tkc8800

Technology and retro computer blog

Compaq Portable II new video and sound card

I recently received the replacement video board for my Compaq Portable II and I'm glad to say it worked perfectly.  See my previous post about the CPII here.  The board is Assy. No. 000525 which is a later board than what was in the machine, but it's an appropriate board for the Portable II.  There's much fewer components on this board and many of the components are surface mounted. It's great to have the internal CRT working again.


Working internal CRT
Working internal CRT
VDU Assy no 000525
VDU Assy no 000525

The Compaq Portable II is great for running CGA games, so I decided to get a sound card for it.  I managed to get hold of a Sound Blaster Vibra 16 CT4180.   This is the cheaper plug and play version of the Sound Blaster range, but it worked out well.  These cards also have a game port connector for connecting a 15 pin joystick, so needless to say I've got one of those coming as well.

I purchased the Vibra 16 not really knowing whether it would work on a 286 machine.  It’s a 16 bit board and I’ve got a spare 16 bit slot in the CPII, so I figured I'd work it out once it arrived.  Getting the sound card working in DOS took a bit of effort but I got it working.  The Vibra 16 is a PNP card designed for later machines than a 286.  So at first when I tried to install the drivers the card wasn't detected and running the Sound Blaster configuration manager would lock up the machine.


creative vibra 16 ct4180
SB Vibra 16 CT4180
creative vibra 16 ct4180 connectors
Vibra 16 ports
Compaq Portable II cards
Video & sound cards installed

In doing some research on the web I discovered a utility called EMU386 which is a driver that will emulate 386 opcodes on a 286.  The Vibra 16 software must use some 386 opcodes and therefore requires EMU386 to install properly. Once Emu386 was installed, I then installed the Sound Blaster basic drivers and the Sound Blaster Configuration Manager.  These two installs made all the necessary changes to the autoexec.bat and config.sys files and once I restarted the sound card worked.


Vibra16 sound card detected
Sound card detected
Compq Portable II ports
CPII card ports

While I was at it, I also installed MSDOS 6.22.  This took a bit of effort because I don’t have a 1.44 floppy connected to the machine, it only has the 360k floppy drive.  I didn’t like the prospect of creating 360k install disks for DOS 6.22, so I looked for another solution.  I’ve got a DOS 6.22 360k boot disk, so I used that to format the hard drive with the system files:

A:>format /s/q

This does a quick format of the hard drive and installs the system files required for a hard drive boot. Once that was done I simply removed the CF hard drive and connected it to my Windows pc.  I then manually created the DOS folder and copied the DOS files from my PC.

Here’s a video of the Compaq Portable II with Sound Blaster Vibra 16 running Prince of Persia, the sound is really impressive.





Downloads

See below for EMU386, Sound Bster Vibra 16 DOS drivers and the DOS 6.22 CD image.

DOS6.22_CD.iso.zip (1.79 mb)

EMU386_em3134b1.zip (18.15 kb)

sbbasic.zip (1.15 mb)

ctcmbbs.zip (671.25 kb)


Macintosh Sony SuperDrive head spring repair

I recently obtained a couple of compact Macs with Sony SuperDrives.  In both cases the drives wouldn't read disks.  I did the usual servicing of the insert/eject mechanism and both inserted and ejected disks fine, but they still wouldn't read disks.  In both cases the issue with the drives was that the top head was not touching the disk.  I managed to diagnose this by connecting the drive to the computer with the cover off and watching as it tried to read the disk.  Then I simply pressed down on the head with my finger so it would touch the disk.  Once I did that the drive would start to read and write.


This seems to be a common problem with these drives because they use a leaf type spring on the top head.  What typically happens is when the machine is stored away for years on end with no disk inserted, the drive head is held in the open position and this causes the head to stay in this raised position.  The other cause would no doubt be people unwittingly raising the head too far in order to clean between the heads.  This would cause the leaf type spring to bend upwards.


I'm glad to say I've found a fairly easy fix to this problem.  I've repaired both drives and they are now working fine.  So I thought I'd write a guide on how to fix this head spring problem.  The fix involves two things:

 

  1. Bending the leaf spring on the top head back down
  2. Adjusting the internal spring inside the head to further drag the top head down on the disk.

 

In order to perform these tasks you need to remove the head from the drive.  This is a fairly simple process.  There are two small screws holding the head down.  These screws clamp down the slide bar on the right side of the head (looking from the back of the drive).  Then there are two small card cables which simply pull out of their sockets.  These need to be removed.  Once both those things are done the head can be removed from the drive.

To bend the leaf spring back down again, you need to insert a small flat head screw driver towards the back of the head assembly.  There is a small metal plate where you can rest the screw driver.

Sony SuperDrive

 

Push it in enough to spread the heads apart.  Once that's done you push down gently on the top head.  The screwdriver acts as a fulcrum forcing the spring to be bent back down.


Sony SuperDrive

 

The second fix involves moving the position of the small spring inside the head to increase the tension on the top head.  On the bottom of the head assembly there are three small adjustment steps that enable you to increase the tension on the spring.  But I've found that even moving the head to the third position is not enough to provide enough downward pressure on the top head.  So my solution was to notch out a fourth position further away.  I used a broken off piece of hacksaw blade to create the new notch.  This increases the tension on the spring enough to provide the required down force.

Sony SuperDrive

 

Internal spring moved to the fourth position.

Sony SuperDrive

 

Macintosh LC575 disassembly for donor parts

I've been looking for a hard drive and floppy drive for my SE/30 restoration, so as luck would have it I found this LC575.  I offered the owner $20 which was accepted.  I hoped to get the hard drive and floppy out of it as both would make nice era appropriate replacements for the drives in the SE/30.  I'm glad to say both worked out well.  I managed to salvage a 250meg Apple SCSI hard drive and floppy super-drive from this machine, both work, but in need of a clean-up, as would be expected.  I also managed to remove the internal cd-rom drive.  I haven't tested that yet but no reason to expect it won't work.  Before tearing this machine apart I did try to get it to boot, but on power up all I could hear was the dong of the screen.  The screen was just blank and no activity from the hard drive or floppy could be heard.  The only attempts I made to get it working was to check the fuse on the power board, that was ok.  I also tried the trick of switching it on and off really quickly, I'd learned this trick when trying to get my LC475 working.  If the clock battery is dead the LC475 won't start up, but switching it on/off quickly will get it to boot.  But no luck with the LC575.  Not wanting to spend too much time trying to get the thing working I just started tearing it apart.  I must admit it's quite good fun to disassemble stuff.

These aren't too hard to take apart, a few Torx T15 screws on the back and the back just lifts off.  The floppy and cd-rom drives can be removed through a drop-down cover at the front, no screws required.  The hard drive and logic board come out through a cover on the back which does have a couple of screws but were missing from this one.  The internal drive/board case just un-clips from the front bezel and can be removed.  A fairly interesting case design.  Case parts and monitor will probably go to recycling.  The logic board looks in fairly good shape and has the ram and CPU on it which are most likely good, so I'll hang on to that in case someone wants it.  See pics below.

 


An adapter for replacing 2708 eproms with 2716 eproms

2708 eproms were used in early computer equipment and arcade machines, but unlike more modern eproms they require a triple voltage for programming.  Because of this odd voltage requirement many current eprom programmers don't support them.   2716 eproms are later model eproms which have a very close pin configuration to the 2708's, but are supported by many current eprom programmers.  A simple three pin modification can be made to the 2716's to make them usable as 2708's.  2716's have a 2k capacity, as opposed to 2708's which are 1k, so you only use half of the capacity, but as they are readily available and fairly cheap, this is not a big issue.  2816 electronically erasable eeproms can also be used instead of 2716's.  The 2816's are pin compatible with 2716's but are electronically erasable rather than UV erasable, so they are even easier to work with.

 

To avoid making changes to the original 2708 equipment and the 2716 chips, a 24 pin socket adapter can be made to fit between the original 2708 socket and the 2716 chip.  This allows the 2716 to be programmed on a modern programmer and then placed into the adapter socket for use as a 2708.  To create the adapter, I use two 24 pin sockets, the upper socket contains the wire connections and the lower socket has pins 18,19 and 21 removed.  See pictures below.

 

To create the adapter, the following connections need to be made in the upper socket:

 

  • Connect pin 21 to pin 24
  • Connect pin 18 to pin 20
  • Connect pin 19 to pin 12  *

 

* Pin 19 is connected to pin 12 which uses the first 1k in the 2716.  Alternatively pin 19 can be connected to pin 24 to use the second 1k in the 2716.

 

Then in the lower socket pins 18, 19 and 21 need to be removed.  See pictures below.

 


Bottom view of upper socket, bottom far left pin is pin 12, top far right pin is pin 24

 

 


Completed adapter showing bottom socket with pins 18, 19 and 21 (left to right), removed

 

 

 
Top view of socket adapter, top far right pin is pin 1, bottom far right pin is pin 24

 

 


This diagram shows the pin assignments for both the 2708 and 2716 and the required wiring connections and pin removals to enable the 2716's to be used in place of 2708's

 

 

 Click on image for larger version
 
Here are the adapters in use in an eprom card installed in the Altair8800.  The Cromemco 8k Bytesaver card has capacity for eight 2708 eproms.  2816 Xicor eeproms have been used in all eight slots using the adapters.  Chip zero (far right), contains a 1k rom monitor program and chips 1 to 7 contain MITS 8K Basic.  Using the monitor program 8k Basic can be transferred into ram almost instantly with a simple command from the terminal.

 

 

 

 

 

Serial cable file transfer, pc to Macintosh 128k/512k

Getting software onto floppy disks for old Macintosh computers, such as the original 128k and 512k can be difficult.  The problem is the floppy disk standard they used is no longer supported on any modern machine.  These early Macs used standard double density 3.5" disks, but they were formatted with a 400k and later 800k floppy format.  This standard is no longer used by modern computers.  The old Macs are also difficult to connect to networks, especially pre-SCSI Macs like the 128k and 512k machines.  They had serial ports but a problem with serial transfer is that they used the RS422 standard, not the widely used RS232 standard that most computers, like the Apple II, use.

 

Many enthusiasts of these old Macs use a bridge computer to transfer software to disk.  There were several Macintosh computers produced during the late 1980's and 1990's that supported both the old 400k and 800k formats and also the more widely used PC, 1.44mb high density format.  The drive in these machines is called the Superdrive.  Some models that have the Superdrive are the Macintosh SE/FDHD, the SE/30 and the Powerbook 520c and 540c laptops.  There are also others.  A bridge machine offers a great solution especially if that machine has ethernet capabilities.  While a bridge machine is great, if you don't have one, the simple solution is to use a serial cable.

 

USB to serial adapter cables are cheap and readily available and they will add a serial port to your modern computer, but they are wired for RS232 standard serial communications not RS422 like the old Macs.  The solution is to create an RS422 to RS232 adapter cable.  Then you simply connect this cable between the Mac and the USB to serial cable.  See description below for how to create this cable.

 

Another issue with old Macintosh computers is that they're unusable without a boot disk.  Unlike the Apple II which has inbuilt Basic in ROM.  So unfortunately if you purchase one without any disks you can't create the disk to use it, like you can with the Apple II using something like ADT Pro.  You need to get your hands on a bootable 400k floppy disk.  What's more to transfer software to the old Mac via serial you need a couple of important utilities on that boot disk.  The required software is described below.

 

Macterminal transfer
Xmodem transfer from Windows 7 pc running TeraTerm to Mac 512k running MacTerminal 1.1

 

Creating the serial cable

The following table shows the pin assignment of the Mac 128k/512k de-9 serial connector (RS422 standard).  The second table shows the 5 pin adapter cable required to convert RS422 to RS232.

 

Macintosh 128k/512k RS422 serial connector
Pin Description
1 gnd
2 +5v
3 SG
4 TxD+
5 TxD-
6 +12v(HSKo)
7 HSK1(DSR)
8 RxD+
9 RxD-

 

The table below describes the connections required to create an RS422 to RS232 adapter cable.  The connector at the back of the Mac 128k/512k is a de-9 female connector.  And the connector on most USB to serial adapters is usually a de-9 male connector.  Therefore the cable below has a male de-9 connector at the Mac end and a female de-9 connector at the other end.

 

Macintosh 128k/512k RS422 to RS232 serial adapter cable
Mac de-9 Male PC RS232 de-9 Female PC Signal Name
7 7 CTS
6 8 RTS
9 3 TXD
1 5 GND
5 2 RXD

 

 

Required software

In order to transfer files to the Mac, you need a few utilities: MacTerminal 1.1, BixHex 5 and/or Packit 1.0.  The terminal program is required to do the file transfer and BinHex or Packit is required to preserve the resource fork on the old Macintosh files. BinHex 5 will only archive a single file, whereas Packit allows you to put multiple files into an archive.  But the great thing about these utilities is that both will open any file once transferred, they don't rely on the file type.  The following table shows the software on a 400k boot disk that will allow you to boot the  Mac and do file transfers.  Even with all required software this disk still has around 180k free, so you can transfer files directly to it.  The system components for this disk have been stripped right down of unnecessary fonts and desk accessories to maximize free space on the disk.

 

Macintosh 400k boot disk for serial transfers
Utility size
System 2.0 50k
Finder 4.1 47K
MacTerminal 1.1 98k
BixHex 5 8k
Packit 1.0 9k

 

Download the disk image for this disk here: MacTerminal_Binhex5_BOOT.zip (176.29 kb)

 

 


By booting an old Mac with this disk, you can transfer files in a BixHex or Packit archive across the serial link using XModem in MacTerminal.  If the files will fit, you can transfer them directly to the boot disk.  If the files are too large for the boot disk, MacTerminal allows you to eject the boot disk prior to receiving a file, so you can write the receive file to a blank disk.  This gives you the ability to transfer larger files.  This process is made much easier if you have and external floppy drive, as you can extract the archived files to the external drive.  If you have a single drive you can still do it but you the process will require disk swaps.

This is a complete solution for transferring files from an internet computer directly to a Mac 128k/512k, without using a bridge machine.

See also my Macintosh 128k/512k disk image archive