GD77 Not Powering On - Fixed

VK3KYY
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Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: GD77 Not Powering On - Fixed

Post by VK3KYY » Thu Sep 03, 2020 9:50 am

shanetrain wrote:
Wed Sep 02, 2020 7:34 am
Hi all.

Just thought i would share my issues with the GD77 not powering on.
Unit had something rattling around in it and radio would not power on.

After removing the main-board I found a small bit of solder floating around in the unit, this caused the issues.
Note - removing the GD77 main-board requires de-soldering the antenna connection, see attached picture.

I then discovered a little fuse on the board that had blown, (Littelfuse 3A FF Surface Mount Fuse, 32V ac/dc)
https://au.rs-online.com/web/p/non-rese ... s/5413619/

Replaced the fuse and the unit works again, hopefully this helps someone that has a non working unit.

De-solder the antenna connection image.
https://ibb.co/J37wbHB

Fuse location Image
https://ibb.co/GtStD2j
Very useful.

Thankyou

G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: GD77 Not Powering On - Fixed

Post by G4EML » Thu Sep 03, 2020 11:05 am

I purchased a non working GD77 from EBay for a low bid.

That also had a blown fuse but in my case it was caused by a short circuit capacitor on the board. Took a little while to find but since replacing it the radio has been working fine.

Colin G4EML.

G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: GD77 Not Powering On - Fixed

Post by G4EML » Mon May 17, 2021 8:51 pm

Another Ebay Purchase of a known faulty GD77 at a bargain price of £8 including postage.

The fuse was blown again but this time the short circuit was due to a burn-up of the audio amplifier chip. There was quite a lot of PCB damage underneath the chip including a short between the multilayer ground and power planes.
The chip was removed and the PCB was tidied up but the damage was too bad to reuse the pads.

I was unable to find a replacement LM4951 so I substituted an LM4861M which is a similar amplifier but needed an extra transistor to invert the mute signal.

I assembled the new amplifier 'Dead bug' style on the large ground plane area next to the original chip location and encapsulated it in UV setting resin. Not pretty, but it worked and the radio is now performing perfectly. (obviously with OpenGD77 loaded)

Overall, probably not a repair I would recommend to anyone else but it is quite satisfying to have resurrected a dead radio.

Colin G4EML

VK3KYY
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Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: GD77 Not Powering On - Fixed

Post by VK3KYY » Mon May 17, 2021 9:09 pm

Thanks Colin

I presume that radio could have been used as a hotspot even without replacing the audio amplifier chip

G4EML
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Joined: Sat Nov 16, 2019 10:01 am

Re: GD77 Not Powering On - Fixed

Post by G4EML » Mon May 17, 2021 9:14 pm

Once the amplifier chip was removed and the PCB short fixed it did work, you just couldn't hear anything. So yes, I assume it would have worked as a hotspot.

Colin.

VK3KYY
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Location: Melbourne, Australia

Re: GD77 Not Powering On - Fixed

Post by VK3KYY » Mon May 17, 2021 9:23 pm

G4EML wrote:
Mon May 17, 2021 9:14 pm
Once the amplifier chip was removed and the PCB short fixed it did work, you just couldn't hear anything. So yes, I assume it would have worked as a hotspot.

Colin.
OK. It would still be cheaper than buying a mmdmv hotspot board, albeit would only work for DMR audio

kt4lh
Posts: 272
Joined: Sun Jan 12, 2020 4:27 am

Re: GD77 Not Powering On - Fixed

Post by kt4lh » Sat Oct 08, 2022 11:55 am

kitt1977 wrote:
Fri Oct 07, 2022 2:59 pm
G4EML wrote:
Thu Sep 03, 2020 11:05 am
I purchased a non working GD77 from EBay for a low bid.

That also had a blown fuse but in my case it was caused by a short circuit capacitor on the board. Took a little while to find but since replacing it the radio has been working fine.

Colin G4EML.
Do you remember what cap ? Can't seem to find one power rail has a short Removed ic and capacitor close to it .. short stays ..
If your meter is pretty good you can sometimes find or localize a short by looking at everywhere the short shows up and finding the lowest resistance. But this may not work on a small PCB, I've seen this technique used on motherboards etc.

W7OBB
Posts: 14
Joined: Tue Jan 04, 2022 7:24 pm

Re: GD77 Not Powering On - Fixed

Post by W7OBB » Tue Jan 30, 2024 3:59 am

I tried to add the GP-02 GPS module to my GD77 for APRS and I must have caused a short. I checked the fuse and it had continuity end to end so I assume that means it is still good?

As you can probably tell, I'm new to pcb troubleshooting. Any further suggestions to find the short or fix my radio?

VK3KYY
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Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: GD77 Not Powering On - Fixed

Post by VK3KYY » Tue Jan 30, 2024 4:26 am

W7OBB wrote:
Tue Jan 30, 2024 3:59 am
I tried to add the GP-02 GPS module to my GD77 for APRS and I must have caused a short. I checked the fuse and it had continuity end to end so I assume that means it is still good?

As you can probably tell, I'm new to pcb troubleshooting. Any further suggestions to find the short or fix my radio?
Check for 3.3V on the flash chip etc

Possibly you blew the 3.3V regulator

W7OBB
Posts: 14
Joined: Tue Jan 04, 2022 7:24 pm

Re: GD77 Not Powering On - Fixed

Post by W7OBB » Tue Jan 30, 2024 1:30 pm

Complete newb here so please forgive my dumb questions.

Is there a electrical/pcb diagram somewhere online to help me find components?

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