Posted by wunhuanglo [ 68.222.11.132 ] on June 25, 2005 at 11:37:40:
I have some D-75As I wanted to convert to mono, but the manual has no instructions other than to take them to a Crown service center.
I really didn’t want to spend 25% of the cost of the amps to get them converted at a service center, so, being a Nervous Nellie of the first order I tried for ages to get definitive info about how it’s done – no dice, not even from Crown.
Finally, with no other options on the horizon, I grabbed the bull by the dangly bits and did them myself. For reference, here’s how it’s done:
1. Loosen the (4) rack ear screws – no need to remove them; T-15 Torx
2. Pull rack ears back from case by about 1/32 inch
3. Remove (6) cover screws, three each side; #2 Phillips. The screws nearest the front are machine screws, the paired screws nearest the back are sheet metal screws – note the difference before replacing them.
4. Pull cover back from faceplate where it’s inserted into a slot running along the top; remove cover
5. Remove (4) sheet metal screws, two each side, from XLR connectors at rear panel; #1 Phillips
6. Remove (4) bright steel sheet metal screws and internal tooth lock washers, two each side, retaining input board (green PCB at rear-right of amp); #1 Phillips
7. Lift input board from front edge to disengage two connectors engaging two pin headers.
8. Gently work board forward to clear XLR connectors from rear panel. The board is still connected to amp by wire leads and cannot be lifted free without desoldering – removing board completely is not necessary
9. Stand board up on front edge, exposing bottom
10. Near the center-top find “mono-dual” pin header with PCB-style jumper
11. Move jumper to “mono” – two left-most pins.
12. Reassemble in reverse order. Be careful that all wires clear pin headers before engaging input board at front edge. Tighten transformer mounting screws (which will be loose) in vain hope of quieting transformer vibration. Note that underside front-left of cover has a strip of tape to insulate the cover from a strip of wiring lugs inside amp – make sure tape strip remains in place before replacing cover.
13. Note with utter delight that half of the screws retaining XLR connectors are probably stripped out – hope that 1 at each connector holds.
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