[analogorgans] Re: Rodgers Specification 990
- From: Walt Scrivens <walts@xxxxxxxx>
- To: analogorgans@xxxxxxxxxxxxx
- Date: Sat, 5 Jan 2008 13:15:31 -0500
Thanks you, everyone!
I replaced D10 with a Radio Shack 5A, 50PIV rectifier diode, set the
power supply to 12V and installed it. 50 or so push-on connectors
later the organ is working again!
So, after 2 hours' work and less that $1.00 in parts, with a lot of
help from this group, the "uneconomical to repair" organ is working
again, Praise the Lord!
Many thanks for all the help :-)
Walt
On Jan 1, 2008, at 4:19 PM, Don W. McClure wrote:
Hi Walt--
The D10 diode is designated as an SS-1 in my manual (printed August
1970 for instrument SN 38057).
An electrical engineer's opinion: This diode is in series with the
Q1 emitter-collector circuit, as you already know from both
schematic and physical tracing. Regulation of +12V is probably
depending on a 1.4V known drop across R3 (100 ohms), and D10 is
carrying the current load for +12 V in the organ itself. I have
not measured the current load at that point in my instrument,
although other list folks have mentioned significant drops in
voltage from no-load to loaded conditions.
I believe a standard 50-PIV rectifier would probably work (fast-
recovery, if you can find one) --but I tend to think current
handling is in order here as well (probably 6 A or better).
Frankly, I believe the odd installation is a giveaway....this
rectifier is a current-handler, and should be heatsink-mounted.
Curiously, the diagram in my book does *not* show it on the
heatsink! I know you already realize potential power dissipation--
but for other readers who might not, this diode will be dissipating
3.3-4.2W at a 5-6 A current draw (this leg alone).
I have not needed to service the power supply in my instrument yet,
so I cannot confirm this diode's status by direct observation. Hope
this information helps.
Don W. McClure, P.E.
electrical engineer
990 at home
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