Savel brain dump in English!

First of all examine APC (American Power Conversion) LAN surge protector. It is removed from some APC UPS.

The circuit is very simple. Diodes D1-D4 and D6-D9 are IN4006. The D5 diode is more interesting. It is 1.5KE6.8CA. This is special diode: 1500 WATT PEAK POWER TRANSIENT VOLTAGE SUPPRESSOR.

Note J3. On PCB it is small gap between GND and signal wire.

In older telephone equipment special discharge devices are used for surge protection.

These devices are simple gas discharge tubes which can handle very high current for a short time. There single line protectors and protectors for symmetrical lines. We can use any of them in LAN protection.

One note to schematics. One side of line is directly grounded. In some cases, cable grounding must be done using some discharge device. Especially if the cable can be grounded in both sides. This will stop residual current in the cable.

Note: Grounding must be real! It must be real earth connection.

Here you can see discharge in the bulb:

BTW, high voltage generated by welder ignitor. P-27 gas discharger specifications: ignition voltage 310…390V, Resistance 5*10³ Mega ohms, max pulse current 2000A, constant current 2A, max pulse width 50…60μs, max frequency of pulses 50Hz.

5KP58: 5000W Transient voltage suppressor, (58V, 400A)
1N5908: Unidirectional diode, peak pulse power 1500W (10/1000mks), reverse stand off voltage 5V. The 1N5908 and SM5908 are dedicated to the 5 V logic circuit protection (TTL and CMOS technologies). Their low clamping voltage at high current level guarantees excellent protection for sensitive components.
BR211-140: Breakover diodes. Breakover voltage 140V, pulse 40A. A range of bidirectional, breakover diodes in a two terminal envelope.Typical application is transient overvoltage protection in telecommunications equipment.

If you want to build DVD/MP3/DivX/Xvid and etc. player you need only to design box. Take cheap power supply for +-12, 5 and 3.3V any DVD reading hardware and simple mainboard based on MTK1389 chip. Order MediaTek firmware and enter your logo… That’s all. This how this VIDO D403 DIVX player was made. The mainboard has silkscreen: MTK1389 DVD KHM280/310/HD60 rev.1.0 2004.05.18

As passed one year after I bought it and there is no warranty I decided to get rid of annoying high pitch noise in audio channel. Also OSD graphics was a bit distorted. I though that it is some power supply problems. I opened the case and made very small modifications. Replaced 1000μF x 10V capacitor with 3300μF x 6.3V one on 5V power line. Also increased cap on 12V line. Also added small (47μ and 10μ tantalum caps on same power lines). Also, I have big collection of mountable feritte core beads. So I placed as many as I could on the power lines.

The noice on audio lines decreased about 50% and on screen display is quite good. Only one notice- 3300μF cap is getting warm. This means, that power supply is still overloaded. I thing this PSU is too weak for this device- 5V is 4.9V, 12V is 11V.

For drilling wide holes in thin sheet metal I bought Irwin Unibit drill bit. It is self-starting drill.

For testing purposes I used steel sheet from ATX power supply box. Starting hole is a bit angular, next sizes are quite good. Only need to adjust the speed of the drill- to cut the steel, not grind.

In previous circuit, the temperature turn on the fan instantly. The regulation period is very short. To make it more wide just add only one resistor (R5):

While adjusting sensitivity of your schematics use potentiometer instead of R5. It must me about 100K … 1M range. After fine tuning, measure the resistance of potentiometer and replace with simple resistor with same nominal value.

Don’t forget to add capacitors near error inputs. Circuit is quite sensitive and various interferences can start the fan.

This small modification in the older schematics made it sensible to temperature.

Main difference from older circuit is that I used one of error comparators for NTC thermoresistor. R3 and R4 must be equal or something near to make temperature adjustments easy. As at this moment I have only one potentiometer at hand so I removed fan speed control.

more…

It is simplest PWM fan speed control circuit from scrap. The detail values are not very critical.

Here is the schematics:

R1-~10K, R2-~100K, C1- 0.01μF, chip- TL494, KA7500. It would be good practice to put some electrolytic capacitor between Vcc and GND near the chip.

Using potentiometer R2 you can adjust fan speed.

While PWM?
MAJOR PRO: Almost no heat is produced by the circuit – you can use it without a heatsink.
MAJOR CON: Since there’s no constant power for the circuitry in the fan, RPM sensing/failure detection will be erratic at best.

The schematics is simplified to the lowest level. So it may not work with some fans. On my testing breadboard it works with some fan from PSU (DC12V, 0.14A, brushless). The TL494 output power can be from 2×200mA to 2×500mA (depending on manufacturer). The fan current must be less than chip’s output current.

more …

In every schematic you can find few capacitors. Sometimes you remove old caps from some junk boards. And sometimes it is difficult to determine the cap value. There is some standards for cap coding, but not every manufacturer take care about it. The capacitance is measured in farads. But one farad is very big value, so people use fractional parts of it. These parts are decimal and called using old names:mili (m, *10^-3), micro (μ, u, *10^-6), nano (n, *10^-9), piko (p, *10^-12).

I have difficulties translating nanofarads to piko or microfarads. So I am using this picture. It helps me. Just imagine you cap value written on the picture and you can read the value in other form:

Standard says, that there are only two digits on the capacitor body, the value is expressed in pikofarads (47 = 47pF), if numbers are three the first two number show value and last is representing multiplication value, or just how many zeros you must add (472 = 4700pF). But in real world …

Just look at the scans:

In the first row you can see SMD tantalum caps. They never be in pikofarads , so two digit caps is in microfarads. Sometimes manufacturer print Greek letter mju – μ, to show that it is microfarads. On the second row there is another curiosity- the value of small cap is printed in mikrofarads- .0033, the leading zero is omitted. I think is is old matsushita or victor company in Japan cap.

Here is that tantalum with μ and other standard caps.

And here is old “European”, I think Siemens made capacitors. The “n” shows that value are in nanofarads. On far right the cap is without letter- value is in pikofarads.

On the top row is special capacitor for protection. One side is full of various certificates, while on other you can see very small print of value. On the bottom there is two identical caps made by different Chinese manufacturers.

And the best thing is, that always use multimeter to measure the value of the caps. Especially if you are playing with SMD ones.

As I wrote in other article, we received some old Japanese made old hardware. On Friday I opened some big device and removed few more lamps.

This was power supply. And one heavy used and another quite new 6AS7. Also 5AR4 and 12AX7. The power supply was repaired in circa 1984. And one 5AR4 was replaced with silicon diodes. Also removed some very nice and big inductors- 10H @ 100 and 250mA. Also very well made power transformers, but they were designed for operation in japan- 100V and 60Hz.