Hitachi TRK 8190 - no stereo reception in FM

[beamrider]

So now I've socketed both chips.

Without anything in place I'm reading 6V from Pin (1) - VCC of IC301 (BA1330 MPX) socket, however when I socket the replacement chip it still drops down to 3v at pin 1 whereas I believe it should be ~6V for the chip to operate correctly. Puzzled again.

 

[beamrider]

OK, so today I swapped Q502 and the voltage rail came up to 5.7V with the FM stereo light back on. Thanks for help!

 

[Tinman]

Took a while but that's great you got it up and running.

 

[beamrider]

So after putting fitting new belts and putting the cassette deck back. It has now developed another fault. When playing a tape or switching to the radio, the audio immediately fades away as though the power has been switched off. I must have damaged it somehow...

 

[hopey]

So after putting fitting new belts and putting the cassette deck back. It has now developed another fault. When playing a tape or switching to the radio, the audio immediately fades away as though the power has been switched off. I must have damaged it somehow...

Is it just the tape Deck Audio? Could be the op amp caps for the Tape heads to line level.

 

[beamrider]

Is it just the tape Deck Audio? Could be the op amp caps for the Tape heads to line level.

No, happens on radio. When you switch the input selector from tape to radio, you get a burst of audio that quickly fades away distorting as it does so.

 

[hopey]

No, happens on radio. When you switch the input selector from tape to radio, you get a burst of audio that quickly fades away distorting as it does so.

Might be the sleep function try press play on the tape and switch function to radio.

 

[stereomann]

maybe a dirty switch. when you press play on the deck does it power up the unit?

 

[beamrider]

Thanks for the suggestions. It occurs on both tape and radio i.e. only brief decaying audio. Tape motors function normally. Timer switch is not on. I don't think it's dirt related as it was working one minute and faulty the next. Is there supposed to be some insulation between the rear of the cassette mechanism and the main board, I wondered if I shorted something out when refitting? One other piece of information, prior to it failing I noticed a kind of popping sound that seemed to get worse when the EQ or Bias switch was altered and the LEDs were flickering with no sound output.

 

[hopey]

Could be faulty Potentiometer.

 

[beamrider]

So I made some progress - replaced Q502 again. I think I hadn't made a good enough heatsink and it had overheated. Now the radio and cassette are working again, but when cassette is in stop mode, the motor still runs and a clicking noise is head from the speaker. The noise is muted by engaging the tuning/battery light switch.

New video by Adrian Fox

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[beamrider]

Is it normal for the motor to be spinning when in cassette stopped mode on this unit?

 

[Tinman]

Is it normal for the motor to be spinning when in cassette stopped mode on this unit?

Never had one of these but I'd guess no.
Possible leaf switch making contact when it shouldn't?

 

[hopey]

there could be stray injection you should reassemble to ensure all the grounding is correct.

 

[beamrider]

Thanks for suggestions. I find this unit quite challenging to work on due to various fragile cables to the cassette mechanism from the main board - not sure why they didn't put it on a connector block(s) like they have done for the tuner board.

 

[Superduper]

The motor boating sound from speakers is usually from poor connections or failing capacitors. My money is on connections being poor. Try cleaning the crap out of the record-playback switch. Since your chassis is out of the cabinet, it’s rather easy to access the record bar. Spray the ends of the bar with deoxit or equivalent and work the switch manually many times, let it dry and retest. All switches should be cleaned as well.

 

[Superduper]

Oh and the motor should not be running in stop mode. The play switch (not the key) is probably triggered. Maybe a hanging wire or something is pushing down on the leaf (these switches are usually open exposed leaf switches).

 

[beamrider]

So the saga continues..

I briefly grounded the negative motor terminal and afterwards the tape started working properly - no motor turning in
stop mode. Now plays cassettes fine...BUT the radio is broken again. It's reverted to the briefly decaying sound.

 

[Tinman]

So the saga continues..

I briefly grounded the negative motor terminal and afterwards the tape started working properly - no motor turning in
stop mode. Now plays cassettes fine...BUT the radio is broken again. It's reverted to the briefly decaying sound.

I might be confused but it doesn't sound right that grounding the negative side of the motor has it working properly.
The negative side has to be grounded for the motor to work in the first place and you said it was spinning in stop mode.
For that to happen, there has to be power provided to the motor in stop mode when there shouldn't be and the negative side has to be grounded.

 

[beamrider]

Thanks for replies.

Yes I am confused too. But that is what happened, when I touched the black motor wire to ground as I was looking for stray injections I heard a small pop and then the cassette side of things started working correctly. I was dismayed when I discovered the radio broken as a consequence.

Will take a little break from it and regroup my thoughts. Seems every time I think it's fixed another problem develops. Guess I'm out of my depth really but this is just a hobby so will persevere when the annoyance levels subside.