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Author Topic: G7000 Power Supply FAILURE  (Read 2119 times)
AXEL72
Trying to get the cartridge in...
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Posts: 3


« on: January 31, 2018, 10:10:03 AM »

HI ALL !!!

I'm a new member of this community, i'm from Italy.
I own a G7000 since 1981 it worked well untill i think to add an interruptor on the 5v line between the internal power supply and the Mother Board.

It worked for 3 or 4 times,then the power supply starts to make an alternate and regular "buzz" and the console startup with sounds and blinking video.

NOW....the Mother board works well because i tried to supply it with a stabilyzed external Power and it starts normally BUT the power supply (with a tester attached on 5v and disconnected from the PCB) seems to INCREASE the voltage every "buzz" and it grows and grows...i stopped it disconnecting the 220v at 10v...

Someone knows what can be happened ?? and what can i do to fix it ? i thinked about the Transistor BUX84 or the Chip TDA2581. Some suggestions ?

Many thanks to all !!!
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gertk
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« Reply #1 on: January 31, 2018, 06:20:26 PM »

Most switch mode power supplies don't like to run without load, so put a suitable switch in the mains connection and not in the 5 Volt circuit.
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>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
AXEL72
Trying to get the cartridge in...
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Posts: 3


« Reply #2 on: February 01, 2018, 10:34:42 AM »

Most switch mode power supplies don't like to run without load, so put a suitable switch in the mains connection and not in the 5 Volt circuit.

Exactly what I had thought.

can anyone suggest what could have broken?
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gertk
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« Reply #3 on: February 01, 2018, 07:27:20 PM »

Maybe something in the output voltage feedback circuit got damaged (optocoupler maybe).
I do not have the circuit of your type of power supply at hand, and my G7000 has a simple linear power supply.

Can you post a picture of your power supply ?

 
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>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
AXEL72
Trying to get the cartridge in...
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Posts: 3


« Reply #4 on: February 02, 2018, 04:44:34 PM »

Attached a picture and the schematics (don't know if it's exactly the same model)

Many thanks
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gertk
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« Reply #5 on: February 03, 2018, 06:48:20 PM »

Ah, this type of power supply dos not have a feedback from the output, instead it uses a voltage from the primary side of the transformer as feedback (14V through D192). No wonder the output is going up without a load.

But now on what could have been damaged, you need to measure the output diodes D193 and D194 for short circuit, check the fuse VL215 also.  If you do not have experience in repairing 'switch mode power supplies' (SMPS)  I suggest removing the whole power supply board and use a modern external adapter which can deliver a stable 5V at 1 or 2 Amps.
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>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
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