Help! I need a fresh pair of eyes to look at a VERY mysterious problem I am having with a repair.
I am repairing a 582 that has lost the ability to record/erase tapes.
I have replaced the faulty caps in the bias oscillator and checked the frequency. The bias oscillator function has been restored and is right on spec.
I was just about to start checking/calibrating the deck's EX/SX/ZX record bias, when the deck lost its ability to go into PLAY mode.
It simply cannot enter PLAY mode. When you hit PLAY, the deck goes into PAUSE mode instead.
PAUSE = PAUSE PLAY = PAUSE
I have checked the reference voltage at the sliding contact of the cam control
10k volume pot, and the voltage is definitely LOW for both PLAY and PAUSE functions.PLAY voltage reads 1.04VDC. PAUSE voltage is identical.
It's as if PLAY and PAUSE functions have merged and are now the EXACT same PAUSE function, with a complete loss of PLAY function.
Adjusting VR401 (the Play mode voltage adjuster) does nothing. A preliminary check of all related transistors and diodes on the logic board has produced no clues. Everything checks out OK.
I am starting to suspect op amp 4558C (IC405), but am not sure how to proceed.
SOME INFO: The Play and Pause modes both involve negative DC voltages. The 10k "volume" pot previously mentioned is an internal motor- driven pot that gets voltages directly from the deck's logic board. This pot SHOULD be getting slightly less than 3VDC in PLAY mode, but instead gets just over 1VDC.
Here is the service manual:
What should I be checking that I haven't checked already?
Any help with this "tough dog" will be most appreciated.