Strange malfunctioning LED audio peak level meter problem

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

Hello.

Did this work in the end? I have an Harman Kardon TD292 with LED VU issues

No. I gave up and moved onto other projects. Bad led meters are a common problem with this model. Bad design. They should've used regular SMD leds.

[edom31]

Re: Strange malfunctioning LED audio peak level meter problem

Hello.

Did this work in the end? I have an Harman Kardon TD292 with LED VU issues

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

So I used solder wick to remove everything I did to the LED VU board and plugged it in. The deck played fine and no blown fusible resistor! Yay!
I plan on trying this one more time. I'm going to go about it the way I had originally intended, which is to wire the led leads to each other first and then connect them to the board with as few connection points as possible.

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

Be careful as any shorts on the LEDs/wiring is stressful to the COB chip on the module.

Yea. I hope I didn't damage it. There's an 8 pin connector on the led module. I wish there was a way to use that to check for shorts. I went across all of them with a multimeter, but none of them gave a continuity tone.

[redwire]

Re: Strange malfunctioning LED audio peak level meter problem

Be careful as any shorts on the LEDs/wiring is stressful to the COB chip on the module.

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

it does not work like that, leds draw as much power as you give them.
the rest of the circuit decides how much current they get.

So I replaced the fusible 4.7ohm 1/4 watt resistor and unplugged the led display module. It has been running about 15 minutes with no issues, so I'm assuming it was the led module that was shorted or drawing too much current and I didn't fry any other parts beside that sacrificial resistor.

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

I've ordered some 4.7ohm 1/4 watt fusible resistors (FRM-25JT-52-4R7). I'll replace the resistor and leave the led board disconnected to verify no other damage occurred and the machine is working (minus the led display) before proceeding.
I'm actually kicking myself for not following my plan. You can wire 3 LED's in series and connect only the two remaining ends, but for some reason I started wiring each led in independently, which resulted in way more work and every solder joint increases the odds of something going wrong.
I've pulled all the resistors off the board and I'll go over it with some solder wick to get a good second start at this. Anyone that has looked at the led board schematic have any good advice on how to check if there's a short? Thanks!!

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

it does not work like that, leds draw as much power as you give them.
the rest of the circuit decides how much current they get.

Ah. Ok. So I guess I shorted something on the led board then. I'll take a close look at it. Thanks.

[stj]

Re: Strange malfunctioning LED audio peak level meter problem

it does not work like that, leds draw as much power as you give them.
the rest of the circuit decides how much current they get.

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

Update... ok. So I messed up. I ordered the below listed LED's and began installing them in 3's, since that's how they're connected in series, after which I would test them by playing a cassette. The first set of three worked fine. I installed next set of three. Those worked great. I installed the next set of three. They worked great...for a few seconds. Then I saw a puff of smoke. It was the fusible resistor on the power supply. I assume the LED's were drawing too much current. Ugg.

EDGELEC 20pcs Prewired 0805 Green SMD LED Light Emitting Diode DC 3V Micro Litz Length 7.8in. (20cm) Soldered Mini LED Lights for DIY Manual Model Toy Decoration https://www.amazon.com/dp/B07FN5HVPR..._4wvtFbTHYBD2Q

[redwire]

Re: Strange malfunctioning LED audio peak level meter problem

I quickly found one here, other stores are lower price https://www.aliexpress.com/item/4000143963406.html
youtube video on it https://www.youtube.com/watch?v=KL5S2Z7fnM0

The LED bars' part number "aktech 190802" but no datasheets on it.
"PCB the size of 80*14mm, LED module area : 58*14mm"
https://www.aliexpress.com/item/32848296152.html

The original board seems to have four wires: L, R line level, GND, +10VDC power.
The new board would just wire in direct (it has two ground wires) but I'm not sure how to calibrate it; it must be done in software.

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

After a good cry, I would do the surgery on the old pc board. Get a bunch of 0805 or 0603 LED's (old style yellow green) and scrape off the old ones and some solder mask with an exacto knife. Then some flux and solder on the new LEDs.

There are 12 LED VU meter displays and/or kits that might fit as well, from fleabay or Ali.

I would do the same if I had the tools and skills. These parts are way way smaller than anything I've ever worked on before.
That led meter looks nice. How would you wire that to the board? I imagine you'd have to tap into the audio signal going to the old display's circuitry, cut it and reroute to this display? I looked at the one you suggested. I'm surprised they don't give better specs on its size. The face of the cassette player has holes that these LED's would have to line up with.

[redwire]

Re: Strange malfunctioning LED audio peak level meter problem

After a good cry, I would do the surgery on the old pc board. Get a bunch of 0805 or 0603 LED's (old style yellow green) and scrape off the old ones and some solder mask with an exacto knife. Then some flux and solder on the new LEDs.

There are 12 LED VU meter displays and/or kits that might fit as well, from fleabay or Ali.

edit: the description is too funny:
Display effect:
1. strip show after peak travel whereabouts
2. strip show after the disappearance of the peak travel
3. The strip display (no peak display)
4. strip show right after the peak flow disappears
5. The strip display (three lights)
6. striped marquee display peak effect
7. Peak strip show right jump lamp lights two bits whereabouts

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

each led takes about 2v so with 3 in series that WORK - each will show the same voltage.
the microscope is not supposed to be that close to the board btw!

Unfortunately that microscope has to be "on" whatever you are looking at when it's set to max magnification.

[stj]

Re: Strange malfunctioning LED audio peak level meter problem

each led takes about 2v so with 3 in series that WORK - each will show the same voltage.
the microscope is not supposed to be that close to the board btw!

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

https://www.aliexpress.com/item/32423249665.html
those are great - 5 colours - 20 of each for about $3

So I've killed most of the LED's by now. Those exposed microscopic wires are ridiculous. Trying to use that crappy usb microscope I was dragging it all across that board. Only a couple of the LED's still work. So I measured one at around 1.5v and the next one beside it in the "3 led group" was measured at 3v. I couldn't get a voltage reading on the third one in that "group". Do u think it would have been 1.5v higher or double the one before it?

[stj]

Re: Strange malfunctioning LED audio peak level meter problem

https://www.aliexpress.com/item/32423249665.html
those are great - 5 colours - 20 of each for about $3

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

https://www.amazon.com/EDGELEC-Prewi.../dp/B07FN5HVPR

Would these work?

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

You can test each LED as suggested, and also use high power magnifying glass each bonding wire of the LED.
I also see strange trace layouts.
I am also surprised that exposed bonding and die last this long, but since they cannot put black blob on top like they did for the IC since they are LED, they could have put on clear sealer instead on the LED's.

Unfortunately I have neither the tools nor skills to both view, manipulate, and solder those microscopic wires in place.
I CAN solder some jumper wires to some of those larger exposed traces and test points to some wired-led's.

Based on how these traces are laid out, I should only have to connect 9 jumper wires to the board. 1 of those 9 wires will break out into 8 wires itself, which will go to one side of the 1st, 4th, 7th, and 10th led's on both rows. The remaining 8 wires connected to the board will connect to the "other" side of the 3rd, 6th, 9th, and 12th led's on both rows. The remaining led wires would connect together depending on where they fall in the arrangement.

[JimBanville]

Re: Strange malfunctioning LED audio peak level meter problem

Plastic housing