To make it clear from the beginning: this is a (possibly) destructive method of reading ROM chips. The process of extracting and possibly a resoldering of the memory chip might fail. In my case I’ve tested it on two Sharp CE-150 PCBs I’ve declared to be spare parts. It is only a proof of concept as there are simpler non-destructive ways of ROM extraction on a Sharp PC. I was just curious and so I’m describing my experiences.
Well… At first I did not want to desolder the ROMs: I started with the intention to use a set of probes attached to the individual pins of the chip to read the content of the Sharp PC / CE ROM chips. This did not work due to the narrow leg distance of the QFP chips (0.8 mm).
Desoldering QFP chips can be done rather quickly with a hot air gun. At least that’s the most comfortable way I know of. I usually add some flux and in some cases larger quantities of leaded solder. The latter decreases the melting point and speeds up the process. I don’t care about solder joints as the chips and the pads can easily be cleaned after the removal. Excessive amounts of solder can be removed with flux and a clean soldering iron tip.
This was a little test out of curiosity… I’m currently playing around with an amplifier circuit for the Sharp CE-150 audio output (CMT-OUT) and wanted to see if the signal I’m getting is already distorted when leaving my Sharp PC, or if my circuit and/or sound card is causing the distortions.
The CE-150 uses Frequency Shift Keying (FSK) to transfer binary data via audio signal (e.g. to a tape recorder). It sends four pulses of 1.27 kHz for a binary “0” and eight pulses of 2.54 kHz for a “1”.
To test the circuit I’ve taken the original design and simulated the circuit in LTspice (running under Linux with Wine). This tool allows the simulation of various analog (and digital) circuits – perfect for my test.
The result was – to be honest – pretty surprising for me. The upper screenshot shows the LTspice simulation of the output signal, the lower screenshot was taken from a WAV file in Audacity. I was not only able to simulate the circuit but also to use the resulting signals as a good approximation for my amplifier circuit (not shown). 🙂 One minor fix (also not shown) left was to adapt the transition time between a “0” and a “1” to better fit to the original curve.
In this post I’m describing a method which is widely used to Dump RAM and ROM images on Sharp PC-1500 and PC-1600 systems. This method is non-destructive and can be used on most Sharp PC ROMs and extension cards. It only requires a Sharp CE-150 extension, an audio cable, and a computer with a microphone input (i.e. sound card).
Besides a plotter, the CE-150 Color Graphic Printer also provides two audio interfaces (line-in and microphone output). These were (and still are) used to transfer code or data between Sharp PCs and tape recorders. Today, such recorders are mostly outdated but the method works nonetheless with sound cards. Software tools are freely available (e.g. pocket-tools) that allow the transformation of recorded audio files into binary dumps and even further into BASIC code.
To facilitate the access to Sharp Pocket Computer schematics I’ve started to collect and mirror some of them on my web site. This should allow Sharp PC 1500/1600 enthusiasts to update, modify, and especially to repair their hardware.
The Sharp PC 1500/1600 series are obsolete hardware. Their schematics are already freely available on the internet and therefore considered to be in the public domain. Please inform me if you own a copyright on some of this material and do not want it to be available on my web site.
It’s not that easy as it may sound to find paper rolls for a 30 years old printer, the Sharp CE-150. The printer is used in combination with a Sharp PC-1500/1500A pocket computer.
I’ve looked at my small amount of paper rolls, the leftovers I’ve found in a box on the attic. Interestingly they were differing in size (can’t remember why):
|(Left to Right)
Their width and outer diameters did not differ significantly, but the core diameters did. Paper rolls with core diameters of 7-9 mm are hard to get, the rolls sold today mostly have a diameter of 12 mm. I’ve successfully tested thermal (yes: thermal) paper rolls with this diameter in the CE-150, and these are really cheap to get (e.g. on eBay Germany). The ink doesn’t run, but there might be paper rolls with different coatings. I did not check that.
Maybe as a warning: Thermal papers mostly contain Bisphenol A (BPA), a substance that exhibits hormone-like properties!
The approximate dimensions you should look for are:
Width: 57 mm; Inner / outer diameter: 12 / 30 mm; Length: 10 m
One weakness of the Sharp CE-150 printer unit is the non-removal Ni-Cd batteries. After 20 – 30 years now since their release they begin to leak. The battery acid (potassium hydroxide, a base, actually) will sooner or later destroy the circuit board and anything else inside the printer. At that point the batteries are usually already dead and connecting a Sharp PC leads to “Error 78”, “Error 80”, or “Check 6″…
In case of such damages I usually use vinegar to clean up the case. Just put the case and any corroded parts (even if they are metallic) into a vinegar-water-mixture for a few minutes.
In case of circuit boards I’m using simple tap water and a brush to carefully remove the corrosion. Most parts on such a board can handle such a treatment. In this case I avoided getting water onto the relays and the ribbon cable. Afterwards drying the board is important, a regular hair dryer (or a temperature controlled hot air gun) will do.
I’ve made a short video tutorial on how to open, check, and if necessary repair a Sharp CE-150 printer unit which is used in combination with Sharp PC-1500 / PC-1500A / PC-1600 pocket computers:
One final remark: the printer will run fine even without the batteries. These batteries were used to provide the 1 – 1.4 A peak current to drive the printer solenoid and motors. The old power supply that was shipped with the CE-150 only provides about 500 mA. You can attach a newer one that is able to provide sufficient current without problems (9 V, negative pole is in the center).