Solving the HP16500 Compact Flash card mystery

The HP16500 series of logic analyzers comes in three versions: the HP16500A which only runs from LIF formatted floppies and the HP16500B and HP16500C which also incorporate an IDE hard drive, can use MSDOS formatted floppies and where the HP16500C has the most powerful CPU, supports the most memory (mine runs with 64MB now) and has added networking capabilities out of the box.

By now all the original IDE drives are either failing after such a long time or they make rather strange sounds indicating that their end is rather near too. The immediate idea is to replace them with solid state storage, either in the form of an IDE SSD or using compact flash cards which have an electrical interface that is compatible to IDE/ATA.

IDE SSD are rare and/or expensive and you need to take into account that the HP16500B/C operating system only supports FAT12 or FAT16 formatted drives and is thus limited to a drive size of 2GB. 

So the easiest way to replace the aging spinning disks is to use a 40-pin IDE to CF adapter and a compact flash card. Sadly a quirk in the 16500 OS makes this not such an easy task.

Many users have found out that the 16500 are very picky about which CF cards actually work, some are rejected outright and the unit does not even boot, others can seemingly be formatted but then no files can be written to the cards. Some people assume it’s due to the specific brand of the IDE to CF adapter, others think that the 16500 issues some special IDE commands that certain cards don’t support. The real reason is much simpler and unfortunately makes finding a supported card a real game of trial and error.

Out of the whole IDE/ATA specification, the HP16500B/C only uses three commands, namely Read Sector (20h), Write Sector (30h) and Identify Drive (ECh). The Identify Drive command returns information about the drive parameters, like model name and serial number but most importantly the drive size and geometry. Amongst the data returned is also one field named “Number of unformatted bytes per sector” which has been present in the earliest versions of the ATA specifications that I could find but for which there was never given any explanation is to what it actually means. 

At the time the HP16500B/C were made all hard drives had a sector size of 512 bytes and this number is mentioned explicitly in the specifications several times, without referring to “Number of unformatted bytes per sector”. This field is present up to the official ATA-1 specification but was then quickly retired in the ATA-2 spec of 1996 marking it as “Vendor specific (obsolete)”

When the HP16500B came out in 1994, I assume all hard drives would report the “number of unformatted bytes per sector” as 512 and so the 16500 OS uses that number in order to format and operate the connected hard disk (or SSD or CF card)

Sadly old and current compact flash cards report all kinds of sector sizes. Out of the random collection of cards I acquired over the years or bought specifically in the past weeks, I have seen sizes of 512 (correct), 64, 528, 576 and even 0. For some cards I could find the data sheets and confirm these number there too.

The 16500 dutifully tries to create a FAT16 filesystem using the number as reported by the card but then fails to create a file. Only if the card reports a correct sector size of 512 the card will work.

I have also tried to outsmart the 16500 by using SD cards and an SD to CF adapter of which I have two, one bought in the early 2000s for which I can find no reference on the net and one acquired recently and which uses the common FC1307A chip inside. The early SD to CF adapter gives a sector size of 512 for all SD cards and works, the newer model sadly always reports 576 and thus cannot be used either.

here are all the cards and adapters I tried:

• old SD to CF adapter:
• 32 MB SD Sandisk: works
• 512 MB MMC extrememory: works
• 1 GB SD Sandisk: works
• 4 GB SD: not recognized by the adapter (2GB limit?)

• new SD to CF adapter: 
• reports 576, does not work with any SD card 

• 16 MB CF Canon: works
• 32 MB CF Unknown: works
• 64 MB CF HITACHI: works
• 64 MB CF extrememory: reports 0, unit does not boot
• 256 MB CF DANE-ELEC: reports 528, does not work
• 256 MB CF Sandisk: reports 576, does not work
• 512 MB CF Sandisk: reports 576, does not work
• 1 GB CF iCF4000 Innodisk (bought in 2025): reports 512, works!
• 1 GB CF MemoryPartner (AliExpress, 2025): reports 512, works!
• 2 GB CF MemoryPartner (AliExpress, 2025): reports 64, does not work
• 4 GB CF MemoryPartner (AliExpress, 2025): reports 512, but is larger than 2 GB so does not work

As the Innodisk iCF4000 has been reported to work by others before, is reasonably sized and seems to be easily available at the time of writing (July 2025), it’s the card I would recommend to get and use with the HP16500B/C. I got a few of them recently and paid ~$7 per card

https://www.eevblog.com/forum/testgear/solving-the-hp16500-compact-flash-card-mystery/

Converting a Soundcraft EPM8 to pre-main mix headphone and monitor out

This shows how to convert a Soundcraft EPM8 mixer to pre-main mix headphone and monitor out, which allows to use the headphones even if the main mix level is all the way down. Or send the monitor out to a second set of speakers independently of the main mix volume level.

The modification probably applies to the whole range of EPM6, EPM8, EPM12, EFX8 and EFX12 mixers, if in doubt check the service manuals. 

 

howto:

remove all knobs, fader caps, jack nuts,washers and top screws, remove screws on the sides, back and bottom (do not remove the screws on the mains power inlet and the ones next to it) 

desolder the two 10k SMD resistors R26 and R27:

solder the two 10k resistors next to C3 and C4:

wire bottom pad of former R26 to 10k next to C3 and bottom pad of former R27 to 10k resistor next to C4:

carefully reassemble in reverse order :)

Pressing the "2 Track to Monitor" button will now send the pre-fader main mix to the monitor and headphone outputs.

Euclidean Circles

it's a panel! it's a PCB! it's Euclidean Circles by av500!

more here: https://www.muffwiggler.com/forum/viewtopic.php?p=2077790

Skating on thin Samson-ice

One would think it sensible to make luggage wheels really robust, but apparently they are only good for the smooth flooring inside the airport. These Samsonite wheels started to disintegrate already after half a dozen trips and instead of trying to get equally bad ones as replacements I opted for sturdy roller hockey wheels, replacing both at the same time.

Mounting the new wheels meant drilling out the rivets in the original axles and drilling and tapping an M3 thread inside it so that they are now secured with a screw and a large washer. Not pictured is securing the two feet opposite the wheels with M4 screws instead of the tiny plastic standoffs that were starting to break as well.

le sigh.

Dynacord HiFi Favorit 2 Pot Mortem

After 10 years in storage, when I wanted to check the state of my Dynacord HiFi Favorit II amplifier, there was no sound coming out of it, so I got to work:

1) The mains and the anode voltage fuses checked out OK, but the internal preamp power supply (40V for the transistor section) was blown. Sacrificing one more fuse which also blew instantly meant something was drawing too much power. The power supply has three identical section, each with one BC147 transistor and one of these gave funny results when checked for the typical diode behaviour between the gates. I replaced it with a BC546B which I had at home and the power supply was back in business.

2) Still no sound except some hum from the speakers meant that the power amp section was probably working, but there was no signal coming from the preamp. Feeding an audio signal directly to the input of the master section revealed that there was no signal past the master volume potentiometer. Since getting a spare pot that fits exactly would not be so easy for this 40 year old part, I decided to try to fix the potentiometer first.

Taking it apart revealed that the metal spring ring that holds the carbon wiper was broken in two places and that somebody had already tried to repair it by adding a blob of solder across the break. But solder is soft and thus it bent and broke itself after some time:

Eventually declaring this pot a write-off (not true any more, see below) I looked into my spare parts for a suitable replacement. I found a somewhat similar 100k Log pot which had the general shape but a much longer threaded bushing and no D-shaft. Overall the shaft length and bushing diameter were the same, so I decided to shorten the bushing and convert the round shaft into a D-shaped one. I took the replacement pot apart and took the top casing and the shaft to the mill for a quick makeover:

3) With the volume pot replaced, I had a working master section again, so I turned towards the two input sections. Section I was working, but the sound was very muffled and the treble potentiometer did nothing, whereas the bass control was fine. Treble and bass are controlled by a dual concentric potentiometer with specially shaped 4 and 6mm shafts. In addition to the special shafts, this potentiometer also has an "S" type taper (see here for S taper) making finding a replacement almost impossible. So again, let's fix it. Opening it up, I saw that it had the same type of failure, the wiper ring of the rear section breaking at the exact same two places:

knowing I could not fix it permanently by just adding some solder, I decided to add a "brace" to the ring. At first I thought of using a piece of wire, but that would bend over time as well, so I picked a sewing needle which is from very stiff material and still easily solderable. I clipped two short pieces and soldered them across the break on the side of the ring where there was some clearance above:

Dry fitting the rear section, the wiper now had good contact across the whole rotation range. Although the front section was still working, I checked the ring as well and found that it was beginning to break as well, so I added the same bracing there too.

I also checked the volume potentiometer, but that one looked fine, so I left it as it was for now - and I do know how to repair it if needed. I can also go back and fix the volume potentiometer that I initially replaced, but that can wait a decade or two...

4) Section II had a volume pot that was broken in the same way, but the bass/treble pot was still good, so I had to repair only one wiper in the same way again:

5) the "Vibration" circuit, which is actually a "tremolo", and that works on the signal of section II was still working fine, so time to put it all back together and light it up:

https://plus.google.com/u/0/+VladimirPantelic/posts/2Sqf7ftsKhT

keeping a list of my modular synth DIY projects on muffwiggler

• my first completed Euro module - a powered speaker: https://www.muffwiggler.com/forum/viewtopic.php?t=140455 
  
• panel exposing Euro power connector: https://www.muffwiggler.com/forum/viewtopic.php?t=140623 
  
• the "probetiple" - hook your scope: https://www.muffwiggler.com/forum/viewtopic.php?t=141505 
  
  
  
• 8x8 (16x16) MIDI control true summing matrix mixer: https://www.muffwiggler.com/forum/viewtopic.php?t=138964 
  
• Behringer FX600 / Coolaudio V1000 effect module: https://www.muffwiggler.com/forum/viewtopic.php?t=145258 
  
• wood veneer panel and wooden pot knobs: https://www.muffwiggler.com/forum/viewtopic.php?t=145219 
  
• recycled PCB panel DIY ring modulator: https://www.muffwiggler.com/forum/viewtopic.php?p=1994520
  
• I/O - modular to line level (and back) converter: https://www.muffwiggler.com/forum/viewtopic.php?t=146459
  
• DIY 8 channel trigger to MIDI converter: https://www.muffwiggler.com/forum/viewtopic.php?t=146538
  
• 8 step clock divider/sequencer that rules! https://www.muffwiggler.com/forum/viewtopic.php?t=146845
  
• 0.5U DIY STM32 debug and distribution bus panel https://www.muffwiggler.com/forum/viewtopic.php?t=147407
  

• Euclidian Circles! https://www.muffwiggler.com/forum/viewtopic.php?p=2077790
  
  
  
  

Converting a Canon Extender FD 1.4 to EOS mount

The original Canon "lens converter FD-EOS" was only sold through Canon Professional Service and few were made, so used ones are hard to get and very expensive. It is said to be of very good optical quality, compared to the cheap 3rd party converters that are available now. In order to adapt from the 42mm register of the FD mount to the 44mm of the EOS mount, some optics are needed in the converter, so it also acts as a 1.26 teleconverter, losing 2/3 stops of light. It also protrudes inside the lens, so it can be used only with a few tele lenses.

Looking at the image of the original converter, I realized it looks very similar to a Canon 1.4 teleconverter, which also has this protruding element and can be used with only some larger teles:

  

Both converters have some optics and both of them add some "length" between the EOS mount and the FD lens, so I thought, why not make the length of the FD 1.4 match the EOS register and therefore make a 1.4 EOS-FD converter with good optics inside.

In order to get something that connects to the EOS mount, I bought a (cheap) M42-EOS adaptor. The adaptor is not totally flat on the front, so it was flattened first

After removing the back of the 1.4 extender, I measured how thick the "ring" that goes between the M42 and the converter front needs to be and finally settled on the magic value of 20.4 mm between the EOS and the FD mount (20.4 mm includes the front part of the 1.4FD and the M42)

The "ring" was made by a friend and connects to the 1.4 FD through the original screw holes. To attach the M42 3 new holes were drilled into the EOS flange of the M42. The little "stopper block" was added to push the "stop down lever" on the FD lens and therefore to allow to stop down the lens which would otherwise be fully open all the time. When mounting the lens, one has to rotate it slightly into the other direction to engage the stop down lever first, but this is easy to do and works fine. (UPDATE: the stopper block was a bit to short and therefore with some lenses the stop down lever "slipped" past it, it is now glued to the back of the 1.4 FD in the same position - works fine and still can be easily removed if needed)

 I wanted to leave the 1.4 FD unmodified, but the "tube" on the back side goes too far into the EOS mount and blocks the mirror on both my EOS600 and EOS33, so about 1.5 mm were taken of:

After assembly the new 1.4 FD-EOS converter is ready to be used:

 Now put on FD and EOS caps :-)

UPDATE: I got a new M42 to EOS adapter with "AF-Confirm", this is a little IC on the back of the mount that interfaces with the camera and pretends to it that a lens (with fixed aperture 2.0) is attached. This has two benefits: The camera will try to autofocus and will therefore enable the AF sensors. If you focus correctly the AF sensors will light up and confirm (hence the name) correct focus. Some EOS cameras do not measure exposure correctly when no AF lens is attached (like EOS5/EOS30, see here), with the "fake" lens stopped down metering is correct. These AF-Confirm adapter can be had (different mounts converted to EOS) from various eBay sellers, mine cost about $60. I just added the 3 holes to attach it to the "ring".

EOS 30/Elan 7E with FD 300/2.8 attached:

http://www.vp7.de/eosfd/eosfd.html