Revox B77 Logic Problem

kfalls

Active Member
Jun 24, 2015
34
0
36
Hi All,
I'm currently working on a Revox B77. It has a logic issue where the function buttons are not doing anything. All voltages and fuses are good and capstan is currently turning. My problem is the Tape Drive Control schematic I have has a different IC4 than what is on the board. The chip I have is an LS7402 and not the SC10429 24-pin shown on the schematic. I figure this is an earlier version without the tri-state chip. I've looked online, but all have the 24-pin chips. I've checked the label and I definitely have a B77, but certain it's not a MKII. I'm sure someone here can provide an answer.

Ken
 

kfalls

Active Member
Jun 24, 2015
34
0
36
I noticed this circuit earlier when checking PS voltages and noticing it wasn't supplied by the power supply. I didn't see +5V on the emitter, so assumed it was open. Q18 and D9 (5.6V Zener) provide +5V for the logic. Without your schematic I wouldn't have determined no signals were getting through the logic. Thanks again for the help.
 

About us

  • What’s Best Forum is THE forum for high end audio, product reviews, advice and sharing experiences on the best of everything else. This is THE place where audiophiles and audio companies discuss vintage, contemporary and new audio products, music servers, music streamers, computer audio, digital-to-analog converters, turntables, phono stages, cartridges, reel-to-reel tape machines, speakers, headphones and tube and solid-state amplification. Founded in 2010 What’s Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals, we enjoy learning about new things and meeting new people, and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing