开云体育

Well, my newly assembled QDX high band version ran great for several hours but I managed to give it the opportunity to let the smoke escape from Q9 - cracked it in half. Man, that stuff stinks! :-(

So, I probably ought to replace all four of the final PA guys while I'm at it. But, are there any tests I can do with or without them on the board to see if anything else retired early? I'd hate to un-solder those four little things, put in new ones, only to have them blow up again after the next power-up.
--
Jim / K7TXA
Eagle, ID

SKCC 10447
BUG 301

Hi Jim,

Sorry to read that the smoke escaped.? Before putting new BS170s in place, I would verify that the current draw when receiving is about 150ma, that the receiver is working, and test IC5 using the terminal transmitter test program.? You can use an oscilloscope to verify a 5-volt square wave on the 4 gate pads of the BS170s.? If you do not have a scope, you can use a DMM to measure the gate voltages when receiving (0) and transmitting (2.5 volts).?

If all of the above checks out, then install the new BS170s.? I would suggest replacing all of them if any have tested as bad.

73
Evan
AC9TU

Hi Evan -

Thanks for the reply to my message a few days ago - sorry for the delay in responding; today I just got a couple packs of the BS170s in the mail. I used my de-soldering tool to clean out the 12 holes in the board, so that's taken care of. Tonight I hooked up a 9v power supply, antenna, and my USB cable. Turned on the QDX and then fired up WSJT-X on 20 meters. The radio seems to be receiving very well, so that's at least one good thing. I do notice that IC2 (voltage regulator) and IC5 get pretty warm just on receive. My power supply is reporting a current draw of 145ma on receive.

I'm hesitant to try going into transmit until someone tells me that having those two ICs get warm is an OK thing.

I do have an o-scope and while far from being an expert with it, I can probably figure out which pads are the gates of the BS170s. Rookie question - will that 5v square wave be there on receive, or only on transmit?

I've never used the terminal programs for the QDX rig so that might be a steep learning curve. :-( In fact, I'm using a Mac Mini and I'm pretty sure that Putty is not even installed at this point.
--
Jim / K7TXA
Eagle, ID

SKCC 10447
BUG 301

What is "pretty warm"?

Cannot touch, burns?
I feel heat but I can touch it for extended time?

Anything up to about 120F is not a problem.

Note some power supplies on turn on can spike a voltage higher than 9V.
That can be hard on parts.

--
Allison
------------------
Post online only, please no email.

Hi Jim,

You do not need to use the terminal program to test IC5.? The terminal program eliminates any PC audio issues when transmitting.? Instead, you can use the Tune feature in WSJT-X to transmit.? Be sure to leave the BS170s out until you have verified IC5 is working.

IC2 being warm is OK, as long as not too hot to keep your finger on it.? IC5 should not be warm.? IC5 generating heat when receiving is one indication that it is fried.? The best test is to test for the squarewave when transmitting and 0 volts when receiving.??The gate pads are the center pins of each of the BS170s.?

If you do have to replace IC5, there are three methods:?
1 - Use a hot air rework tool (the preferred for me)
2 - Use a low-temperature solder like ChipQuick to heat all pins simultaneously to remove the IC.
3 - Use a very fine point diagonal cutter to clip each of the leads of IC5.

Method 1 is the most expensive tool but can be used many times:

or

My station is not offered on Amazon anymore, and it was more expensive than the two above.? The second rework station might be better if you do not have a fine-point soldering iron.

The issue with choices 2 and 3 is the cleanup of the board after the IC is removed.? I damaged a board when using a solder wick to clean off the excess solder after cutting out IC5.?

I suggest you search YouTube for videos on SMD replacements for your chosen tool.


In my experience, there is a better than 50% chance that IC5 is bad when one or more BS170s fail.
73
Evan
AC9TU

It appears that IC5 has gone to the happy hunting ground. After 30 seconds of receiving, it is far too hot to touch, AND there is no voltage on the gate of any of the final pads. I've ordered a five pack of them and expect delivery some time next week. Also ordered a hot air rework tool for easier removal of the bad IC5. Interestingly the one I had ordered the other day was the one you put a link to as option #1.

So, I'll go back to using my low-band QDX for a while, along with building the EMTECH ZM-2 tuner kit I've had lying around for a few weeks.

73 - thanks for the help. I'll report back after the IC5 replacement is installed.
--
Jim / K7TXA
Eagle, ID

SKCC 10447
BUG 301