Boombox FIXED

[Superduper]

I am proposing a perpetual BOOMBOX fixes thread. This thread can be added to at any time whenever a member properly diagnoses or fixes an issue. Since some boomboxes have idiosyncrasies that is common to that model, other members can find these fixes invaluable. A perpetual thread might make it easier to find solutions to common problems. To facilitate easier search results and meaningful posts, the following (below) standard template is suggested. If making corrections, amendments, or addendums to or about your previous fix, please QUOTE your previous fix so we don't have to search through the entire thread to find all instances of the same FIX.

MANUFACTURER:
MODEL:
TYPE OF ISSUE: (i.e. TUNER, PRE-AMP, POWER AMP, TAPE, BELTS, etc)
SYMPTOMS:
FIX:
COMMENTS:
IMAGES:


====================================

I guess I'll go first:

MANUFACTURER: National-Panasonic
MODEL: RS-4360dft // RX-7700
TYPE OF ISSUE: Tuner
SYMPTOMS: No FM, Intermittent FM, crackly -- scratchy tuner dial, oscillation when volume cranked up.
FIX: Replace RF amp in FM front end with new 2SK49 FET to repair No // intermittent FM. Recap tuner board to fix scratchy tuner dial and oscillating FM
COMMENTS: The RF amp repaired the dead or intemittent FM. The tuner initially had a scratchy noise -- like an oxidized volume control. Since varicaps of this design are really air gap caps, oxidation should not be an issue. I have seen dust in the vanes cause issues before in other tuners so the vanes were blown out with compressed air. No improvement. However, another symptom worth noting is that FM began to oscillate when the volume was cranked. At first I thought this was an amp issue but since that symptom did not manifest in AM (or other mode), I immediately suspected the capacitors. The entire tuner board was recapped and when completed, I noticed improved separation, selectibility and the oscillation issue was resolved. There was far more detail to the music that was missing before. I am confident that this tuner is now fixed.
Comment #2: Healing Powers of Capacitor replacement. The difference in sound quality and performance between the before/after tuner work was very noticeable. I believe the entire boombox could benefit from a recapping as well. A note worth mentioning is that I tested every cap after the service and none of the capacitors suffered a catastrophic failure and tested within tolerance. However, the collective result of refreshing the caps obviously was very positive. The LCR meter I used is a very good one that is well regarded. However, there are some aspects of a capacitors operating characteristics that isn't as easy to determine if it should be replaced or not. Before the replacement, the tuner didn't sound well. It wasn't that it didn't work and I wouldn't say it sounded bad. But it sounded "old." Now, it sounds fresh, new. But there was nothing that suggested -- replace caps // fix boombox. A scratchy tuner dial is something we all could learn to live with. But I got to say that it's a refreshing change to listen to it like it is now. All I can say is, you don't know what you are missing unless you did a before/after. Rarely does a capacitor fail catastrophically. Normally, it's a gradual degradation of it's characteristics.

THE RF AMP (2SK49) IS SHOWN IN CIRCLE.

 

[redbenjoe]

for those members that have the guts to get so involved in the guts

this is a fantastic thread

 

[monchito]

norm i do like the metal tuner instead of the plastic box ,, those older tuners can really outlast just about any of the newer stuff

 

[Superduper]

Ramon -- I KNOW you have some fixes you can post, right?

 

[monchito]

i have to start doing that norm ,, i just enjoy reading your stuff to be honest ,,

 

[Marty Machine]

Great Topic, and should go well for logging popular issues.....

I love the old stuff, at least you can GET TO IT to test/measure things, let alone repair it !
I'm sick of opening microscopic surface mount toys of today....yuk! gimme an 80's boomer anyday

MM.

 

[blu_fuz]

Dude Norm! Write up one for that pesky sylinoid in the SK-550 cassette deck that jambs the head up and kills the deck

 

[blah blah]

we could call it the "superduper fixes" thread

i might make one here and there

 

[saxonman]

YES YES YES

 

[tec9]

MANUFACTURER: Promax / Tecsonic
MODEL: J-1 Super Jumbo
TYPE OF ISSUE: Would not power up with batteries
SYMPTOMS: Works fine on AC. does not power up with DC (batteries)
FIX: I first purchased 10 new D Batteries for this unit, and it would not power up. I checked and cleaned the battery compartment, and still had no luck. I opened up the box, and separated the front and back halves. by removing the many screws that hold it together. (you need a long screwdriver to get to them) I then had to remove three connectors (main power, clock power, and antenna leads) The back half has the battery compartment,and the power supply.Using a meter I was able to read the 15VDC from the battery compartment to the power supply. I unscrewed the power supply from a internal brakcket, and then removed the power supply. Once I removed the power supply I was able to take a good look at it. I was able to follow the voltage through the power supply and then stopped near the AC receptacle. It seems that this powersupply has a "automatic" AC/DC power switch- located inside the AC receptacle. Basically the connector that you would plug the AC cord into has a small switch inside it. When the AC cord is plugged in, it pushes the switch, and disconnects DC power. My switch was damaged, probably from someone jamming the power cord in and out too many times over the years. I desoldered the switch and added a jumper across it. This allows the DC voltage to pass at all times, so this is just a temporary fix, till I can source a new switch. It works fine this way, but you must NOT use AC power if you have the batteries in it. I have a feeling it would damage the power supply. So if you have Super Jumbo that does not run on batteries, but works fine with AC, check this switch.
DISCLAIMER- I do not recommend that you jumper the switch in your box- you run the risk of damaging the power supply if you provide AC power while a DC power is present. (plugging it in while batteries are in it)


COMMENTS:
IMAGES:

 

[Superduper]

Thanks for the post, machine gun man.

 

[oldskool69]

Great post!

 

[Superduper]

UPDATE FROM EARLIER POST- NOW INCLUDES A MOD FOR A BETTER FIX


MANUFACTURER: Promax / Tecsonic
MODEL: J-1 Super Jumbo
TYPE OF ISSUE: Would not power up with batteries
SYMPTOMS: Works fine on AC. does not power up with DC (batteries)
FIX: ..............I then soldered in a 1N5404 diode across the solder pads, which originally had the switch soldered to it. The diode blocks the any DC power from backfeeding back into the battery compartment, when you are running the box of AC. This allows the DC voltage to pass at all times, and you can still have the box plugged in with batteries in it.. It seems to work fine this way. So if you have Super Jumbo that does not run on batteries, but works fine with AC, check this switch, and if you find you have a identical problem, you could try this mod.

Interesting fix. My only concerns are that
(1) the IN5404 diode is rated at only 3-amps
(2) the diode will introduce a .7volt voltage drop so the 15 volt battery operation will drop to 14.3 volts will a fresh set of batteries and
(3) The batteries will continue to supply power as a parallel power source even as the boombox is powered up on AC.

How about consider incorporating a relay that turns off the batteries via a NC connection. That way, when the boombox is plugged into an AC outlet, it switches off the internal batteries. As soon as you unplug the outlet, the relay switches back to a NC position for the batteries. The downside is that this will consume an extra 20 - 60 milliamps (depending on relay choice) when plugged in but that's a small penalty to pay and will barely register on AC power consumption. Just a thought.

 

[tec9]

Thanks for your reply and information. I originally had thought of relay, but then had remembered a a similar application that used a diode to block a voltage backfeed. I thought adding this diode would be a clever way to fix this, without having to mount a relay and wiring inside the box. BUT after reading your points, I have to agree and will go with a relay. I plan on popping the box open again tonight, and installing a relay. I deleted my previous post on this, as I don't won't to put bad advice on this forum. As a side note, I did not see any voltage loss with the diode installed, probably because the box was not under load, and the cap was holding a charge. Thanks for your input Superduper, I will change my repair.
-Mark

 

[Superduper]

Thanks for your reply and information. I originally had thought of relay, but then had remembered a a similar application that used a diode to block a voltage backfeed. I thought adding this diode would be a clever way to fix this, without having to mount a relay and wiring inside the box. BUT after reading your points, I have to agree and will go with a relay. I plan on popping the box open again tonight, and installing a relay. I deleted my previous post on this, as I don't won't to put bad advice on this forum. As a side note, I did not see any voltage loss with the diode installed, probably because the box was not under load, and the cap was holding a charge. Thanks for your input Superduper, I will change my repair.
-Mark

Hey Mark -- you've obviously given this some thought so I believe you know what you're doing. The .7v forward voltage drop figure is derived from the spec sheet and consistent with almost all silicon diodes/transistors. Obviously, the relay is a way to allow the power supply section to work like originally designed by completely switching the batteries in/out of circuit. Installing a relay is a little more complicated and will either require a 120vac relay or a mini transformer or solid state voltage regulator to work. Please post your results when you finish the retrofit, which if working properly -- I would certainly consider a "fix".

 

[tec9]

MANUFACTURER: Promax/ Tecsonic
MODEL: J-1 Super Jumbo
TYPE OF ISSUE: Power -Will not power up on DC power (batteries)
SYMPTOMS: Works fine with the AC cord plugged in, does not work at all with batteries
FIX: Modified the existing power supply with a relay function
COMMENTS: Read Below
IMAGES

Okay- I've been battling this issue for awhile and came up with some proposed fixes, but I believe I have the last update to this problem. I'll start fresh with this post, so you don't need to read several posts and try and piece this together from them.

I recently acquire a Tecsonic Super Jumbo that worked fine when plugged in, but would not operate on batteries. I double checked the batteries, and the battery terminals- both checked out ok. I then decided to open up the box. After some troubleshooting I figured out the problem is a small switch located in the receptacle of the AC power input. (where you put the cord) This switch is located inside the receptacle, and when the cord is inserted it would depress this switch. The switch was damaged, probably from someone yanking the cord in and out it too many times! I tried to locate another AC receptacle and came up empty handed. I played around with solutions on how to fix this, and adding a relay to simulate this switch was the best solution. So here is info on the modification I did to allow my box to operate on batteries, with the broken AC switch. You need to have a 120VAC relay, some wire crimp terminals, soldering iron and some basic hand tools.

You need to open up the box, and the easiest way to open this box, is to keep it in it's normal upright position, and remove the many screws that are located on the backside of the box. Once all the screws are removed, you will be able to separate the back half from the front half-

Please note that you will have to remove three cables that are connected to the backside of the box.
1-Clock power connector
2-Main power connector
3-Antenna lead

Once you have disconnected the cables, the backhalf can be completely removed. This is the half that holds the power supply, transformer, battery compartments, as well as the DC and AC inputs.

We will be working with the power supply PCB , which should look something similar to this- (my main cap has been replaced)

You need to remove the power supply from the box. It is attached by 2 screws on the AC input, 2 screws on voltage selector switch, and one screw that holds the power supply to a bracket. You may also want to unscrew the large transformer, as it has several wires soldered directly to the power supply.
I desoldered the AC receptacle and removed the broken switch. I then flipped over the PCB and soldered two wires leads where the switch originally was. These leads are going to be going to a relay, the NC, and the Com connectors. The relay will simulate the switch that was originally there.
(Yellow wires attached where switch was originally soldered in)

I then soldered two more wires on the power supply directly on the pads of the AC input receptacle. These will be powering the coil on the relay
(Black and White wires will power the 120VAC relay)

I then left the 4 wires dangling on the power supply, and the screwed the power supply back in place. Once the power supply was mounted, I then connected the wires to the appropriate terminals on the relay. The yellow wires go the N.C. and common terminal, and the black and white wires go the coil power on the relay. I then mounted the relay in a acceptable location. The Super Jumbo is big, so you have a good amount of room to mount the relay. I mounted mine near the power supply, with heavy duty double sided tape.

Once the relay and the connections are secure, you can then put the box back together. The relay now works as the original switch did. As soon as AC power is applied to the box the relay gets power and cuts the off any power coming from the battery compartment. Once the AC power is disconnected the relay loses power and allows the battery compartment to power the box. Hope this helps someone in the future!
-Mark

PS- Thanks to SuperDuper for mentioning this to me. My last proposed fix had several questionable effects, this solution is the way to go.

 

[mellymelsr]

Excellent work!!

 

[docs]

MANUFACTURER: Toshiba
MODEL: RT-S932 (wireless remote control)
TYPE OF ISSUE: Tape Deck functions
SYMPTOMS: Deck will not always FF/REW or Play
FIX: A thorough cleaning (simple I know)
COMMENTS: This deck is not like others and has a motor that engages a cog which moves about 2mm onto each idler wheel.
IMAGES

Here is a picture of the deck.

You can see in the picture below that the centre cog between the two idlers has a tiny movement to make it engage one of the two idlers. Here there is a little bit of grease around the cogs which is ok but I think part of the issue was some grease and dirt inside the bracket which actually hindered the movement.

This is the same picture but with some clues as to what is what.

After removing the two screws to free the motor beneath you can then get at the plastic piece where the cog attaches to with three small movable clips. Pushing the clips inwards releases the cog from the front of the deck.

The cog and the hole in the deck where it goes were given a thorough cleaning with a degreaser and put back together. This made the deck function a whole lot better and touch wood has not had the same issue yet.

 

[Superduper]

Great post Docs. Overgreasing of cassette mech parts is soo common that it really needed to be pointed out. Many cassette mechanisms require precision adjusted movements and that center cog operates on the thrust of the motor to flip it against the proper gear, depending upon rotation. Many toshiba's use that exact same setup. Grease prevents excessive wear in high pressure locations but do hinder free movement. When lubricating cassette mechanisms, do not apply grease indiscriminately and only apply lubrication where prescribed by the manual. Also, remove old grease before applying new.