╔═─────────────────────── ─────────────────── ──────────────────═╗ │ SOS...SOS...SOS... │ ╚═────────────────────────────── ──────────────────────────────═╝ (C) Klim If your computer fails, you can always turn to a specialist for help. But it often happens that masters who you can trust with your treasure cannot always be found. B In this case, we advise you to get out of the current situation on your own. situations. You don't have to worry that you never do it... were, because in most cases spontaneous computer outputs terov failures do not occur due to the loss of emissions of certain board components (in this case, find the faulty microcircuit without serious preparation will not work), but rather because of the created critical conditions for a computer, but not only. Today we We bring to your attention an overview of several repair tips your computer. Now we list the most common faults problems and ways to detect and eliminate them. Problem number 1. (The computer does not go to the initial menu). There can be a variety of reasons. Most often (20%) there is a violation of the electrical circuit of the computer due to denmarkdust, tiny particles of solder or metal chips, especially when using a metal case for a computer sa. The easiest way is to use an oscilloscope to view all the signals. ly, supplied and removed from the processor. All signals must have clear log levels. 0 and 1 should not have any pro- interstitial states created by two conflicting signals - mi. If you have discovered such intermediate states, then most likely In all, somewhere on the board such a signal “conflicts” with another signal in cash, and you just need to find such a place on the board. Sometimes such “conflicts” arise due to short circuits of conductors through flux residues that come out of vias in the board. It is necessary to look through the conductor with a suspicious signal throughout its entire length and clean doubtful places. Trouble number 2. (The computer freezes). It happens that programs are loaded and reset either immediately or after a short time. The reason for this The glitch may be the same as described in point 1., but it may The RAM chip may have failed (30%). Typically on screen in this case either points or rectangular squares appear the size of one familiar place. Often the nature of the manifestation of the fault is The voltage of this type changes when the supply voltage changes. niya +5 Volts. RevealRAM chip can be used using any test ROM that you should have on hand. If you don't know how to determine where on the board the identified faulty micro- RAM circuit, you can ring the processor data bus in- formation inputs of RAM chips (pin 2) and find the one you need IC. Sometimes the cause of failures in the operation of individual programs may be there may be a violation of the electrical circuit of the board due to inaccurate handling care during installation or transportation. Very often (20%) resistors are broken or cracked, especially when standing standing vertically. Problem number 3. (The computer does not respond to the keyboard). If your computer, which was previously working properly, suddenly stopped working with the keyboard, then most likely (90%) you exited building keyboard input multiplexer chips. Cause you- failure - induction of static and electromagnetic fields on The keyboard cable is long enough. These leads are derived from building the input stages of keyboard multiplexers. In good condition state at the 'Kb_inO...4' inputs there should be a level close to +5 Volt. If on any of the inputs when the keys are not pressed this level does not exist, which means that the IC to which this input applies. Identify this microcircuit and feel free to change it to working properly. If you have a problemof this type, then It's better for you to turn on anti-ringing diodes at the 'Kb_inO...4' inputs ground and +5 Volts, which will prevent such malfunctions in the future. It also won’t hurt if you connect the keyboard housing with the computer case with a separate wire (unless of course the cases are metal- personal), and make the keyboard cable either shielded or flat with alternating signal and ground wires. Problem number 4. (The computer does not read information from the drive) This is one of the most common faults (70%). In case When such a malfunction occurs, it usually appears on the screen error message about reading from track zero, sector nine. First of all, you need to make sure that the disk drive itself is working properly. yes, and only then panic. If the disk converter is working properly, then check The drive controller IC is based on 1818VG93, as a rule, it is installed pours onto the socket, and its check is reduced only to availability spare mini. If no changes occur, then it is necessary check the presence of +12 Volts at pin 40 of the VG93. If all the above the listed elements are in good working order, then most likely it has failed PLL IC. In this case, as a rule, the drive motor works, and The drive moves when you first access the drive. Additional A significant sign of a faulty PLL IC is incorrect signals on 26 and 27 pins. VG93. INin good condition, when handled connection to the drive, on pin 26 there should be pulses with a period of 4 μs, which “tremble” a little - the frequency is adjusted drive synchronization pulses, and at pin 27 there are short negative pulses with the same frequency as at pin 26. Very often, you can eliminate such a malfunction by choosing to work bots an unused part of the PLL IC. If at this stage there is no the serviceability is not eliminated, then you should check the serviceability of the ferry chips working on the disk drive. Problem number 5. (The computer does not format floppy disks, but loads programs). Almost always (80%) the cause of this malfunction is failure of the IC drive controller 1818VG93. So first It is necessary to replace this device with a known good one. If this did not help, then you should check the serviceability of the disk drive (5%) and connecting cable (5%) from the board to the drive. Besides this, The cause of this type of malfunction may be damage to the circuit board (3%) or short circuit (3%) due to foreign micro- particles, as well as defects in the panel lamellas for 1818VG93 (15%). I am aware that with this list I have all possible I didn’t list the faults, but these are really the most common 'diseases' of our computer. If the cause is yes fromcomputer malfunction is not a 'disease', but rather its 'trauma', then an individual approach is required. For those who like his computer, in terms of 'hardwired' in non- set of software such as BASIC, DOS and others, I advise you to save a dump of these on a floppy disk just in case programs. Since 'eternal' memory chips are not eternal at all, and They also tend to fail. That's all for now, I wish your computers not to get sick, and work thief reliably. Klim Gromov. (095) 366-6569 (Sergey)
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