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Mar 10, 2018, 09:51 AM
Hot glue will fix anything!
Uksteve's Avatar
Help!

Anyone know about electronics?


Hi, i have a dead 5.8ghz amplifier, it worked for all of 2 mins then the power led extinguished and the current draw went from the 2A normal pull when transmitting to drawing 1.4A regardless of input signal, and no longer transmits at all.

There is still a passthrough for the connected vtx.

certain components get very hot very fast, im not an expert on electronics but the grey box is an inductor? this gets uber hot in an instant, i know they get hot but this seems extreme , like theres a short?

next to it is a black oblong component with a terminal at each end, i have no idea what this is but it also gets very hot , as does the IC that lives next to them both.

further up the board, one of the IC's that i belive to be the outputs gets very hot but its twin opposite does not even get warm.

the circuit is pretty simple, as are most linear amplifiers, theres nothing on the other side of the pcb apart from traces to the led , fan and power input socket, absolutely everything important is contained on this side of the board.

I have good enough soldering skills to replace anything on the board apart from the outputs, those were clearly re flow mounted where is many other components were obviously hand soldered looking at the work.

I have a replacement being sent to me but if from the pictures and my description of the symptoms someone can point to a possible fix, id give it a go, its worth a try!

in my second image of the whole pcb, it is possible to see all the traces that are visible to the eye , it looks like a multi layer board, possibly traces under the heatsink on the other side but its stuck down very well , i removed the screws and tried to take it off for a peek but its stuck fast and ill likely damage the pcb trying to get it off.

the heatsink is totally flush with the pcb, theres definitely nothing under it apart from the pcb.

thanks in advance, steve.
Last edited by Uksteve; Mar 10, 2018 at 10:42 AM.
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Mar 10, 2018, 11:41 AM
Registered User
HI Steve,

Since your power supply components are getting hot also one of the output drivers, I would take a gamble and desolder the vcc pin of the hot ouput device and then see if the PSU components then run cool.

The SS54 is a Schotky diode, that is easy to check with a multimeter but it is always best to desolder and check these out of the circuit as you may be also measuring other in circuit resistances, it should be high resistance one way and low the other, easier if you have a diode test mode on your meter.

My thinking is that the hot SE5004L amp is goosed and is loading up the PSU making those components hot, the SE5004L can be changed if you have a small enough soldering iron or are good with a hot air gun and solder paste, at work I use a dremel cutting disk to cut through the legs around the chip and when the chip body is removed the legs can easily be lifted off using a fine tipped iron.

The small 5 pin chip is your 3.3v regulator.
Last edited by NOGPS; Mar 10, 2018 at 12:52 PM.
Mar 10, 2018, 02:28 PM
Hot glue will fix anything!
Uksteve's Avatar
Quote:
Originally Posted by NOGPS
HI Steve,

Since your power supply components are getting hot also one of the output drivers, I would take a gamble and desolder the vcc pin of the hot ouput device and then see if the PSU components then run cool.

The SS54 is a Schotky diode, that is easy to check with a multimeter but it is always best to desolder and check these out of the circuit as you may be also measuring other in circuit resistances, it should be high resistance one way and low the other, easier if you have a diode test mode on your meter.

My thinking is that the hot SE5004L amp is goosed and is loading up the PSU making those components hot, the SE5004L can be changed if you have a small enough soldering iron or are good with a hot air gun and solder paste, at work I use a dremel cutting disk to cut through the legs around the chip and when the chip body is removed the legs can easily be lifted off using a fine tipped iron.

The small 5 pin chip is your 3.3v regulator.
thanks for your reply, ive looked at the data sheet for the output, in my image ive put an arrow on pin 18 (vcc3) it seems to be the one that feeds the ic, ive put a line where i would cut the trace to kill the power, your thoughts?.

steve.
Mar 10, 2018, 02:47 PM
Hot glue will fix anything!
Uksteve's Avatar
hmmm, its definitely the output, cut power to it (sort of) the led started blinking (meant to be solid) and the power circuit ran cool but the ic was still getting power from somewhere.

run it with an input attached and the other side is getting hot and the power circuit running hot again.

i think something is wrong further in from the outputs that is not regulating properly and allowing the outputs to run away with themselves?

The other possibility is that this is rated to accept a 600mw input but that this is a Chinese rating rather than a real one and they have been over driven by the input
Mar 10, 2018, 02:52 PM
Hot glue will fix anything!
Uksteve's Avatar
i know with amplifiers that theres a limit to how much power you can drive them from, they are linear amplifiers (sort of) and output increases with input but theres a limit.

for example the amplifier is use on my 27mhz cb can be driven from a max of 16w and i have to turn down my rf power when using it to avoid the magic smoke

i think these cant handle the 600mw they are rated for, im gonna be limiting to 400mw when i get the new one i think, maybe even 200mw!
Mar 10, 2018, 03:03 PM
Hot glue will fix anything!
Uksteve's Avatar
double hmmm, according to the data sheet max input is just under 4mw and max output for each is just under 800mw but then says output with no modulation is 2.5w

ive got lost in the specs ha ha
Mar 10, 2018, 03:11 PM
Registered User
There are three stages of amplification in these chips, each has its own VCC pin, the other chip may be getting hot now as it is trying to do all the work also the circuit will be out of balance with the bad one disconnected, some of the input circuitry is to balance and split the input evenly to both chips.

I am puzzled about the yellow label on your cover, it seems to indicate this thing can do 2.4g band as well as 5.8, is that some kind of chinglish translation cock up ?
Mar 10, 2018, 03:19 PM
Registered User
Running the circuit with no rf input and check the dc voltages incuding vref might verify if the psu and regulation circuitry is ok, i doubt if you wll do permanent damage to the psu as it has good current limit protection built in, thats why you see the current drop and not rise when you have a fault condition. The led blinking is possibly the psu current limit pulsing.
Last edited by NOGPS; Mar 10, 2018 at 03:24 PM.
Mar 10, 2018, 03:43 PM
Hot glue will fix anything!
Uksteve's Avatar
Quote:
Originally Posted by NOGPS
There are three stages of amplification in these chips, each has its own VCC pin, the other chip may be getting hot now as it is trying to do all the work also the circuit will be out of balance with the bad one disconnected, some of the input circuitry is to balance and split the input evenly to both chips.

I am puzzled about the yellow label on your cover, it seems to indicate this thing can do 2.4g band as well as 5.8, is that some kind of chinglish translation cock up ?
Only just realized who you are, hi lol.

yeah, its chinglish, the data sheet says 5.8 and the seller (banggood) states it as being for 5-6ghz and also states its not compatible with wireless routers, guess thats there loose way of saying not for 2.4ghz lol

this is the link to the product

https://www.banggood.com/Signal-Enha...48507252016052
Mar 10, 2018, 03:49 PM
Registered User
Apart from the satisfaction of repairing it I can't see why you would as a new one costs so little , the chips are 4.00 each plus vat and then postage on top.

I would repair it but thats me I hate to be beaten by a problem, I fix things at work others would put in the skip but you don't learn much chucking stuff in the skip.
Mar 12, 2018, 12:07 PM
400' ..... NOT
Martin Y's Avatar
You did have it connected to an antenna or dummy load and something( like a shunt) on the input before powering it up? That is one big amp for 5.8 as just turning on at home would interfere with 5.8 wifi's near by. Unless you have a hot air rework station repairing won't be easy.
Mar 13, 2018, 01:24 PM
Hot glue will fix anything!
Uksteve's Avatar
Quote:
Originally Posted by NOGPS
Apart from the satisfaction of repairing it I can't see why you would as a new one costs so little , the chips are 4.00 each plus vat and then postage on top.

I would repair it but thats me I hate to be beaten by a problem, I fix things at work others would put in the skip but you don't learn much chucking stuff in the skip.
yeah your right, economically is not really worth the effort but just like you, i get a lot out of beating something but this time i think im going to accept that its just not worth it.

from the specs of the chips and what you have seen of the module do you think that the input power could have been the cause, do you think the chip fried from being over driven?

the unit is rated for up to 600mw input and thats what i hooked up, infact i used the exact same vtx as they picture in there page, i didint go out and buy it specially, i just happened to have one and that is what was kicking around spare for testing.

id like to run it at its full capacity but if running 600mw into it is going to risk blowing the replacement i can live with driving it from 200 or 400mw.

whilst im here, can i ask a question relating to current flow/ video outputs.

i have a new pair of box goggles, they are very good (should be considering how much they cost!) they have a 7" screen, a resolution of 1280x800 (i know standard fpv systems dont use a resolution this high) and has composite in/out and hdmi in.

where im not 100% is on the composite in/out.

both share the same line, when in the main internal receiver mode, the composite in/out is an output but when in AV IN the same line becomes an input.

Although these goggles already have a built in true receiver diversity setup, im going to be using a PRO58 Fatshark module on the goggles for a number of reasons.

the PRO58 provides a very slightly better image, the difference is very small but the image is brighter and the tiniest but sharper.

i also want to make use of all the better functions these modules have with the custom firmware and lastly, piodabro is working on a true OSD overlay for the PRO58 and if hes successful we will get on screen info (signal strength ect) and menu navigation on screen whilst the video is still present.

My question is whats the long term affects of two devices outputting composite video outputs face to face?

I know in the sort term theres no damage but im not 100% on it happening over and over.

the goggles always start in receiver mode and have to be switched to AV in, the receiver is incorporated to the screen processing unit board and cannot be deactivated.

Id like to just have the fatshark module wired to power up with the rest of it but if theres an issue with the two outputs , i would fit a kill switch the the av line to block it til i have switched modes.

i thoughts on the lines are this.

1- the levels on the lines are too low to cause damage.

2- dont laugh at me if i have this wrong but the two are not reversed polarity, composite + to + and - to - would cause a no flow scenario instead of one driving into the other?
Mar 13, 2018, 02:03 PM
Registered User
HI Steve,

As you probably know composite video is usualy 1v Peak to peak into a 75 ohm load, as a safeguard I would not switch on your external rx till you have switched the goggles to AV in , its a pain but better to be safe than risk damaging either device.

Having two video devices outputing into the same point would not usualy cause a problem but best to be safe as you don't know how protected the switching logic is in the goggles.
Mar 13, 2018, 02:14 PM
Hot glue will fix anything!
Uksteve's Avatar
Quote:
Originally Posted by NOGPS
HI Steve,

As you probably know composite video is usualy 1v Peak to peak into a 75 ohm load, as a safeguard I would not switch on your external rx till you have switched the goggles to AV in , its a pain but better to be safe than risk damaging either device.

Having two video devices outputing into the same point would not usualy cause a problem but best to be safe as you don't know how protected the switching logic is in the goggles.
ok, its so frustrating that the goggles revert to a default of internal receiver each time they are turned on.

im sure it must have been more complicated for the manufacturer to create a one line in/out switched circuit than it would have been to just feed them out as separate lines!

1v usually, except for in my car, running 4v lines in my system
Mar 13, 2018, 02:19 PM
Registered User
My car av system has unconventional video input and output levels too.


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