of the AD1848 codec is amplified and fed to the PC Speaker header. Without further analysis, I suspect the TDA7052 IC does the job. When I first saw the audio circuit section, I instantly thought about my ISA Audio Interface. Both share similarities, and I'm pretty sure the PC Speaker output signal is collected from AD1848 pin 47 (MOUT).

Since I wasn't able to find any DOS driver for the Compaq Business Audio sound system, I just wonder if it would work with a modified version of my AIF driver. If only I could find the datasheet for the controller chip that talks to the AD1848 codec...

Thankfully there is the WSSXLAT.EXE Sound Blaster emulation pogram for the Windows Sound System. It only works together with an expanded memory manager and provides good compatibility with some games. Unfortunately Doom is part of the exception list.

One last curiosity: some chips run very hot to the touch. The CPU has an undersized heat sink and boils everything around it. The video controller burns hot. Heck, even the RAMDAC runs very hot. Not to mention that one of the chipset ICs is also slowly cooking away. By the way, there's a small IC right next to the CPU socket; it nearly burned my finger.

I measured the power supply voltages and I got a steady +5.01 V and +11.90 V. Mainboard ICs run at 5 V, thus everything is within specs. It's time to add heat sinks.

Conclusions

To me, this PC is a contrast between quality components, overengineering, careless layout, and upgradeability, albeit with unobtanium parts. Don't get me wrong, it has its own charm. But sometimes, it's a pain to get along with it. Especially since it uses that floppy disk-based setup program. Well, you can shift everything to a hidden partition on the hard disk drive. But that's even weirder, and you still need a floppy disk for the first setup. I ended up copying the setup program and adjacent files to a directory on the hard disk drive. I can access it from there, whenever I need. Thus, as long as the hard disk is bootable, there's no need for a bootable floppy disk to run the setup program.

I guess these kinds of systems were IT infrastructure engineers' dreams. All identically configurable, predictable, easy to deploy, and easy to maintain -- if you knew the procedures, of course.

But hey, my dream finally came true and I have a chance to play with one of these Prolinea desktops. And I enjoyed every step of this restoration. Well, maybe the the cache and VRAM expansion boards set me off for a bit. But then again, it's not like I live in the mid-1990s and this is my only PC. As I said, I just have to adjust my expectations. This time, by lowering the stakes.

I connected the PC to a free channel on my KVM switch, and I played some old MS-DOS games, including Doom and Wolfenstein 3-D. The look and feel of this old desktop, combined with the floppy and hard disk drive sounds, give that nostalgic '90s feeling.

Interestingly enough, Doom runs smoothly. I guess that's due to that Motorola video controller.

Up until further upgrades, I will follow my initial plan of converting this machine to an HP-IB controller. But that would be the subject for another essay.

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