I was on the search for a small 1U reliable power amplifier that I can use to power my audio oscillator. Together I take these 2 units in a small road case and use them on the go to test speakers or speaker cabinets. When you send the sine wave through the speakers 20hz to 20khz in a sweep you can use this to identify issues with the speaker cone, coil or spider. Abnormalities will produce a rattle, hum or distortion. It’s a good check also when buying second hand speakers/cabinets. I didn’t want to spend a lot on this amplifier since it’s only used for testing.
I choose the Crown D-75 because it’s has been an application monitor amplifier standard for many years. Typically used in broadcasting it will serve it’s purpose for my testing setup. I found a real cheap one online that had some issues. After opening I found corroded chokes, a burnt ceramic resistor, missing power switch and a bad audio pot.
This is the version that does not have any labels on the main board so make notes when you open (very carefully) before all the connections pull off of the board. If lost please use the photos for reference or the attached documents.
open unit crown d-75 
lifted main board with wires attached 
power supply and caps 
burnt resistor 
connections-1 
connections-2 
connections-3 
Corroded Chokes
So a really quick repair, removed all bad chokes and installed new ones (.5mH RF Choke, same as 500uH) Removed any burnt ceramic resistors and replaced with CP-5 Dale 5W .1 10% ceramic. Changed the rotary power switch with a standard toggle, replaced the R101 R201 with a 25K audio level taper pot. This unit is rugged so the main components are solid. Notes: keep in mind there are 2 grounding wire that will need to be de-soldered from each board before you lift. Use a deoxit spray on all connections since the unit is older. The hardest item to find is the RF choke. I bought these on ebay for a reasonable price (see photos).
