from that above link I am posting the following re an important update that PY22285 did:-
DO FYI His Note: I am not fluent in English, so that this text it was translated with my few knowledge of the English language, and using an electronic translator, don't wait a
perfect text, but I believe that this can be understood perfectly.
and when I look at my version V50B it has a crappy little tubular (like an electrolytic cap) inductor.
So I think this will be a a TASK to correct and improve my unit.
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Improving converter DC-DC.
The "heel of Aquiles" of this version of willem is DC-DC converter, that generates the different voltages to Vpp (12.5, 15, 21 and
25V).
The main item that cause a series of problems is the coil, which must have mass to not saturate with the drain demanded for
eprom in the programming. The biggest problem is in the programming old eproms , which demands much current in the Vpp.
The maximum current supplied by the converter in my original board was of only 35mA approximately, what he is little for some
eproms.
To obtain coil of 100uH that it has supported a current up to 100mA without saturating is something complicated, therefore the
majority them coil, and XRF found in the commerce has nucleus very small e saturates quickly with currents of this order. Solution?
mproving converter DC-DC.
The "heel of Aquiles" of this version of willem is DC-DC converter, that generates the different voltages to Vpp (12.5, 15, 21 and
25V). The main item that cause a series of problems is the coil, which must have mass to not saturate with the drain demanded for
eprom in the programming. The biggest problem is in the programming old eproms , which demands much current in the Vpp.
The maximum current supplied by the converter in my original board was of only 35mA approximately, what he is little for some
eproms.
To obtain coil of 100uH that it has supported a current up to 100mA without saturating is something complicated, therefore the
majority them coil, and XRF found in the commerce has nucleus very small e saturates quickly with currents of this order. Solution?
Making a new coil, using a toroid core. The place to find an ideal nucleus is the box of scraps. Seeking I found toroid cores in old
mother-board of PC and in battery charger for cellular phone, for vehicular use. Besides in these last ones, also found the MC34063
or the JRC2360D that it is direct equivalent, done made by Japan Radio Co. LTD. Below see a board of these battery charger.
The coil can be used directly, it is enough remove and to place in the board. In the case of re-taking use core from PC Board, the
coil should have been re-wound. See the same core in an old board "PC-chips SiS530":
This is the dimensions of the core for who wants to seek a similar one in another board:
Height: 5mm
Internal diameter: 8mm
External diameter: 13mm
Color of core: I yellow with a white border.
Remove original coil, and wind 55 turns of 24AWG enamel wire distributed uniform on the core.
Other modifications that seek a better performance in the DC-DC converter:
Replace:
Transistor Q4, original: BC557, change to BC327 or BC328.
Resistor R9, original 2K2, change to 1K2.
Resistor R17, original: 0.5Ω, change to 0.33Ω In case doesn't find, do use my solution, 3 resistor of 1Ω in parallel,
what will give us exactly 0.33Ω.
Capacitor C2, original: 220pF, change tor 1nF, it seeks to lower chopper frequency.
Diode D3, original: 1N4148, change to BYV26, BYV95C or other any scotky diode.
The voltage regulator, 7805 more heat a little more than the normal, is convenient to place a small heatsink. It is finally, use a
GOOD power supply, I am using one from an old scanner, of 12V x 1200mA.
With these modifications, the current supplied by the DC-DC converter, up-to 100mA. The block of schematic below were made
the modifications, the components in blue are they mentioned above.
Protecting PIC against mistakes in the adjustment of Vpp.
The poor of the pics are the largest ones you slay in case you change the Vpp for 21 or 25V and forget to come back the jumps for
the position of 12.5V.
Myself already made twice this mistake and burning two PIC16F877A.
The solution for that is simple, it is enough to add a resistor in series with the line of Vpp, that is going to the ICS connector and
for 18 pins socket. And a zener diode to limit the tension in a safe value.
If you already made here this modification, it is necessary to move wire for the other extremity where was the jump, because I
marry I thwart in this point the modification it will be tied up to protected Vpp of 12V of pics and not more to direct Vpp after the
modification. In the illustration I already placed the resistor (in blue) that will be added in the place of the jump.
The modification in the board is quite simple, it is not necessary to cut any track, it is enough to remove two jumps and to
proceed the modification. In the photo below show the position of the jumps, and notice that already installed the resistor 560R in
the place of one of jumps, the other jump is empty.
Inside of ellipse 1, a jump was removed and ellipse 2, the jump was removed and installed the resistor of 560R x 1/8W in its
place. Now it lacks only a small bridge on the side under the board and to install the zener diode, 13V x 1W, according to the
photo below.
The yellow rectangle indicates the socket of 18 pins. The wire that passes on the socket of 18 pins is the bridge that should be
added. Already take advantage of and place the resistor of 1K that this in the pin 10 of the socket, linked to GND. This resistor
ground the pin Low Voltage Program, of the PIC16F628. The diode zener this with its anode attached to the pins 1 and 2 of the
socket of 24Cxx. With this this modification this completes.
