McIntosh MI3 Vertical Control

borhbemo

New Member
My MI3 has limited vertical control (cannot move the "test dot" beyond about an inch below the centerline). The device works fine on both multipath and L/R audio, but for both the display is "squished" into a more or less horizontal line with pulses showing on the horizontal but not vertical (no "squiggly ball" on the L&R Audio). Is this a CRT issue, a tube issue, or something else?
 
My MI3 has limited vertical control (cannot move the "test dot" beyond about an inch below the centerline). The device works fine on both multipath and L/R audio, but for both the display is "squished" into a more or less horizontal line with pulses showing on the horizontal but not vertical (no "squiggly ball" on the L&R Audio). Is this a CRT issue, a tube issue, or something else?
Could be a tube or passive circuit problem, CRT problem unlikely.
 
Thanks for the quick reply! Will check tubes as easiest first step. A quick search on "passive circuit problems" points to a variety of possible faulty components. Any recommended troubleshooting tips to narrow down further?
 
If you (or someone) could post the schematic, I could look for the usual likely suspects.
 
Here's the schematic. First time uploading pdf to this board...hope its readable. Thanks again.
 

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  • MI3 Schematic0001.pdf
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yes, i get a little movement down and up (maybe a 1/4 inch on the display) to the max vertical position, which is closer to 1/2 inch (than inch) below the horizontal guide line in the middle of the scope.
 
No change when swapping tubes in positions V1/V2 with V3/V4. Still same limited (1/4 inch) vertical movement, unlimited horizontal movement
 
I'm a multimeter novice--find Q1 and Q2 on the schematic, but don't know where to test the voltages (i.e. translate from the schematic to where to place leads and what to look for in voltage readings).

Sounds like we've eliminated tubes as the cause, which likely narrows it to a circuit problem. So...looks like the unit heads to the shop for a professional to test when time/money available. thanks again for the assist!
 
I'm a multimeter novice--find Q1 and Q2 on the schematic, but don't know where to test the voltages (i.e. translate from the schematic to where to place leads and what to look for in voltage readings).

Sounds like we've eliminated tubes as the cause, which likely narrows it to a circuit problem. So...looks like the unit heads to the shop for a professional to test when time/money available. thanks again for the assist!
Probably for the best then, a bad transistor is a possibilty.
 
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