tech 1200 pitch warble

mixhard · 10th April 2006, 05:46 AM

A friend of mine tried to upgrade the pop up lite in his 1200mkII and the orange wire shorted out which he was trying this... i immediatly told him to stop what he was doing. I checked the voltage at the wire and it sits around 30volts. The problem is the pitch wobbles like crazy and pretty much any spot on the pitch control. if i turn it off then on and have the pitch around zero... its seems fine till i move the pitch fader. then it warbles again. I was wondering what the 1.5kohm resistor is doing across the micro switch for the pop up light as well.

mixhard · 10th April 2006, 10:04 AM

another thing i noticed is that the strobes brightness changes with the warble in the pitch. I beleive that the power for the light also feeds the strobe and the speed control circuit. Is that correct?

Netlist · 10th April 2006, 12:38 PM

The stylus illuminator is directly connected to the +B which is 21V. It has a 1.5k resistor in series with ground to limit the voltage.
The strobe is fed by a 150 ohm resistor to +B.
If +B is 30V, you should check Q1, Q2 and Q3. Q1 is the transistor located on top of the PCB board and attached to the main chassis for cooling. Q2 and Q3 are on the main board.
Let me know your findings.

/Hugo

10th April 2006, 05:46 AM	#1
mixhard diyAudio Member Join Date: Apr 2006 Location: Winnipeg Manitoba	tech 1200 pitch warble A friend of mine tried to upgrade the pop up lite in his 1200mkII and the orange wire shorted out which he was trying this... i immediatly told him to stop what he was doing. I checked the voltage at the wire and it sits around 30volts. The problem is the pitch wobbles like crazy and pretty much any spot on the pitch control. if i turn it off then on and have the pitch around zero... its seems fine till i move the pitch fader. then it warbles again. I was wondering what the 1.5kohm resistor is doing across the micro switch for the pop up light as well.

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10th April 2006, 10:04 AM	#2
mixhard diyAudio Member Join Date: Apr 2006 Location: Winnipeg Manitoba	another thing i noticed is that the strobes brightness changes with the warble in the pitch. I beleive that the power for the light also feeds the strobe and the speed control circuit. Is that correct?

10th April 2006, 12:38 PM	#3
Netlist diyAudio Moderator Join Date: Jan 2003	The stylus illuminator is directly connected to the +B which is 21V. It has a 1.5k resistor in series with ground to limit the voltage. The strobe is fed by a 150 ohm resistor to +B. If +B is 30V, you should check Q1, Q2 and Q3. Q1 is the transistor located on top of the PCB board and attached to the main chassis for cooling. Q2 and Q3 are on the main board. Let me know your findings. /Hugo

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