I have a Pioneer RT-701 on the bench. I've aligned and adjusted several reel to reel machines in the past but this one (and it's service manual) have left me with some questions.
First issue is that the VU meters (when mechanically zero'd) read differently from one another while injecting a 1k .316v sine wave into the line input jacks with the inputs bridged. This tells me I need to make sure my line input and vu calibration is correct before proceeding.
In the service manual there is a level diagram with some "test points" that reference the block diagram. It seems to state that .316v at the line input should show 1.99mv at point 8. Point 8 shows to be after VR903 and at the input of the FLAT AMP's first transistor base, labeled as Q205. This is a block diagram so it omits certain things that are present in the schematic.
The schematic shows VR903 as a trim pot on the Servo Amplifier Assembly and does not appear to be used as any sort of input trim but rather relating to the motor speed control. The boards are not marked for their component placement so the service manual must be used to identify test points and component placement.
If I'm not mistaken (and I certainly could be) it seems VR903 is NOT the input trim. Does anyone have any insight as to where to properly measure voltages to get the input side and VU's trimmed out before working on other aspects of the machine?
The machine was modified by a radio station for stereo half track use with different heads and then nearly abused in it's improper storage for years so I cannot assume any trim pots are in their correct positions.
I love the sound of the 707 and 701 machines when they work well, any help would certainly be appreciated!
First issue is that the VU meters (when mechanically zero'd) read differently from one another while injecting a 1k .316v sine wave into the line input jacks with the inputs bridged. This tells me I need to make sure my line input and vu calibration is correct before proceeding.
In the service manual there is a level diagram with some "test points" that reference the block diagram. It seems to state that .316v at the line input should show 1.99mv at point 8. Point 8 shows to be after VR903 and at the input of the FLAT AMP's first transistor base, labeled as Q205. This is a block diagram so it omits certain things that are present in the schematic.
The schematic shows VR903 as a trim pot on the Servo Amplifier Assembly and does not appear to be used as any sort of input trim but rather relating to the motor speed control. The boards are not marked for their component placement so the service manual must be used to identify test points and component placement.
If I'm not mistaken (and I certainly could be) it seems VR903 is NOT the input trim. Does anyone have any insight as to where to properly measure voltages to get the input side and VU's trimmed out before working on other aspects of the machine?
The machine was modified by a radio station for stereo half track use with different heads and then nearly abused in it's improper storage for years so I cannot assume any trim pots are in their correct positions.
I love the sound of the 707 and 701 machines when they work well, any help would certainly be appreciated!
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