Negative power supply give positive output (bob 5 Jye120)

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onalone2000
Posts: 5
Joined: Mon Jul 30, 2018 11:57 pm

Negative power supply give positive output (bob 5 Jye120)

Post by onalone2000 »

Dear JYE,

I have a problem with the kit. I have passed the power test 1. The LCD on ok and can adjust the encoder and see the menu.

Power at +5V is ok, but the V- is around 0.68V. AV+ is ok, around 5V. I check the polarity of C27 and it is fine. I measure the power in Bob5, at pin 8 have power. Indirect measure of pin 2 at the diod size is 0V.

Do you have any suggestion to check further ?

Best wishes,
Trinh Hoai Thanh
onalone2000
Posts: 5
Joined: Mon Jul 30, 2018 11:57 pm

Re: Negative power supply give positive output (bob 5 Jye120

Post by onalone2000 »

I am waiting for the support on the DSO 068.

According to the powering-up test 2, the Bob 5 board or C27 issue. And I found that there is output at the output of BOB5 board.

So they issue comes from the faulty of BOB5 board.

Attachment is for your reference.

Look forward to the suggestion.
Attachments
Voltage at V-
Voltage at V-
onalone2000
Posts: 5
Joined: Mon Jul 30, 2018 11:57 pm

Re: Negative power supply give positive output (bob 5 Jye120

Post by onalone2000 »

I removed BOB 5 board and supply 5+ power to BOB5, the out put voltage is 0.23V. It means that BOB 5 is faulty.

I de-soldered the C35 (in JYE 120) and checked, it is ok.
The diod D8 1N5819 seems ok.
C38 is ok.

The suspect component is U7, MC34063.
onalone2000
Posts: 5
Joined: Mon Jul 30, 2018 11:57 pm

Re: Negative power supply give positive output (bob 5 Jye120

Post by onalone2000 »

As per identified, the BOB5 JYE120 is malfunctioning.

While waiting for the BOB5 board, I used a temporary -5V source and the DSO068 work fine.

The picture is after calibration. I am not sure whether it is good or not because there was not much change in the wave form.
IMG_20180820_181918.jpg
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