Hi there. From the description, I understand the problem to be a
proliferation of raised, black spots and also yellowing leaves. I
checked the troubleshooting section of my best orchid book and here's
what I came up with:

a) Insects & Mites: scale insects appear as brown, white, or grey bumps
on leaves, stems, and flowers. Severe infestations can cause yellowing
and stunt the plant. Remove scale using a swab dipped in 70% denatured
or rubbing alcohol.

b) Diseases: fungal infections often create black spots but they are
sunken--not raised. Black spots could also be caused by a virus, but
there's no treatment for that. And it doesn't say they're raised
either.

c) Problems in the Environment: This section shows a leaf with raised,
black spots and states that the condition resulted from underwatering
(underwatering that attracted scale to the leaves). Later in this
section, it says that symptoms from too much fertilizer include burnt
leaf tips. And still later in this section, too much light results in
yellowing of the plant.

Based on the troubleshooting guide, it sounds like the plant is
expressing multiple environmental issues. Underwatering may have
attracted scale that shows as the symptom of raised, black spots.
Overfertilization shows in the burnt leaf tips. And excess light shows
in the general yellowing of the plant.

The response of treating the scale with denatured alcohol, watering a
little more frequently, fertilizing less often and/or with weaker
solution, and reducing the amount of light would help this plant.

Disclaimer: I'm not a pro. So you might want to get a second opinion
before taking action. I've read about 7 books on orchids but this one
is my favorite and contains the troubleshooting guide I used to write
this email: Ortho Books Complete Guide to Orchids. They sell it,
surprisingly, at Home Depot in the garden section. I know--Home
Depot--but it's really more informative, accurate, and current than
books I've found and read at other boutique shops and at the library.

Hope this helps! Let us know how it works out.

-Munir

P.S. I have six orchids and just discovered, earlier today, that three
of them--all from the same vendor--are suffering from some infestation
and rot. The reason, I suspect, is that the vendor sold them in the
wrong potting material that harbored bugs and also encouraged root rot.
The other three--from other vendors and that were in great potting
material with they arrived--are doing just peachy in the same
conditions. All were repotted about 2 months ago and are receiving the
same treatment. So sometimes it's not only your care but also the care
or potting situation that you inherited that can cause problems. My
belief is that if you don't lose the plant entirely, it should recover
with proper treatment and culture. -M