Akai GX365 - UK Vintage Radio Repair and Restoration Discussion Forum

Michael Maurice · 28th Jul 2016, 3:46 pm

The problem with the above deck is that I cant set the bias on the RH channel (tracks 2-3)

The high frequencies are far too high and no adjustment of the bias can reduce it.

I've scoped the output of the bias pots. On CH1 there is a good range of bias control, on CH2, not so.

I swapped the record amplifiers but that made no difference.

The pot and the associated resistor are within spec.

Which leaves one thing, the record head or possibly the erase head. Can anyone concur or if you think of another cause then let me know

Marconi_MPT4 · 29th Jul 2016, 12:04 am

Hi,
Between the bias oscillator output board and the record head is relay R401 on the track selector board. On a few occasions have had to clean the contacts, or replace relay in severe cases. Also the bias appears to be routed through track selector switch which may have an open circuit. In both instances no head load gives high output with little or no adjustment level.

Try swapping over the bias output connections on pins 8 and 9 of the bias oscillator board to help confirm location of fault.

Rich

radiotechnician · 3rd Aug 2016, 9:24 am

The output of right channel rec amp board (pin 2) goes to a 5.6 mH coil L401

which is in parallel with a 470 pFd capacitor. These are on the track selector

board. This circuit passes the audio from the rec amp to the head, but blocks

the bias from flowing back to the rec amp. If the 470 pFd was shorted, or L401

was open, bias would be shunted to ground with the trap inoperative.

Insets from pages 117, 120 and 123 Akai Schematic Register Sect 0.

28th Jul 2016, 3:46 pm	#1
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,224	Akai GX365 The problem with the above deck is that I cant set the bias on the RH channel (tracks 2-3) The high frequencies are far too high and no adjustment of the bias can reduce it. I've scoped the output of the bias pots. On CH1 there is a good range of bias control, on CH2, not so. I swapped the record amplifiers but that made no difference. The pot and the associated resistor are within spec. Which leaves one thing, the record head or possibly the erase head. Can anyone concur or if you think of another cause then let me know __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

29th Jul 2016, 12:04 am	#2
Marconi_MPT4 Heptode Join Date: Mar 2011 Location: Dorset, UK. Posts: 521	Re: Akai GX365 Hi, Between the bias oscillator output board and the record head is relay R401 on the track selector board. On a few occasions have had to clean the contacts, or replace relay in severe cases. Also the bias appears to be routed through track selector switch which may have an open circuit. In both instances no head load gives high output with little or no adjustment level. Try swapping over the bias output connections on pins 8 and 9 of the bias oscillator board to help confirm location of fault. Rich __________________ To an optimist a glass is half full; a pessimist half empty; an engineer twice as big as need be!

3rd Aug 2016, 9:24 am	#3
radiotechnician Pentode Join Date: Jan 2013 Location: Powell River, British Columbia, Canada. Posts: 217	Re: Akai GX365 The output of right channel rec amp board (pin 2) goes to a 5.6 mH coil L401 which is in parallel with a 470 pFd capacitor. These are on the track selector board. This circuit passes the audio from the rec amp to the head, but blocks the bias from flowing back to the rec amp. If the 470 pFd was shorted, or L401 was open, bias would be shunted to ground with the trap inoperative. Insets from pages 117, 120 and 123 Akai Schematic Register Sect 0. Attached Thumbnails __________________ Steve Dow VE7ASO