Atari Vector Monitor Repair/Upgrade

Contents: Green too bright

On neck board: No green + blue is red

On neck board: Green is red

On neck board: Green does not turn off when dimmed all the way

On neck board: No blue

On deflection board: On neck board: Only blue

On deflection board: Blue does not turn off when dimmed all the way

On neck board:

  10.4) High Voltage Board Problems

    10.4.1) Display unstable

The image is extremely shaky and unstable and lines that should be straight have periodic wiggles along their length that make them look like an EKG (the distortion is sort of like when you watch TV with a bad antennae and lines "walk" around on the screen).

Replace C901, C902, and/or C905 in the HV supply. If of these is bad then the rest of the electrolytic capacitors are probably in pretty poor condition too, so I generally replace all of them. Make sure the replacements are rated at as least as many "working volts DC" WVDC and have as least as many micro-Farads. It doesn't hurt to replace a 22uF @ 50V capacitor with a 50uf @ 100V if that is all you have around. More Voltage capacity is equal or better but it is best to keep the capacitance the same if you can. Also when ordering and replacing these, be aware that they are polarized and not idiot-proof; be sure to put them in the circuit so that they are oriented properly. The casing will clearly indicate either the negative or the positive terminal (but typically not both) and the industry convention is for the positive lead of the capacitor to be longer than the negative lead. Be aware that P329 has an extra capacitor (C22) that may not be shown in your manual; its value is 10uf at 63V.

    10.4.2) Picture too bright but all else OK

The picture is overly bright and all parts check out OK.

Look for a broken circuit board trace between pin 6 of the high voltage transformer and the anode of diode D901. This trace is prone to breaking open. It is probably easier to just add a jumper and see if it solves the problem or else check the connection (with board removed) with a meter to make sure it is a short.

    10.4.3) R925, R919, and R917 are smoked

    10.4.4) R901, R907, R903 are smoked and Q902 and ZD901 are shorted

    10.4.5) Top of Q901 blowing off

    10.4.6) Top of Q902 blowing off

    10.4.7) R901 and R907 are smoking

    10.4.8) Just R901 smokes

    10.4.9) R903 smokes

    10.4.10) R904 smokes

    10.4.11) R907 smokes

    10.4.12) R908 smokes

    10.4.13) R912 smokes

    10.4.14) R917 smokes

If R920 smokes, check:

  10.5) No HV (very dead sound)

No High Voltage (HV); you don't hear the crackling sound when you first turn the monitor on.

Check the transistors in the HV unit as described earlier. The ones I've seen fail most often are Q903, Q902, and Q901 though they are all suspect. These transistors will usually have cracks in the casing if they are bad so look closely at them. If all this stuff is OK, look at the electrolytic capacitors (they are the big cylindrical tube-like parts and are usually blue in color) in the circuit. They come in two "types":

   _____                      |   |
 --|   |--         axial-lead |   |
   ~~~~~                      +---+
 radial-lead                   | |

One quick errata: The parts list in Figure 15 of TM-183 lists all capacitors as fixed axial-lead when in reality only C905 is; the others are all radial-lead. These are designed to burst open (VENT) when they fail due to overburdening (but they sometimes don't) so as to be obvious to repairpersons. The top (for radial-leads) or the side (for axial-leads) will be open and some of the "guts" will be hanging out. When some capacitors go bad, they sometimes take the final output resistors R901 and/or R907 with them (but the resistors will look perfectly OK unless you check them with a meter). Also check to make sure that connector J901 inside the HV unit is intact; on person reported that the plastic in his disintegrated on the inside and the wires came loose. If these are OK, check the following:

    10.5.1) Waveform at IC901 outputs; if missing, check

    10.5.2) Waveform at Q906; if missing, check

    10.5.3) Waveform at Q905; if collector wrong, check

    10.5.4) Waveform at R921; if wrong, check

    10.5.5) IC901; if no input voltages, check

    10.5.6) IC901; if input voltages present, check

    10.5.7) If you are also blowing any fuses, check

    10.5.8) F600 blows immediately on powerup

Replace R612 if open.

    10.5.9) Blooming/"weak" brightness/Low HV

Most of you don't have a HV probe but the most common symptom of low HV is that the screen looks as though you are looking at the center through a magnifying glass. This visual symptom is known as "blooming". I've seen several times where ZD902 (150 volt Zener diode) goes bad and the HV drops from 19.5 kilovolts to around 10 kV. It's kind of like the electron beam moves slower with less HV giving the deflection magnets on the yoke more time to deflect the beam (but what is really happening is that there is not enough HV to strip all of the electrons off of the phosphor coating which causes the screen to develop a negative charge which then deflects new electrons which are expected to be hitting a screen with no charge on it). A new ZD902 and everything is better. NTE5100A is a common modern day replacement for this part. If ZD902 is OK, check the following:

  10.6) HV range wrong, what causes it?

Normal is 16-24 kV

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