M70 LED meter mod

[caution]

So I've been researching the idea of making the MMS lights above the cassette door on the M70 be dual-function, because how awesome would that be if they could be VU meters?!? I think it was Cpl-Chronic that correctly pointed out that trying to add a switching circuit to these would be too difficult. Well, I think he used the word impossible, but that only emboldened me!

Dual and triple (RGB) color LEDs exist, but they all share a common cathode. What I need is a pair that are isolated in the same package, but that doesn't seem to be available so I thought how about two separate LEDs? The surface-mount ones are so small (I've got a jar of 12,000, they're like sand!) that I could easily fit a pair side-by-side in each hole. I'd wire one set to the regular MMS circuit and the other set to a VU meter circuit, such as a pair of these LM3915 chips. There also seems to be enough space in front of the LED bracket to add a diffuser sheet if needed.

I'll probably end up using a line-level signal as the input, so they're bouncing independent of the volume setting. The C100F does this and is sort of annoying, they just max out at a certain point. The only disadvantage would be that a quiet tape or input signal would not do much on the meter.

If anyone knows about the M70 dial lamp LED upgrade kit, I'd be really curious to know how much power that chip can offer, because I'd like to hang the LM3915s off that so they can turn on and off with the dial light LEDs.

Speaking of which, I'm about to order the kit but I cannot decide on blue or white, what do you think would look better with red VUs? Heck, the VUs don't even have to be red, but I do like red

 

[k2j]

Hah, how funny. You just reminded me that I ordered a LED kit from super last summer. Guess its time I installed it. Oh yea and clean that damned function switch.

Nice idea by the way

 

[Superduper]

If the lamp upgrade kit you speak of is the one I sell, then the following technical information might be of interest to you.

The chip does not drive the LED's directly. The chip drives a NPN transistor 2N3904 (or BC337), which drives the LED's. I don't have the specs handy regarding that transistor but the datasheet is commonly available on the web. Just google that transistor and you can get full specs on it. It is powered via a 12V regulated rail.

However. It is also important to know that the LED controller/driver circuit in question (if wired according to my installation instructions) is likewise powered via the M70's X505 regulator (2SD439E). That regulator powers more than just the LED driver/controller circuit so regardless of what the power handling capability would be for the controller, it is always subject to the amount of available power taken from X505. The service manual does not specifically address either the total power handling of this driver or the amount of available power to the lamp circuit. It is presumed that the LED kit as designed does not deviate significantly from orig design with the incandescent lamp. This limitation described will not apply if the controller obtains power from a source other than X505 and if that is the case, then the limitation of the controller will be either that of the 2N3904 or the new power source, whichever is less.

Lastly, I designed the controller board with the ability to add a DIP (or SIP) relay on the board for future or custom use of the module for purposes beyond which I currently have it set up. That will effectively free the controller to power virtually anything subject to the power handling capability of the relay, which is a lot if the output is on a relay, or to change the circuit to a positive relay driven trigger (currently it is setup for a negative trigger). Some custom point to point wiring will need to be added depending upon the relay used, but I surmise that anyone interested in such custom application would not be deterred. Hope that answers your question.

 

[Lasonic TRC-920]

This idea could go beyond just the M70. Many radio's with the search feature has these LED set up's in place, Toshiba comes to mind.

Very interested in where this thread will go.

 

[caution]

I'm looking at the one on Analog Alley, is that yours? I do see a little empty DIP land pattern on there. I was actually thinking of just powering the circuit straight off 12V since the chips can run from 3V to 25V, but voltage regulators are cheap, I could add one if need be and leave X505 alone. I don't think it'll be an issue since the 3915's directly drive the LEDs.

Thanks so much for the reply!

 

[caution]

So my dial light LED kit arrived (thanks Norm!) and drew up a little schematic for it, and noodled over how to modify it to have a four-state loop for my modes:

00: All off
01: Dial lights on only
10: LED VU meters on only
11: Dial lights and LED VU meters on at the same time

As luck would have it I have a 2-bit counter if I simply tie the output of the flip-flip now in use to the input of the second one in the 4013 chip, then connect the second flip-flip's output to a second 2N3904 (or something beefier) that switches the low side for a pair of LM3915s and their VU LEDs. Not sure on which polarity output or how data/set/reset should be tied in order for it to come up in "00" mode but shouldn't be a huge chore to tweak it once I get things wired up on the bench.

I purchased a pair of tiny LM3915 kit boards that have just enough room for all the essentials, including spots to solder the wires going to the tiny SMT LEDs I'll be using. I also decided to use a 7809 9V voltage regulator to power everything instead of X505, since 15V is a good input voltage and 9V is an acceptable level for the 3915s and the 4013.

 

[JustCruisin]

 

[blu_fuz]

I cant wait to see how this comes out.

 

[Superduper]

If I might make a suggestion here, while converting my controller to accommodate a second device (LM3915's) can be done, why not just do them as separate retrofits instead of having the light switch toggle everything. The reasons I say this is:

1. You would have to cycle through 4 clicks to turn off the lamps instead of the normal on/off.
2. The 2nd set of flip flops, since unused, are grounded. Either the traces would have to be cut, and it's a 2-sided board, or the pins would have to be severed to unground them.
3. Changing the source from X505 to your own added regulator is fine but if you do, you should remove the resistor that powers the meter leds and install a jumper instead because the circuit is currently setup for 12V and the other resistor for the dial leds should be changed to a value matching the brightness you desire with the lower volt setup.
4. Changing the source from X505 to your own regulator also introduces another change... regards wiring. Currently, once my setup is installed, NO additional wires are tethered from front cabinet 1/2 to the chassis. My original kit did have separate wire connectors and this was a pain in the butt if you frequently assemble and disassemble to line everything up without pinching the extra wire. Maybe this isn't important to you but you should be aware that this will be the case. IF you do your vu meter mod separately and not tie to this one, then since the VU meter assembly is part of the chassis and not the front case, any wiring can be localized there and not added to the front cases.
5. The VU meter mod is cool. But not sure why you would want to turn it off. How about just wire it so it is on with the amp unrelated to dial lamps?

Anyhow, just some food for thought.

 

[caution]

Excellent point. Yeah, usability takes a hit trying to preserve stock status, not to mention the three clicks every time on power-up, since I'll always want to see the VUs. The switch would probably start to wear out (and the paint around it) from so much use. That would annoy me more than seeing the MMS lights on at the same time as the LED VUs, since I never use MMS.

Luckily the traces are all accessible, but I won't be modding it in light of your first suggestion. The LED VUs are probably enough of a show for me, but it's nice that there's the option to add clicks to do, say, more dial light-related stuff (colors, pulsating to music, etc.), and even then it wouldn't be too hard to add a 9V wire with a breakaway.

 

[Cpl-Chronic]

I still think you will get into trouble once you start modifying the LED circuits for the new hardware. You really can't mix electronics that way without affecting the original circuit in an in-calculable way. The only real way to make those leds into a VU is to separate them completely from the music search circuit & dedicate them to your circuit only which means you have to literally remove each LED from the original circuit & re-wire them, with resistors, to Norm's controller which is in effect only a latching IC design. Too simple for a proper VU meter type of circuit.

I'm waiting to see the outcome. Hopefully, you have these issues in mind before you destroy a perfectly good working music search system.

Good luck,
Cpl

 

[caution]

Nahh I'll be fine. The only thing I'll be doing to the MMS LEDs is switching them to smaller SMT versions that can live next to a second SMT LED at each location. The second set of LEDs will only be wired to the LM3915s. The most challenging part will be modifying the LED bracket and lining up all of the LEDs. I'll have to glue each one on a tiny strip of material and carefully solder each one. I even purchased a new soldering station with smaller tips to do this.

Believe me, I'm doing all my homework up front before I start doing any mods. This thread has been enormously helpful.

 

[Cpl-Chronic]

Ahhh... I see now what you want to do. Should be an interesting project...

Cpl

 

[caution]

I finally got the LED VU meter kits, so I spent yesterday assembling those and getting everything disassembled, cleaned and prepped. After thinking about it I decided that instead of replacing the currently existing LEDs with a pair of different ones, I want to keep the original set and use them for the VU meters. As you may know, they have custom molded lenses on their tips and really fill in the space in a way that looks nice, and I'd hate to lose that from some super-bright point of light that doesn't fill the spot well. So, where to put the other LEDs for MMS. Well, even after trying to shove it up under the main LED between its legs (giggity) it would not shine enough light around the leadframe of the main LED. I thought about drilling holes into the side of one of the brackets and just have the light shine through that, but I didn't want to risk ruining the brackets. I've decided to sneak an LED into the space between the brackets created by the extra material under the arrow holes on the ends. I had to dremel out a portion of this lip on each one in order to get an LED shining onto the arrow LEDs, so I did one of those first as a proof of concept. The idea is that the MMS lights take a back seat to the VU meters, and will not be terribly obvious when in use, so they don't detract from the meters. I used green since it's already the color of the one LED I won't have to add a second one for, and it contrasts well with red since it's a combination of the two other primary colors. I glued down a couple last night with some E6000 and it worked well, except that the wires work better if they both come out the same side, and if the LEDs shine sideways.

 

[blu_fuz]

Im watching this!

 

[caution]

Well, the tiny LEDs, as bright as they are, don't cut the mustard. After some more noodling I discovered that if I bend up the legs on the original LEDs, the distance to the PCB is exactly the same as the height of the 16 yellow LEDs in the two VU meter kits. You can see in the pic how their bottoms are flush with the white bracket. I did have to grind down two of them to fit under the arrow LEDs on the ends, where there is less clearance. Since I had the room, I tried centering two LEDs at each location, and then just a single one. The single setup was actually brighter, whch is a very, very good thing because this means that they line up with the holes in the board, so the entire thing can just drop back down, but I still need to decide how to resolder them since the pads are on the same side. I'll worry about it after the glue dries.

 

[caution]

Dropped it in this morning and wired up the MMS LEDs. There's a nice little pocket above the MMS IC for the two meter boards. Did a power-on test and everything seems to be working as expected...

https://www.youtube.com/watch?v=A01iJVUk5Eo

 

[blu_fuz]

Cool cool, now get the vid of the LEDs working as a VU meter!

 

[hemiguy2006]

Very nice work!
Impressive to say the least!

 

[Lasonic TRC-920]

WOW dude, this is seriously kicking ass!