UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players

Notices

Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

Closed Thread
 
Thread Tools
Old 20th May 2022, 6:37 pm   #1
hallwod
Triode
 
Join Date: May 2019
Location: Flitwick, Bedfordshire, UK.
Posts: 21
Default Revox A77 MK4 Dolby Calibration

Currently working on this deck. I've re-capped all boards including the two Dolby processors.

I started on the Dolby calibration and successfully did the first part - The record processor.

However, I've run into a problem with the Dolby play back calibration.

I've set up my signal generator at 5kHz output about 3mv and attached this to P5 and ground

Attached my millivoltmeter to P7 and ground - no output!

I checked the voltages on the playback card transistors (from the schematic) and all appear to be OK.

Any suggestions as to where I should be looking next?
hallwod is offline  
Old 30th May 2022, 9:49 am   #2
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Revox A77 MK4 Dolby Calibration

Have not had a chance to look at the schematic but I would suggest using a scope |(if you have one) to check the injected signal through the transistors to see where it is being lost and then work out why.

David
DMcMahon is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:25 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.