Sanyo M6900 Boombox problem

I am trying to restore an old Sanyo M6900 and everything seems to work fine but the set gives the distortion at high volumes. Specially at lower frequencies of the audio frequency bandwidth (20Hz - 20Khz). M6900 works between (100Hz - 8khz) audio frequency bandwidth. I tried everything. Checked voltages and even replaced a new power transformer and the filter capacitor but the distortion at high volumes problem still persists. I dont have anything else to try.
I conclude that every M6900 power amplifier is designed this way and we cant do anything about it. Distortion at high volumes is the feature of the power amplifier design (TA7769) and nothing could be done about it. Power Amplifier is designed around TA7769 Chip and the preamplifier section is around BA3306 chip. Set works at 7.5Volts DC. Uses 5 batteries 1.5volts each.
I dont have the service manual for M6900. Will appreciate if somebody could provide.
Please, Help somebody.

noddy55 said:

I am trying to restore an old Sanyo M6900 and everything seems to work fine but the set gives the distortion at high volumes. Specially at lower frequencies of the audio frequency bandwidth (20Hz - 20Khz). M6900 works between (100Hz - 8khz) audio frequency bandwidth. I tried everything. Checked voltages and even replaced a new power transformer and the filter capacitor but the distortion at high volumes problem still persists. I dont have anything else to try.
I conclude that every M6900 power amplifier is designed this way and we cant do anything about it. Distortion at high volumes is the feature of the power amplifier design (TA7769) and nothing could be done about it. Power Amplifier is designed around TA7769 Chip and the preamplifier section is around BA3306 chip. Set works at 7.5Volts DC. Uses 5 batteries 1.5volts each.
I dont have the service manual for M6900. Will appreciate if somebody could provide.
Please, Help somebody.

Click to expand...

Have you tried plugging in headphones I left you post about manual on your other thread

Thanks! for the reply,
Yes i tried the headphone as well. It was a 32 ohm impedance headphone. Aiwa brand.

Problem, is similar with the headphones also. Distortion at high volumes. So, this is nothing to do with the speakers of the set.
Speakers are fine and the original ones 3 ohm impedance.

I have also installed the new dc motor from mitsumi, the reason behind being is the thought that the old motor might have been consuming more current than needed. Power transformer is 500 milli ampere rating. Problem persists even with the 1 Amp rating transformer also.

I have also changed the Pre-amplifier filter capacitor(1000MFD/16v) at pin number 6 of BA3306 as well as the power filter capacitor(2200MFD/16V). I have checked each and every component of the preamplifier regulated power supply, also (C1815, 220ohms resistance, 6vZener, 220MFD/10v). Changed the spike filter(220MFD/16V) of power amplifier.

I have also changed the four bridge rectifier doide(IN4007 along with .01MFD capacitors).

Sometimes the voltage, is too high in our locality. So, the output rectified dc voltage goes up to 14volts, specially at nights. I am littlebit afraid of 6V dc motor working at 14 volts. Will this do any harm to dc motor or is it fine? The old motor was working with the same rating, just fine.

Do i really need to do something about the DC Voltage? Only the power supply for preamplifier is regulated(around 5 volts).

I tried to install the new voltage regulator with LM317 for the whole set but the same problem still persists even with the fully regulated power supply.

I did not found the datasheet for TA7769(power amplifier) in English. BA3306(pre amplifier) datasheet is available, easily.

What else to do?