Post by gjaky on Sept 9, 2016 13:40:38 GMT -5
Forum member jenum offered me two 909 neckboards that I couldn't resist to buy, one of them was known defective (but not he hybrid), so I decided to sacrifice it on the altar of science...
For the sake of completeness, here is how the Barco hybrid looks in its original form:
And this is after removing the RF shield box:
The first picture is from a newer neckboard, the second is an older one, note that they changed the peaking on the newer hybrids (2x75Ohm vs 2x220 Ohm and 1.2k vs. 330 Ohm). Also interesting to see how long bonding wire they used for connecting to the transistors, I would think this long wires are adding a lot of (unwanted) inductance EDIT 2020.05.07: but it is eliminating a lot of parasitic capacitance because the grounded heatsink tab is just underneath that area.
This is how the schematic diagram looks like of the hybrid, for reference there is the schematic of the Sanyo VPA hybrid.
There are further close-ups from the output transistors:
Q1:
Q2, please note the high frequency power transistors are often constructed of several "smaller" transistors tied in parallel, with an internal fuse, a part of these small transistors might burn out in an event of failure, still the overal transistor might remain functional, the grey parts circled, those parts are probably burnt out already, since this transistor still measures good from the outside.
Q3, was somewhat damaged when I ripped-off the RF shielding, still the transistor is functional.
Q4:
For the sake of completeness, here is how the Barco hybrid looks in its original form:
And this is after removing the RF shield box:
The first picture is from a newer neckboard, the second is an older one, note that they changed the peaking on the newer hybrids (2x75Ohm vs 2x220 Ohm and 1.2k vs. 330 Ohm). Also interesting to see how long bonding wire they used for connecting to the transistors, I would think this long wires are adding a lot of (unwanted) inductance EDIT 2020.05.07: but it is eliminating a lot of parasitic capacitance because the grounded heatsink tab is just underneath that area.
This is how the schematic diagram looks like of the hybrid, for reference there is the schematic of the Sanyo VPA hybrid.
There are further close-ups from the output transistors:
Q1:
Q2, please note the high frequency power transistors are often constructed of several "smaller" transistors tied in parallel, with an internal fuse, a part of these small transistors might burn out in an event of failure, still the overal transistor might remain functional, the grey parts circled, those parts are probably burnt out already, since this transistor still measures good from the outside.
Q3, was somewhat damaged when I ripped-off the RF shielding, still the transistor is functional.
Q4:
