Advice on repairing Radio Transmitter - Page 1
Forum section: electronics / repair

author: Amcv495
author_rank: Newbie
timestamp: September 30, 2023, 09:00:07 am
content: I am having an issue with a radio transmitter, when power is on, everything else is working except the LCD. I've replaced the screen however I've had no luck with the new screen either. I'm thinking there must be an issue with power supply to the screen but I'm not sure how to test it. The only thing i can see is a capacitor which is slightly discoloured compared to the rest but I don't know if this has any effect.I have some basic circuit knowledge and a multimeter - would anyone have any advice on the best way forward?

author: Shonky
author_rank: Frequent Contributor
timestamp: September 30, 2023, 09:05:22 am
content: Measure 3V3 to GND on the debug header with the meter on DC volts.If you have USB to UART module I'd listen on TX line and see if the CPU is spitting anything out. NB: nothing doesn't necessarily mean it's broken but if it is outputting it might provide some info and at least lets you know if the basics of the CPU are OK.

author: Amcv495
author_rank: Newbie
timestamp: September 30, 2023, 09:17:19 am
content: Thank you, I'll try that - I don't have anything to measure TX line but I'll put the multimeter over the GND and 3V3 and post the data.

author: MathWizard
author_rank: Super Contributor
timestamp: October 04, 2023, 07:37:44 am
content: Does the screen do anything at all? Does it light up at all ? You can look up all the chips and make sure they have Vcc.I'm guessing the big chip runs everything including the video, or maybe there's a smaller separate MCU that's the brains. Look up the chips coming from the ribbon cable, see if they are doing anything.Are there any chips or PCB on the actual LCD panel? You replaced the screen, but anything on there still could give some indication of what's wrong.I haven't had much luck with my old broken monitors, and I had to throw them out to save space.

author: Amcv495
author_rank: Newbie
timestamp: October 04, 2023, 07:52:22 am
content: I am fixing this for someone else and they had mentioned that the screen was flickering before it failed. No IC on the screen or mount, and that is the only chip related to the screen. There is another chip bit that's for the radio I think.What would be my best way of testing the connections from the chip? Is it a diode test. Makes things difficult without a schematic lol

author: Shonky
author_rank: Frequent Contributor
timestamp: October 04, 2023, 08:07:31 am
content: If the screen was flickering check the power supply. Have you done that yet? Is there a battery pack and another board somewhere?No a diode test is not what you you need to test connections and it's somewhat unlikely that has failed. Even then a visual inspection should give you a pretty good idea. You won't really be able to check continuity to the screen. Once it leaves the FFC (the connector) it's much harder to probe anything. You said you replaced the LCD anyway.

author: Amcv495
author_rank: Newbie
timestamp: October 04, 2023, 08:10:06 am
content: I thought it was the power supply, it is 8 AA batteries connected together with 2 fly leads. I will try it maybe with a Lipo battery. The LEDs and Buzzer are still working fine and all buttons seem to work. Just the screen is not

author: fzabkar
author_rank: Super Contributor
timestamp: October 04, 2023, 07:21:52 pm
content: FWIW, here is a datasheet for the Inanbo-T35C-ILI9488-V1 display:https://www.micros.com.pl/mediaserver/info-o%20tft-3.5tp-ips.pdfThe recommended supply voltage for the logic is 2.8V.The LED forward voltage is 3.2V, and there are 6 LEDs.This is the manufacturer's web site:http://www.inanbo.com/products.phpDatasheet for MCU:https://www.st.com/resource/en/datasheet/stm32f103rc.pdfhttps://www.st.com/resource/en/datasheet/stm32f103c8.pdfOther Inanbo datasheets:https://hadibanelectronic.com/wp-content/uploads/2022/03/INANBO-T28-ILI9325-ILI9328-V11.pdfhttp://aitendo3.sakura.ne.jp/aitendo_data/product_img/lcd/tft2/T43/INANBO-T43-V1.pdfhttp://manager3.dotname.kr/OHM_DATA/lE060408D/manual/T32-HX8347A-V12-ETC.pdf

author: Amcv495
author_rank: Newbie
timestamp: October 04, 2023, 07:33:04 pm
content: This is great thank you!

author: MathWizard
author_rank: Super Contributor
timestamp: October 05, 2023, 06:01:11 am
content: Ok so the big chip is a common MCU breed, can they actually be programmed to drive a small screen, or would they still need other chips for that ? I see a lot of traces going right to the ribbon cable, but IDK. Maybe there's no chips on the bottom of the PCB either.

author: Amcv495
author_rank: Newbie
timestamp: October 05, 2023, 06:05:40 am
content: Is there a way to test the chip and what's coming from it? (I have little to no knowledge of programming) I know UART module was mentioned above

author: Shonky
author_rank: Frequent Contributor
timestamp: October 05, 2023, 06:23:18 am
content: You could put a logic analyzer (or an oscilliscope) on the data lines. Unfortunately the display (if the datasheet linked is correct) is a parallel interface so means it's not as easy as it would be if was I2C/SPI/UARTMaybe it's the LED backlight only? You should be able to see if the display is doing something by shining a light at it.Measured the power supply yet? If you don't check the basics it's kind of pointless checking the more complicated bits.

author: Amcv495
author_rank: Newbie
timestamp: October 05, 2023, 06:31:34 am
content: I can't seem to see anything from the screen when I shine a light on it. I was expecting to see some sort of a line or something but nothing. But you're right I need to make sure the power supply is sufficient - I have no way to charge the power supply but taking someones word for it that it is fully charged. I'll put the multimeter over it this evening

author: Amcv495
author_rank: Newbie
timestamp: October 08, 2023, 09:51:43 am
content: Tested the battery and there is 10.5 Volts across it. Should be closer to 12V. But surely that is enough to power the LCD?

author: Shonky
author_rank: Frequent Contributor
timestamp: October 08, 2023, 11:07:27 am
content: See post #1. Measure 3.3VCheck power is on the LCD pins per the data sheet. Look for a cap nearby since the pads are small.