Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Posted to sci.electronics.repair
b b is offline
external usenet poster
 
Posts: 764
Default grundig vcr - gv9000 - erase problem

This VCR was not fully erasing tapes, symptom being incomplete erasure
of chroma and hifi audio on most tapes. No voltage was found at the
erase head pins when in REC.

Opened it up and found R662 , 4R7 burned open. Replacement did the
same, but strangely it did so from switch on - the record circuit was
not energized. Not sure how significant this is - presumably this
means there may be a problem with the 12v coming from the BA7755
(pin1) into choke L652? Would I be right in suspecting the amplifiier
transistor Q654 (2sc3203)

here are some scans of the circuit.

this one is a close up of the oscillator stage, http://www.mediafire.com/?5qmy6qj6y060p2w

this one is the general area, with visible lines to heads and supplies
http://www.mediafire.com/?6na5n8dhgroee4c

....any thoughts appreciated.
B.
  #2   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 667
Default grundig vcr - gv9000 - erase problem

On Fri, 29 Oct 2010 15:46:16 -0700, b wrote:

This VCR was not fully erasing tapes, symptom being incomplete erasure
of chroma and hifi audio on most tapes. No voltage was found at the
erase head pins when in REC.

Opened it up and found R662 , 4R7 burned open. Replacement did the same,
but strangely it did so from switch on - the record circuit was not
energized. Not sure how significant this is - presumably this means
there may be a problem with the 12v coming from the BA7755 (pin1) into
choke L652? Would I be right in suspecting the amplifiier transistor
Q654 (2sc3203)

here are some scans of the circuit.

this one is a close up of the oscillator stage,
http://www.mediafire.com/?5qmy6qj6y060p2w

this one is the general area, with visible lines to heads and supplies
http://www.mediafire.com/?6na5n8dhgroee4c

...any thoughts appreciated.
B.


Pin one of the BA7755 is the Vcc of that chip and is supplied 12.9v via
the choke as is T652. Look for a way for that voltage to get back through
Q654 and R662 to erase ground to provide enough current flow to destroy
the resistor.



--
Live Fast, Die Young and Leave a Pretty Corpse
Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
GRUNDIG SHAVER - battery problem? b Electronics Repair 7 November 12th 07 10:47 PM
Grundig TV Problem [email protected] Electronics Repair 1 March 12th 06 11:32 PM
Grundig VS 505 VPS problem Damir Electronics Repair 0 January 4th 05 08:41 AM
grundig flyback problem a'af Electronics Repair 1 June 15th 04 11:17 AM
Grundig ST 55-750 problem NieuwsGroep Electronics Repair 1 September 21st 03 02:23 PM


All times are GMT +1. The time now is 10:10 PM.

Powered by vBulletin® Copyright ©2000 - 2023, Jelsoft Enterprises Ltd.
Copyright 2004-2023 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"