Image: The "Red Ferrari" uBitx V3 HF Radio. (Click on image for larger view.)
Jacobus ZS1JDJ recently acquired a uBitx V3 HF Radio aka his "Red Ferrari". He used the radio a few times and wanted to add the headphone socket in order to utilize headphones with the radio. He followed the guidelines obtained from an Internet site only to find out later that the Audio IC (TDA2822) let out the magic smoke. He ordered several new TDA2822M IC's, removed the wiring to the headphone socket and inserted a new audio IC only to find that it also went up in smoke.
He contacted the author for assistance on how to fix the issue. The author was willing to assist but he had to do all the soldering and de-soldering himself under supervision of the author. This is how an Elmer share his knowledge after many years of constructing and fixing equipment. Unfortunately due to bad eyesight the Elmer is not working on radios anymore.
Jacobus ZS1JDJ visited the author and the "Red Ferrari" was opened on the workbench to see why the IC let out the magic smoke. I told Jacobus to de-solder the IC and provided a IC socket to make it easier to remove the TDA2822M in future. We gathered all the information on how to solve the issue from the Internet and also from the uBitx website.
There seem to have been a problem with certain IC's that does not "enjoy" 12 - 15 volt DC (Pin 2 VCC.)
Herewith a short explanation of the problem:
uBitx v3 Radio audio IC damaged after trying to connect phones
Damaging the audio IC (TDA2822M) on a uBitx v3 when connecting headphones is a known issue caused by shorting the audio output to ground during jack insertion. The TDA2822 chip in the v3 is highly sensitive to this, particularly if using a mono plug in a stereo jack, which shorts the ring to the sleeve.
Here is a guide to diagnosing and repairing this issue based on common uBitx community solutions.
Symptoms of a Blown TDA2822M:
No audio from the speaker.
The TDA2822 chip gets extremely hot when the radio is powered on.
Sidetone still works (if the issue is isolated to the receiver audio path).
A faint, distorted signal or a loud hum.
Repairing the Audio IC:
Remove the damaged IC. The easiest method is to carefully cut the legs of the 8-pin TDA2822 chip, then use pliers to remove the remaining pins one-by-one while heating with a soldering iron.
Install a Socket: It is highly recommended to solder an 8-pin DIL (Dual In-Line) socket onto the board rather than soldering the new chip directly. This makes future replacements much easier.
Replace with a Robust Component: Replace the TDA2822 with a new one. Some builders have found that specific brands (like "WX" branded chips) are more prone to failure, so sourcing a high-quality replacement is advisable.
Preventative Measures (Essential Mods):
To prevent this from happening again, you should implement one of these modifications:
Add Series Resistors: Add a 4-ohm to 8-ohm, 1/2-watt resistor in series between the uBitx output and the headphone jack TIP.
Rewire the Jack: Wire the headphone jack as a mono jack (using only the tip and sleeve) to prevent the shorting that occurs when a stereo plug is inserted.
Voltage Regulation: The TDA2822 on the v3 runs close to its maximum voltage. Providing a 6v-9v regulator for the audio stage can prevent future failures.
Troubleshooting:
If the replacement does not fix the issue, ensure the capacitor C77 (470µF) was not also damaged by the surge, and verify that the 12V supply is not exceeding 15V, as the TDA2822 is fragile near its voltage maximum.
Wiring up the headphone jack
It is recommended that when you wire up the headphone jack, you do not wire it up as a stereo jack. Inserting a mono plug into a jack wired for stereo (i.e. when connections are made to both the tip and to the ring connectors) will likely result in a short from the ring to shield when the plug is inserted. Several constructors have blown up their TDA2822M audio output IC as a result of exactly this scenario.
If you do want to wire the supplied headphone jack as a stereo jack, add a series 8 ohm 1/2 watt resistor (or perhaps a 4 ohm resistor) between the uBitx board and your phone jack. This should safely prevent any damage, though it will reduce the maximum available audio slightly through the headphone jack.
Reference:
Wiring up the audio connector so that you can also use an internal speaker
The headphone jack can be wired to connect normally to an internal speaker, until a plug is inserted in the jack, whereupon the audio is routed to the headphones. Again, it is recommended that the jack be wired up for a single channel (using the tip only) to avoid problems when inserting a mono plug into the stereo connector.
The jack’s tip has two connections (one is switched off when you insert a plug). Because the sidewall on the jack is “see through” you should be able to see how this works in practice when you insert a 3.5mm plug into the jack. Wire the terminal that is switched off when a plug is inserted into the headphone jack, to the positive terminal of your speaker. If your speaker’s polarity is not marked, it won’t matter which terminal on the speaker is connected to the jack.
The negative terminal of your speaker should be soldered to the shield connection on the headphone jack. To be clear, the wire from the main board and the wire from the negative terminal of your speaker are both soldered onto the rear (shield) tab of the stereo jack.
More information from the uBitx Web-Site about the issue:
TDA2822 problems - Reasons for failure CLICK HERE.
Now how did we solve the problem of the "Red Ferrari"?
1. Removed the blown IC
2. Fitted a IC Socket
3. Removed the 470µF capacitor (C77) and replaced it with a 100uF capacitor
4. Lifted the leg of pin 2 of the new IC which will be used to feed 7.5v DC to the IC
5. Installed a LM2596 DC-DC down converter module which was set to 7.5v DC
6. Connected the +7.5 v to pin 2 of the IC TDA2822M and pin 4 ground to the ground connection.
See images below for the above modifications
Jacobus fired up the "Red Ferrari" and tested it thoroughly. Problem solved!
Comment from the author (Elmer):
I am sure that Jacobus ZS1JDJ learned a lot from this event. (magic smoke release) Whenever anybody want to make a modification to a radio you must ensure that you know exactly how to do it. Google is your friend. Read as much about the issue as possible. The cons and the pro's. Do not be in a hurry. If not sure consult an Elmer before the smoke release. Any modification being done needs the correct equipment. If you do not have the correct "tools" or test equipment forget about the modification or let an experienced homebrewer assist you. Always have spare components available before you start. As stated before due to bad eyesight the Elmer is not working on radios anymore.
Images: (Click on images for larger view.)
