A Revox B77 MKI managed to find its way into my collection of audio toys.
Included in the trade...
The QC checklist - 1982.
The Specifications p33
Specifications p34
This machine was originally the Low Speed version, with 3¾ - 7½ IPS Record/Playback speeds, later converted to a High Speed, 7½ - 15 IPS. This modification required a high speed capstan motor, in addition to various other electronic modifications.
Before powering it up for the first time - it was in storage for a couple of decades - I removed it from the case to look for any signs of burnt, bulged, discolored, or missing parts. I was curious about user experiences with this machine - e.g. common failures, tape and maintenance recommendations, etc. A fantastic place for this is Tapeheads.net.
Tape! Not something that you can find at your local audio store... so I ordered a reel of ATR Master Tape. Another source is Full Compass.
Once I got the tape, I hooked the machine into a Gaines audio converter, to feed the Crown D45 amp, driving a pair of B&W DM602 S3 speakers.
Before powering it up for the first time - it was in storage for a couple of decades - I removed it from the case to look for any signs of burnt, bulged, discolored, or missing parts. I was curious about user experiences with this machine - e.g. common failures, tape and maintenance recommendations, etc. A fantastic place for this is Tapeheads.net.
Tape! Not something that you can find at your local audio store... so I ordered a reel of ATR Master Tape. Another source is Full Compass.
Once I got the tape, I hooked the machine into a Gaines audio converter, to feed the Crown D45 amp, driving a pair of B&W DM602 S3 speakers.
D45
All is good - for awhile...
Electronic components age - just like anything else. One of the most common issues is the failure of electrolytic capacitors - as they age, they open, short, or turn into some resistive value between zero and the infinite. This can cause any number of problems - anything from not passing audio, to flames jumping from the power supply! The other issue is the tantalum capacitors. Tantalums like to explode - that's another story...
I wanted to make a recording. The machine had been working perfectly - yet this time, the audio was extremely low in level. Often, reseating cards and various connectors, exercising switches, can solve the problem - as contacts oxidize and signals get messed up. Not this time!
The next step was locating a service manual. First, I checked the main power supply voltages - all were within specification. Then, I pulled out each circuit card to look for visible damage.
Well that was easy to spot...
Burnt resistor! Now, why did it burn...
R6 is the burnt resistor, upper right...
The underlined component, a 47Ω resistor, was toast. The circled component, C6, is (well, was...) a 220uf 25v electrolytic capacitor - that due to age, turned into a 20Ω resistor - causing excessive current to flow from the +21v rail to ground - and taking out the resistor.
At this point, I made made the decision to simply replace all of the electrolytics - so I made an inventory - comparing the actual circuit cards to the service manual, and ordered the parts.
Once I get the parts and get everything replaced, I'll post an update.
