DJ Tech strange issue.....

[Superduper]

Your inch measurement isn't useful because it goes by decimal, not fractional. For example: .12" x .06" = 1206 package size. As you can see, your ruler isn't going to get us the imperial answer. But based on what it appears as far as I can make out, on your MM scale, it is likely 3.2mm x 1.6mm right? This equates to 3216 which is the same as 1206. You can verify, best to use a digital caliper. Remember, don't add the solder blob -- that part isn't included in the size.

That's smaller than I thought, get the largest power rating you can find in that size.

You can get from Mouser or Digikey which are trusted sources and they are cheap, but for 2 resistors, you are going to pay $8-$10 shipping which is their minimum charge. You can get from eBay shipped to save on the shipping but if you do, best to get name brand ones instead of unbranded ones and choose a USA seller otherwise you are going to wait a month, sometimes 2.

If you are unable to get the old ones off, and you need help and can ship the board safely, I can do it for you, just fyi, but unfortunately, shipping charges these days are through the roof.

 

[blu_fuz]

Yeah probably 3.2 x 1.6mm

Keeping to the 1% rule, mouser has a nice selection but I don't recognize any of the brands.... I was going to pick the Panasonic but those are 5% tolerance.

TE Connectivity
Yageo
Vishay
Neohm
Dale
KOA Speer
IRC / TT
Holsworthy

 

[Superduper]

I have used Yageo, Vishay, KOA Speer, have had no issues. Panasonic is probably fine, get a few & use 2 that are closest in value.

 

[blu_fuz]

I went with the 5% Yageo.

 

[Transistorized]

Wow! I am curious to know if something went wrong in this circuit or if all DJ-Techs are going to do this with normal operation?

I say this because your wife's DJ-Tech resistors look fine. I wonder if these resistors could be tied to the USB power port on the front? It has a limit to the charge amperage it can handle which is 200mA at +5V. I wonder if this could be the result if a device such as a phone is connected to the USB and doesn't throttle its charge rate to 200mA. I have only attempted to plug in a USB stick and have never used the DJ-Tech USB to both play and charge my phone. Some phones you can turn off the charge feature on a USB connection and only allow data transfer upon connection. Without seeing how these are tied into the circuit for power transfer I can only assume the powered USB could be a possible cause for overheating them

If so, I am wondering if there is any way of radiating heat off of the factory resistors without shorting them.

 

[Superduper]

No service manual, who knows what those resistors is for? I think Joe also used a larger non-standard sized battery too didn't he?

 

[blu_fuz]

Yes on both points. This radio has the upgraded battery and my wifes does not. Hers stays plugged in all the time in the kitchen. Mine on the other hand is plugged into the camper most of the time. I did notice that mid summer 2019 I tried to use the USB port just to charge and the radio had a **** fit, like it couldn't connect to BT and have the ipod charge via USB at the same time and it would randomly kick the BT signal on and off. I unplugged it and didn't try to charge or connect direct to my ipod through the USB ever again.

 

[caution]

I suppose it's possible that a larger capacity battery can stress the stock charger, takes more time to charge up.

I'm thinking they're regulating resistors for the charger. I had to replace an undersized resistor on a cordless drill charger, probably because the battery died and wouldn't hold a charge anymore. If the voltage coming back from the battery is super low the charger will think it needs to send lots of juice, but on a normal battery this wouldn't happen, even one that's drained but still chargeable, it might get hot for a bit, but not enough to fry it because after not that long, the battery's voltage approaches source voltage and less power is delivered.

 

[blu_fuz]

I have tried to charge this radio with a 'dead as a doornail' battery multiple times. Usually the charger won't kick on properly when the battery is that low so I have to remove the back, disconnect the battery from the boombox and put a 12v charger on the battery.

 

[blu_fuz]

Resistors are here. Hopefully tonight I can get them swapped out and be jam'n.

 

[Transistorized]

I am rooting for ya man

 

[blu_fuz]

I need help

There is no pad on the circuit board to solder to.....




There is too much glue on the plugs, can’t even remove the board. Bull ****.

I’m just going to blob some solder across the areas I marked in red because there just isn’t any pad left on the pcb.




I cut tiny parts of the legs off this LED to make jumpers.....

Testing now.



It’s working for now like it should but I think I should have bridged both sides of the new resistors..... i dunno.

 

[Superduper]

What's all that residue that's blobbed there which wasn't there before? Didn't you clean the area thoroughly first? Also how did you remove the old resistor? It's hard to do unless you heat both sides of it at the exact same time. It's too late now but the easiest is with hot tweezers, 2 soldering irons simultaneously or using hot air. As for the solder blob connections..... if the originals wouldn't last with the connections they had, these may fare worse.

Frankly, I think you may be better off confirming where each pad is connected to. Then stretch a single standard 1/2w, 3/4 or 1w resistor across those solder pads. If no solder pad, then you'll have to expose some copper from the solder-resist and create a new solder pad. A 16.5Ω resistor will be a perfect match to the pair but something close will probably be fine. I think I see a standard through-hole solder pad that stretches about an inch from the right side of those resistors in the above photo. The left is a bit unclear until you clean that area up a bit.

Now, you probably don't want to hear this but you may want to reconsider using oversized batteries. The circuit isn't designed for it. Larger batteries will last longer but when exhausted, will become hungrier during charge. I'm not certain that's what is causing those resistors to fail but the next time they toast up, that may be the last of that PCB. Might want to consider the risk vs benefits of keeping the oversize battery in there.

 

[blu_fuz]

The dark residue is something that pooled up when I removed the original resistors. I probably should have tried to wipe it off to make sure the pads were clean and ready for the new resistors.

If this ‘fix’ doesn’t hold then I will try the single resistor idea you have.

I believe you are right, the large battery, when the charge is low, really runs a lot of current for a long time probably frying those resistors.

I did a quick 2 hour charge and had a decent jam session in the garage for a couple hours and I have to say that my hack job repair is working. Maybe I will limit the charging time to hopefully avoid cooking it again.

 

[T-STER]

Yikes, i have put my smaller og battery back in now just in case!

 

[jimmyjimmy19702010]

You might consider bypassing the factory setup and just connect an external smart charger directly to the battery via a fuse. The charger will take care of the charge rate etc. That’s the setup I use on my 7.2aH SLA equipped DIY boxes with no issues to date.

 

[blu_fuz]

Part of me thinks that the oversize battery isn't the issue. The battery charges properly, it discharges properly, charger is working the way it should, LED indicators on charge level work properly. Literally, the only thing effected by the blown resistors is that the BT signal disconnects and clicks the box on and off over and over if you use it in BT mode. Radio mode and using any hardwired input, the radio works flawless on battery or with the charger plugged in.

Only have I seen this before is when I used my USB cable plugged into the radio to charge my ipod while it was in BT mode. The boombox doesn't like that one bit. It was killing the BT signal to try and read the files through the cord/usb and it would switch back and fourth by itself. That might be the real issue here why the resistors blew.

It could go either way but there is no indication that the battery or charger are faulty......

 

[Transistorized]

Yikes, i have put my smaller og battery back in now just in case!

I doubt the larger capacity battery did this damage. Its not more powerful just has more storage capacity. I suspect what causes this issue is pulling too much current through the USB port. Personally I would not use this port for anything other than a USB stick. While it can charge I wouldn't recommend it

 

[trippy1313]

Well this is quite interesting. I was using my DJ Tech pretty much every day since I got it from you Joe. But since work got shut down it's still there.

So is your BT still acting up after this fix? Sorry if you mention it, I'm tired. I thought I read it's clinking off?

 

[blu_fuz]

It is back to 100%.