In this post I will write some hopefully useful observations from working with the Compaq Presario CDS 520, with the goal of turning it into a MS DOS gaming machine, similar to my Presario 433 I owned as a child.
(This post is updated on a regular basis).
Compaq Presario CDS 520 specifications
- Year: 1994
- CPU: Intel 486 SX2 66 MHz (upgraded to an Intel DX2 66MHz)
- 8 mb ram (upgraded to = 20 mb (max = 64), through 2x8mb + 4mb on board)
- Cirrus Logic 512 kb graphics adapter
- ESS 688 onboard sound (upgraded to a Soundblaster 16, see below)
- ~500 mb hdd (upgraded to a 2gb compact flash card, see below)
- 3.5¨ 1.44 mb floppy
- Internal modem
- MS DOS 6 + Windows 3.1 default (now: MS DOS 6.22)
- BIOS: As explained by oldcomputer.info, these machines does not come with a vast range of configuration options in their BIOS. They autodetect your disks, and can boot from floppy and hdd. Larger drives than 540 mb can be used, although the limit is unclear (2.5 gb confirmed ok). To access BIOS, press F10 when the white rectangle is flashing to the right top of the screen during boot-up. If this fails, you do not have a setup partition on your computer. Then, you need to boot up from a floppy disk to access the bios. To prepare a floppy you need to download the SP1363.exe SoftPaq (see oldcomputer.info above, I will also provide links here shortly) and make a disk out of it. If you are making a clean install of DOS, you can also use this disk to make a setup partition on the hdd.
- Integrated builds. One limitation with these all-in-one machines is of course that if something fails, the whole machine might be rendered useless. They also have limited room for additional cards and other upgrades. That is essentially the cost of the compact form factor. My Compaq Presario 433 did not have an integrated CD-rom for example. Due to the slow LPT-port, the performance of parallel port CD-roms were limited, so I used long IDE- and Y-power cables and simply positioned the CD-rom outside of the machine. The advantage with the CDS520 is that it comes with an integrated CD, which is really beneficial when installing games etc. I still keep a lot of CDr’s at home for my Dreamcast, and other consoles.
Installing a Soundblaster 16
My biggest problem with this machine is the ESS688 onboard sound. Although it is soundblaster compatible in games, the sound volume tends to be to loud, and the front volume control does not do a great job adjusting it (neither did the software mixer). So, what I wanted to do first, was to install a faithful soundblaster 16 ISA card while still being able to utilize the internal speakers, and being able to accurately control the volume.
I found a soundblaster 16 CT2960 card on Austrian eBay for a good price. Although reading negative remarks about the VIBRA16-series I am perfectly fine with its performance. To use the internal speakers with this card, I connected them to the 3.5 mm out jack of the soundblaster, with a volume control on the audio cable coming out from the back of the computer. It works very well! Only problem is that the right speaker also served as the internal PC speaker. I solved this by simply using a speaker from a broken Nintendo Gameboy as PC speaker. This speaker had a most pleasant tone to it than the original. So, now I can enjoy games at a pleasant and adjustable volume, with full soundblaster compability. The installation is fully reversable and no harm was done to the machine.
The VIBRA16 driver installation was done by using the Sound Blaster 16 Value PnP (Vibra16) CD from Vogonsdrivers.com. Since the card is Plug n Play, it installs a TSR program, followed by additional configurations, such as the set blaster environment. Although these take up some memory it was not that bad (616kb of conventional memory left at the moment), they can probably be optimized later (I removed the content the installation added to config.sys).
Update: PC speaker and harddrive
I experienced two problems with the Presario lately:
- The harddrive started to act up (dying).
- The PC speaker went almost silent
Now, the harddrive was the easy part: I simply replaced it with a Compact Flash to IDE adapter, which enables the use of CF-cards as solid state hard drives. I was expecting to have to perform this upgrade sooner or later. I initiated the card and installed MS DOS 6.22 + added a bunch of games and Compaq files on it via the instructions on this site. I can really recommend having a virtual machine or two using VirtualBox or similar software. Very handy! This CF card had a boot delay of about 1 minute for some reason, but I switching to another CF card fixed that problem.
The PC speaker was more tricky. I tried to look for some sort of mixer or BIOS setting, but I have not heard about any such way of controlling the sound. I also tried with different speakers, without any improvement: the sound was just barely noticeable. Unacceptable on a DOS gaming machine! I figured the system board on the Compaq failed to deliver enough voltage to the speaker. So I went digging inside the chassi… There is a board that contains IDE, floppy and speaker connectors, which is firmly seated with four screws in the heart of the integrated build of the Presario. Perhaps replacing a few caps could help? After removing the board, I replaced three of them. Without any improvement. Speaker still silent 🙁
Finally, I found what was wrong with the sound: the TDA7053 amplifier chip! I order a new chip from Italian eBay, but it would not work since it was a TDA7053A (with volume control). However, I ordered a regular TDA7053 chip from China and that, together with a repair of a broken trace, fixed the problem!
I am far from an expert on electronics, but I found a way that works to repair broken traces for me. I put some self-adhesive copper tape between the spots that are to be connected, and then add flux and solder on top of the tape. Not always pretty, but it works.
The 486 SX/SX2 series cpu is rather slow compared to later models, such as the 486 DX2 66 MHz (which seems to be a bit of a flagship for retrogaming, based on eBay prices). The original cpu in the Presario CDS 520 lacks a coprocessor for example. First I upgraded the CPU to an Intel Overdrive 486 DX4 75 MHz I found cheap on Swedish eBay, but later decided to go for a DX2 66 MHz with the 33 MHz bus. I also benchmarked both these CPU:s as shown in image below. The DX4’s performance in Quake is slightly higher, but it shows some odd readings in Norton System Information.
CMOS battery replacement
The CMOS battery ended up dying on me. It is just a button cell battery so it won’t leak, but it is quite firmly attached to the motherboard. To replace it, I snipped and desoldered the connectors, and added a battery holder as seen below. Next time I do some work on the computer I will probably replace it with a horizontal holder, but this fix will do for now. I also replaced two capacitors on the mainboard (100uF, 25V) just because.