After posting my query on this list about the motor for the 87a blower, I
received a number of email messages of encouragement, to try to repair the
blower that I had... I also called RF Concepts on 12/21, and ordered a new
blower assembly. I reasoned that I might be able to repair the one I had, and
having another blower around might not be a bad idea.
Armed with the instructions on how to do the replacement from the RF Concepts
web site, I started in on the amp at 9am Christmas Eve. I counted at least 39
screws that needed removal, NOT including the cabinet nor power transformer. I
used some plastic divided containers to hold parts as I went through the steps,
and marked up a printed copy of the instructions as I proceeded. About 1.5
hours later, I got to this point, with the 87a spread all over the table:
https://ws.onehub.com/files/bkr8xy7g
It helped to read a little ahead -- step 2.3 performed before step 2.1 makes
step 2.1 easier. Holding the tube deck up enough to get a screwdriver in while
performing steps 2.7 and 2.8 really helps alot, and can avoid using a right
hand screw driver.
Seems like there should be a step 2.9 to remove two 6-32 screws from the rear
panel holding in an aluminum piece. Also, with the A/C module removed, it's
not a problem to remove the three 6-32 screws and washers from all three nylon
cable clamps to free the fan cable without snipping the wire to the connector.
I removed the blower assembly; the one that I had is a Howard Industries
1175-16-4732 - https://ws.onehub.com/files/2si71tzz
(note that at the time of original construction, one of the motor leads was
been pinched between the rear panel and the central divider -- see the picture)
The one that I have will break down into motor, blower wheel, blower shroud,
insulated L-bracket, however the motor itself was riveted together.
Furthermore, the shaft is fixed at one end, and the motor's stator turns on a
sleeve bearing around it. The motor didn't smell burned, nothing looked cooked.
I did notice a small solder blob fell out of the assembly as I examined it from
all directions. I found that the motor would blow air just fine when 220v was
applied (outside of the amplifier). Could the solder blob have been jamming it
up?
Here are all of the parts: https://ws.onehub.com/files/nfiho9d4
I tore down the assembly into it's parts to clean it. When I removed the piece
of plastic to which the blower wheel was screwed, it revealed an O-Ring, the
sleeve bearing, and what looked like some dried oil, along with some thin
plastic shims. I cleaned up this area, and with the shaft vertical facing me,
applied a general purpose oil (Zoom oiler), letting it go through the sleeved
bearing. I applied enough oil to build a little pool to the edge of the o-ring,
and watched it see that it wasn't leaking. The blower housing was attached with
a single screw and what looked like (now dried out) coax-seal -- some sort of
asphalt-y material that stuck the housing to the L-bracket, and also absorbed
vibration. Using a water soluble citrus cleaner and a plastic scraper, I
removed the old stuff, and reassembled with a strip of coax seal with the same
dimensions. I re-attached the plastic piece that seals against the o-ring,
re-attached the blower wheel, and ran
it for an hour on the bench to watch for leaks -- there were none.
(picture of the O-ring and shaft end of the motor
https://ws.onehub.com/files/7vmc2e4p )
Re-assembling the was indeed the reverse of the dis-assembly -- the plastic
trays helped to make sure that all steps were completed in order, with no
screws forgotten.
About 10 minutes AFTER I got the tube deck re-installed, and just before the
T/R switch was going back in, Fedex delivered the brand new blower assembly! It
was a tough choice, however I opted to continue re-assembly with my
reconditioned assembly - If it fails, I know how to put the replacement in!
Some pointers on re-assembly: My 4th grade son got steps 2.7 and 2.8 while I
held up the tube deck and t/r assembly -- it really helps to have those extra
hands. Also, if you have a headlight, it helps when doing stuff while the amp
is on it's side.
The moment of truth arrived after I checked all of the connectors, plugs, etc.
three times, and even had my wife come over
Me: Honey, tell me if anything looks out of place
Her: How should I know, I don't even know what that is.
Me: see any wires that look disconnected or funny? see anything sticking out
that maybe shouldn't?
Her: Wow, there's a lot of stuff in here. All of it looks like it's connected
though. What's that part do?
Me: That's the tank coil. It tunes to the frequency that we're amplifying.
Her: All right then. Looks good!
Cover on, all screws in place, power on -- ventilation, self test passed, three
minute timer -- we're good!
A few contacts later, being left on all day -- still working great.
I'll take a picture of the new blower assembly in the next day or two and post
that -- but it looks very similar to what's been in this amp since 1991.
-Brian N9ADG
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