Process: Repair, Modification, and Restoration
When a new boombox arrives it gets a complete evaluation. Each feature gets fully tested and an intake sheet is filled out that details any issues and logs other important data about the unit. We typically purchase broken boomboxes because they are cheaper and we enjoy rescuing these units from the brink of being tossed away forever. These boomboxes were made back in the days before electronics were regarded as disposable so they are certainly designed to be worked on. However, the spaces inside are tight, schematics are almost always non-existent, and replacement parts simply do not exist except for simple caps and resistors. It can take some creative engineering to get these units running again.
Tape Deck Repair:
Almost without exception the tape deck does not work and this is perhaps the most complex part of a boombox. Every seller assumes “oh it just needs a belt.” This is virtually never the case. And if it does “just need a belt” it’s because the old belt melted and turned to goo inside the unit. I have yet to find a unit with a perfectly broken belt lying inside the case and just had to pop a new one on. Tape decks can require alignment, cleaning, demagnetizing, speed tuning, and other complex mechanical adjustments all in addition to simple belt replacement. For speed adjustment I use a cassette tape that plays a 3000Hz audio tone and then sample the signal with a frequency counter and finely adjust the speed of the capstan motor.
Knobs, Switches, and Buttons:
Static pop is always an issue with old boomboxes. The potentiometers behind the knobs sometimes need replacement but always need cleaning. I’ve had to take switches apart, clean all the contacts, and then be very careful to place back every spring and clip where it belongs. The potentiometers can be replaced but a lot of times the switches just simply don’t exist anymore. Repair is necessary in these cases otherwise an entire other unit must be found in order to replace a single switch. Obviously, repair instead of replacement is the most cost-effective solution.
Each boombox is different and without schematics things can get tricky if there is an issue in this part of the circuit. However, these circuits were designed very well back in the 80’s and problems here are rare. Also, most of the main amplifier ICs can be found online still.
More well-designed circuitry here! Problems are rare but usually easy to solve. There are a number of adjustable parameters (FM/AM OSC tuning coils, sensitivity adjustments, the free-running frequency of the VCO, etc.) on these boards that need to be checked if there are issues with the radio. Printed resistors seem to be a consistent issue but can be removed from the circuit and replaced with discrete resistors without much headache. Bad electrolytic caps are also common but difficult to find.
I’ve had a few boomboxes that wouldn’t power up due to bad caps, a shorted diode, or bad power switch. These are fairly easy problems to find and fix.
Once all repairs have been made then the boombox circuitry can be modified to add Bluetooth. The process is different for each boombox since the circuitry is always different.
The first step is finding a suitable DC voltage inside the boombox. This is far more preferable than starting with the input AC voltage because then the bluetooth would not function when operating the boombox on batteries. These things are portable after all! Anything in the range of 6-18VDC is fine. This must be converted to an isolated 5V supply to power the Bluetooth. The key here is that it must be isolated from the rest of the boombox’s circuitry otherwise a ground loop is created with the amplifier circuitry and the associated noise will render the Bluetooth inaudible. I have created a custom PCB for this part of the circuit that gets installed into the boombox.
From here the Bluetooth module is added, a switch that shuts the power to the isolated supply off, a 3.5mm audio jack, and an led to indicate Bluetooth connection. Boomboxes usually contain an aux input but RCA jacks were used for this input connection. You could hook your phone or other portable audio device up to the boombox with these jacks but you would need an adapter. Providing the 3.5mm audio jack is not necessary in these cases but it is an added convenience that I'm sure will be appreciated. I drill three ¼” holes in the back of the unit in a discrete location not interfering with any labeling and install the switch, led, and 3.5mm audio jack. The components are all located inside the unit wherever they can fit without shorting anything (space is very limited and this often involves quite a bit of work!) and the boombox is closed back up and is ready for cleaning and detailing.
This part of the process can take longer than the repair and modification and a strong attention to detail is needed. These boomboxes have been around for over 30 years now and along the way they have been dropped, bumped, scraped, stained, and scratched. The chrome has often peeled in places and the metallic paint has been rubbed off in others.
First thing to do is to match the boomboxes color with a suitable metallic paint. We use Testers model paint that is available in a variety of metallic colors for the model airplane and rocket hobbyists. For the chrome we use a chrome pen that is good for touch-ups. We use cotton pads on Dremels and drills with buffing and scratch-remover compounds. We hand scrub all the little nooks and crannies, of which there are a million, and we remove and polish all the knobs, switches, and buttons. Sometimes the speaker grills need repainting due to rust, discoloration, paint splatter, or other stains. These are removed, spray painted, and then, while still wet, the holes are blown open again with an air compressor. It can take hours upon hours but the makeover can have miraculous results! Besides, if you go through all that work to make these boomboxes sound great again then it would be an injustice not to make them shine once more too!
The entire process from start to finish can take as long as 12 hours per boombox depending on the condition it starts in. In the end you have a beautifully restored boombox with the added modern functionality of Bluetooth. You just can’t get that classic look and sound from modern audio equipment!