Savel brain dump in English!

To start old Optrex DMC50264N LCD module you need to get +24V LCD bias voltage? Where to get it if you have only low voltage 3 … 5V? As LCD module drains very low current, it is possible to build very small DC/DC converter. There are lots of chips designed for this. I used MC34063, as I already had few of them in some old trash boards. The schematics are typical, used from datasheet. As the current is very low, it is possible to use very small SMD inductance. I didn’t find very small, so I used quite big- about 1cm tall…

Schematics for printing

Components used in my testing board: C1- unknown, C2- 330µF x 10V, C3- 10µF x 35V, R1- 1 Ω, R2 and R3- trimmer, R4- 180 Ω, L1- unknown, D1- some smd S36K…

PCB board for printing in pdf format.

When the voltage and LCD contrast is regulated, just measure the resistance of trimmer and use the values in R2 and R3. As MC34063 is quite powerfull chip: 3V to 30V Input Voltage Operation and internal 1.6A Peak Current Switch, the output current can be increased- just use proper coil and diode. Also use proper cooling for whole device. But remember that SO device can handle only 625mW (DIP- 1W).

One of the popular programs for PCB tracing and circuit diagram drawing is Eagle from Cadsoft. The software is available for Windows, Linux and Mac operating systems.

Freeware version of software has some limitations: The usable board area is limited to 100 x 80 mm (4 x 3.2 inches), only two signal layers can be used (Top and Bottom) and the schematic editor can only create one sheet.

But such limitations are not very bad for novice and amateur users. You can download the software from site at: http://www.cadsoft.de/ .

The component base are quite big. There is user exchange ftp in the site. And it is very easy to create new element by yourself.

The bad sides of the program: autoroute functions is very dumb. No autoplace function. And one problem with pads and holes. Some elements have very small pads and I can’t increase the size without editing library.

Got some bad security video cameras for recycling. Few color ones made by Philips, two Sanyo and others KC-263C and KC-383C. It is mid and high resolution black and white CCIR video cameras.

Security cameras’ bodies and some generic brown Pokemon.

The KC263 and KC383 are powered from the mains power. It can handle 85…265V AC. And the problem in these cameras is that power supply is very ugly made. The problem is with 12V output capacitor. It is 1000µF x 16V low ESR capacitor. Manufacturer used cheap product and all the caps were blowed up like in computer main board. As voltage is only 12V, I decided to use capacitors from mainboards. I needed to drill extra hole and use much bigger cap. But now I can use 1000 or even 2000µF caps x 16V.

Even camera with missing PSU is repaired. I is working from my computer PSU.

About color philips cameras (LTC 0450/51). The problem is same. But as power supply is much more complicated, I need to replace 9 capacitors: 8 @ 10µF x 35V and one 220µF x 6.3V. Small caps replaced with exact ones, big was replaced with 1500µF x 10V from computer motherboard and made by Sanyo. Both color cameras are working…

Also there are two cameras from Sanyo. They are powered from external 12V PSU. One camera is dead (internal converter), other is working.

Connect pulse generator from older post to your audio amplifier. Set volume to something in the middle. Connect oscilloscope to the output of the amp with dummy load.

You will not see ideal square signal in the output, but all these distortions can describe your audio amplifier.

As there are lots of images in this post and big table. So press on the link to read more about audio amp tuning…
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For further audio amp analyze we need square waveform generator. I can use my generator, but we can build one using very common TTL chips. We can use any 74XXXX chip which can be combined to “NOT” logic element. Most common chip is 74LS00. In my breadboard I used 74LS04… I used all idle “NOT” elements to buffer signal.

When powered, this schematics generate square form signal. Now, some theory:

In the right, red picture is undistorted square pulse. There are three main parameters: Umax, T and ti. Umax is amplitude of the signal. T is – time, the length of waveform. You can calculate frequency (in Hz) from this: f=1/T. (if you measure in ms, don’t add all zeroes, just add k to the result. Same when using μs- the result will be in MHz).
ti -pulse length time. Another useful parameter is pulse duration ratio T/ti. In red picture it is equal to 3.

This is theoretical waveform. The real waveform (a bit artificially distorted) looks like in green image. There are additional parameters: tf and td. tf – leading edge time (pulse front), td – trailing edge time (pulse decay).

Umax is measured without taking any attention to all small spikes. ti is typically measured at 0.5 Umax (sometimes 0.7).

From Радио №9, 1989.

How to measure real output power of audio amplifier. Sometimes on some cheap audio devices you can see magical numbers like 1000W or something, and device is handheld. It is not real power, it is bullshit.

Attach dummy load to audio amplifier load. The resistance of the load must be equal to resistance of your speaker. Power dissipation of your resistor must be equal to your guessed audio amp power. Set your tone generator to sine wave and frequency to about 1000Hz. Connect oscilloscope to your load. And turn your audio amplifier and audio generator volume up until you’ll see distortion in the picture.

And now time for some math.

P=(U/2.82)²/R

In this example: R=4Ω, U=6V. P=1.132W

This was the power of my second tube amplifier. Audio amplifier is not fine tuned.

I removed few Optrex DMC50264N LCD modules with few buttons from some old laser printers. These modules are controlled by Mitsubishi M50530-026FP and M50521FP chipset. It is 4 lines 16 symbol special LCD module controlled by master CPU only by three wires. It is very simple serial to parallel converter made with the help of 74HC164A chip. All buttons are controlled in similar way using 74HC166A.

Pin out of J1 connector: 1- EXE, 2- +5V, 3- FPD, 4- GND, 5- CLCK, 6- GND, 7- FPS, 8- +24V.
For LCD control are used: GND, +5V, +24V (LCD contrast, can vary from 10…24V), CLCK, FPD, EXE.

Power lines are self explanatory. FPD is data stored in serial shift register and clocked by CLCK. EXE is connected to LCD controller and is used to strobe command from shift register. LCD controller can be controlled using 8+3 bits or 4+3 bits. This controller is connected in 4+3 way, so, programmer must send in the first SF command, that he will use 4 bit interface.

Data is shifted from MSB to LSB. Bits are in such order: (MSB) nc nc oc1 oc2 d7 d6 d5 d4 (LSB). For reverse engineering I wrote small program in MS Visual Basic and connected LCD module to LPT port using some TTL buffers (LCD module drains quite big load from data lines. Also, it drains quite high current from power supply- I used small ROHM BP5311 5V->24V DC/DC converter from same 5V power line).

The software is quite simple. The data is stored in windows in binary way. Selected rows are sent in serial way. Connections: LPT D3(pin 5)=DATA-FPD, D4(pin 6)=CLCK, D2(pin 4)=EXE

And here is the result:

Data from the buttons are read in same way. One, untested, note- I didn’t noticed any RESET circuit. So user must count any bit.

Most important is the firs byte sent to LCD controller. I decided, that it must be &H0D0B, (&HDB). It is SF command: I/o=4bit, Font=8, Duty=10, RAM=11 (4 lines x 40 words). As only first 16 symbols are visible, programmer must add 24 dummy symbols.

In older post I wrote that long time ago I built my first tube amp. Today, in old magazine, I found the schematics. As I remember, the output stage was working, but I made some mistakes in pre-amp. I left amp for very long time and my mother decided that it was junk and threw it away.

Big schematics for printing.

Recommendations for sound quality improvement: remove C9, C10 and C11. Change R2 to 240K, add feedback from output via 10K (R16) to Л1б cathode (dashed line in the circuit diagram).

Output transformer: Ш form core. Size of the core is about 4cm². Primary 2500 turns ПЭЛ 0.16 mm wire, secondary- 75 turns of ПЭЛ 0.8-0.9 mm wire. Output power ~3W, output resistance 4.5-5 Ω.

Tubes: Л1 – 6Н2П, 12AX7; Л2- 6П1П (miniature analog of 6П6С = 6V6!, maybe 6AQ5?)

Schematics from Радио 8, 1967.

For my audio amps I needed some small generator just for testing. And I also had MAX038 chip sample. Here is the abstract from datasheet:

The MAX038 is a high-frequency, precision function generator producing accurate, high-frequency triangle, sawtooth, sine, square, and pulse waveforms with a minimum of external components. The output frequency can be controlled over a frequency range of 0.1Hz to 20MHz by an internal 2.5V bandgap voltage reference and an external resistor and capacitor. The duty cycle can be varied over a wide range by applying a ±2.3V control signal, facilitating pulse-width modulation and the generation of sawtooth waveforms.

Frequency modulation and frequency sweeping are achieved in the same way. The duty cycle and frequency controls are independent.
Sine, square, or triangle waveforms can be selected at the output by setting the appropriate code at two TTL-compatible select pins. The output signal for all waveforms is a 2VP-P signal that is symmetrical around ground. The low-impedance output can drive up to ±20mA.

Schematics for printing.

Component placement:

Component values are described in MAX datasheet.

PCB image for printing in PDF format.

In German (sprut.de) pages I found small schematics for caps meter. This schematic is designed for electrolytic capacitor metering. According to author, device range is from ~10µF to ~65 500 µF. This is not very accurate meter, but it is suitable for testing big electrolytic capacitors used in computer mainboard. And you must remember, that all electrolytic caps capacitance is printed on the body of cap with tolerance of 10, 20%. And for very big one even up to -20% … +50%.!!!

I made it on my testing breadboard for testing. The rainbow wire going outside board is ICSP connector to Willem programmer.

The circuit is very simple. The MCU is Microchip PIC16LF876A-I/SP (I used this) or PIC16F876A.

Big schematics for printing.

ICSP connector must be connected to: DATA-RB7(pin 28), CLCK-RB6(pin 27), Vpp-MCLR(pin 1), Vcc-Vdd(pin 20), GND-GND(pins 8&19).

Warning! Capacitor must be discharged before connecting it to meter.