Hi Peterr, As i own one of these i am gald to see your work on it. Saving this video for future utire reference. I habe read about some of thebither failuers on these as you mention but if you get a chance to do another lesson reharding any of those faluures ,it would be appreciated for sure. 73 Jim
So, I have a 125b with the same problem. However, my board in the amp is never. I have version 1.041. This means they have changed the power circuitry (a little bit) and removed all component markings from the PCB (thanks, it really helps to repair things…). Clearly, they don't want you in the box. I think I have the problem located, but if anyone has done this on a 1.041 board, I replaced what I believe your suspect MOSFET and Diode were. Now I may have done the wrong parts as all component markings are now gone. Still not working... @Peter, I would love some advice!
A brilliant video and good investigation, but what went wrong with the world?!? Why don't we have proper power switches any more so we can turn things off off and not just a "standby" mode 😢
Great diagnosis, however replacing the burned component with the same type and not finding out WHY it failed in the first place is like replacing a fuse. I try to locate the fault that caused the component failure, otherwise the unit will soon be back for the same repair in my shop and it will usually be under my repair warranty. I spotted no thermal grease on the varistor on top of one of the finals in this video. 10:48 That tells me that the bias is probably not tracking properly.
Thank you. I agree, but you do not find always a reason for a fail, you should know that. In this case, we assume a failing part by normal selection in the first half year after taking the unit into service. We all know that this is consumer electronics, and vendors don't buy parts which were running through a binning process for a lot of money. Bias don't get tracked in this design. We have a fixed Bias level for MOS FET's. The varistor is taking the environment temperature and it is an adjustment question only to track the temperature.
The Chinese radios never have any surge protection on the input so all that fancy complicated power switching circuitry is easily damaged by spikes on the power source. I wonder why they don't just use a simple On/Off switch?
Very easy, follow my explanations. What you see is the reaction of pushing the on/ off button and the MCU which is switching off. That is consequently the collector voltage at the digital transistor.
it's planned obsolescence probably. A stronger MOS is needed there to reliably switch the power. Also, the thermistor is not touching and lacks thermal compound to that final MOS RD100HHF1C, resulting in bad thermal compensation.
No, it is not a stronger MOS FET needed. If you watch the current capability of this part, you know that it is only a fraction of its capability which this FET has to handle.
@@TRXLab that is absolutely true, in normal operating conditions. But at startup, when all the electrolytics on board are empty, the switched current is brutally high for a few microseconds. It's enough to overstress the junction of that switching MOS.
Do not buy a Xiegu XPA125B or any Xiegu product! This amplifier was originally introduced with a good design using a pair of RD100HHF MOSFETs to easily handle 100W. After a few years they started selling units using a single AFT05MP075N rated for 75W without any change to published specifications. You can push these amps to 75-80W but they are now really a 50W nominal amplifier to achieve the same IMD rating. For a company to engage in these unethical design practices, I'd strongly recommend to never buy any Xiegu products! This is the same practice that Huawei tried when they started to gain some market share in the US with their phones and tablets.
