FIXED! Sanyo Projector With Shorted Inductor & Transistor

[Fixin Stuff]

Hi peeps. I'm revisiting a botched repair from years ago from a Sanyo projector which I released excess smoke from (see pic).

After refurbishing the projector to remove all of the dust from the lenses, LCDs etc, during reassembly, I accidentally mixed up two of the plugs and connected them back to the wrong place on the board, and there was a fizzle and puff of magic smoke when I turned it back on    Unfortunately no genie appeare...

I tested the neighboring components (L5606 & L5607 etc) which looked identical to the frazzled component, and they had zero ohms resistance. Back then, I didn't know that 'L' meant inductor, so I assumed they were zero ohm resistors 

So I soldered an ugly solder blob across the section of the board, and it does actually work! But the fan runs at 'ludicrous speed' instead of what it ought to with the usual start-up sequence.

Now I want to see if replacing the ugly solder blob with the correct component will make it work properly again, or if other damage was done. But I did some research on the part from the service manual and searching online. I've posted the part number, circuit diagram, a photo of the component on the board etc all in the image. The actual component is L5701, but there's just the solder blob there now (my soldering iron's element died the other day too so I can't remove this right now). The components next to it (L5606 & L5607) are identical, and they have the same part number in the service manual. They also measure zero ohms resistance.

I can't tell if I should be looking for an inductor/ferrite bead etc, and what specs I would need in terms of current rating, voltage etc.

If anyone in the know could please take a look at the pic and let me know what component I need to replace L5701 I'd be very grateful!

[Fixin Stuff]

Here's an expanded view of the circuit diagram which the component is part of

[helius]

Ferrite bead. The inductance is not too critical, it mainly protects the circuit from picking up RF switching hash.
When an inductor is listed as "330 Ohm" instead of microhenry, it refers to its inductive reactance (X_L) at a particular frequency.
X_L = 2 pi f L
where L is the inductance. This is the impedance of the inductor to a sine wave at some specific frequency, probably around 10 MHz. If you use a multimeter that uses DC or a low AC test frequency, it will be around zero instead.

[Fixin Stuff]

Thanks for the response Helius.

Was also helpful to know the application of this in the circuit ("it mainly protects the circuit from picking up RF switching hash").

Based on your message, I've found these options which say they are good for EMI suppression, and which are about the right physical size. I know metric measurements like millimetres are like witchcraft to some Americans 

There are various options of impedance at different MHz of 25,100, 300,500 and 1000. Only the 100MHz option seemed to have a 330ohm range in this size and application (see pic).

I was just going to choose one with a high current rating, but then I saw there's quite a wide range of maximum DC resistance which doesn't necessarily correspond to this.

Any further selection help is very much appreciated.

[james_s]

If the ferrite bead burned up then other parts have likely been damaged, is the IC that controls power to the fan involved in that part of the circuit? You'll probably find that the fan control IC or external transistor if there is one is shorted resulting in the fan running full speed.

I hate it when equipment uses multiple identical plugs. When I encounter that I usually mark them with colored permanent markers.

[Fixin Stuff]

Hi James. I was hoping (probably stupidly) that the ferrite bead may have acted as a rudimentary fuse when it blew open-circuit. But as you say, more damage is possible/likely. Your hypothesis about something being shorted causing the fan to run at full speed makes perfect sense and you're probably right.

It also explains why the projector wouldn't start work at all when the fan circuit was open after the bead blew, but why it would start when the circuit was closed by my solder blob (even though the fan speed was un-controlled) as the fan circuit is part of the protection circuit.

Fortunately this projector has a very comprehensive service manual available for free here: https://elektrotanya.com/sanyo_plc-xw56_sm.pdf/download.html (After clicking to confirm you're not a robot, it actually took a good few seconds for the download to be ready).

It has the fan control circuit on page 44. There are quite a few ICs in the circuit, and I'd be very grateful for any advice on how to begin to troubleshoot this circuit. I've only got a basic DMM for testing. No scopes and fancy gear like the big boys    But the fan's speed will quickly show whether something has been resolved or not.

I hate it when equipment uses multiple identical plugs. When I encounter that I usually mark them with colored permanent markers.

Guess how I learned this lesson?!    I now take photos of everything BEFORE I take it apart too... 

[Fixin Stuff]

What the heck, here's the fan control diagram to save contributors time 

[james_s]

Where does that S15.5V come from? I don't see anything else that would control the speed of the fans. Then again Q7812 and the other similar switch are drawn as if they're relays but Q is normally a transistor, if those are indeed transistors then they may control the speed of the fans.

[Fixin Stuff]

Thanks for the help, James. Here's more of the circuit diagram showing the two ends of the 15.5V.

I've also attached a pic of the protection circuit which includes the fans.

Let me know if you need more info either side of this

[james_s]

Is Q3582 a mechanical relay as the drawing implies, or a transistor as the reference designation implies? Unfortunately that isn't a schematic, it's just a block diagram, there are a lot of missing details.

[Fixin Stuff]

Hi James. Sorry about that, here's a pic of Q3582 and a part number from the service manual.

Here's a link to a part with the same part number, which says it's a bi-polar transistor: https://www.chip1stop.com/USA/en/view/dispDetail/DispDetail?partId=TOSH-0089256

[james_s]

I would check both of those transistors, I suspect one or both of them are shorted, resulting in full voltage to the fan at all times. It should be trivial to test them with the diode check function on your multimeter. B-E and B-C junctions should both behave as diodes.

[Fixin Stuff]

That's really helpful, James. Thanks so much for the tips! I'll check them out and report back 

[Fixin Stuff]

Ok, results for Q3582, tested IN-circuit:
- B to E = .525V
- E to B = .514V
- B to C = .981V
- C to B = .536V

Doesn't seem very good? Unless readings are off due to it being in-circuit?

For Q7812 (full specs here: https://www.yic-electronics.com/datasheet/52/CMLD6001-TR.pdf and basic pic attached) also tested IN-circuit, results are:
- There's continuity between pins 1, 2, 5 & 6 (all drain)
- There's only 0.5ohms between the above pins and pin 4 (source) in resistance mode
- In diode mode, there's 0V between pin 1 and 4 in both directions
- From pin 3 to 4 there's .598V in diode mode, and OL in the other direction
- From pin 3 to all other pins is 0V in diode mode, and 0ohms in resistance mode

Please let me know your thoughts on these results 

[james_s]

Q3582 looks fine, those numbers sound reasonable at a glance.

For the other one that sounds suspect, there should not be zero ohms between the gate and any other pin, I think it's worth replacing that, or at least pull it out of circuit for further testing. You should be able to find a suitable mosfet to replace that for a dollar or so.

[Fixin Stuff]

Thanks for the follow up, James. You're a legend! I'll pull Q7812 out to test it again as you suggest and will report back 

[Fixin Stuff]

For the other one [Q7812] that sounds suspect, there should not be zero ohms between the gate and any other pin, I think it's worth replacing that, or at least pull it out of circuit for further testing. You should be able to find a suitable mosfet to replace that for a dollar or so.

I took Q7812 out of circuit to test. Used my gas soldering iron without a tip. It actually worked really well as a hot air station so I could release the chip using tweasers (first time I've tried this, and just as well as my electric soldering iron's element just failed)

Test results were:
- OL from pin 3 (gate) to everything, in diode mode, in any direction.
- 0v from pin 4 (source) to pins 1, 2, 5 & 6 (all drains) in diode mode, in any direction.
- 0.6 ohms between pin 4 and all drain pins.

Am I right that this means the gate is stuffed, and the source and drains are essentially shorted and uncontrolled, causing no control of the fan speed? 

[james_s]

It can be hard to say, mosfet gates are capacitive so you can actually charge one up and turn it on with your multimeter at which point S to D will show a short circuit or very close to it. You might try shorting all pins together, maybe use a piece of foil, then test between S and D.

[Fixin Stuff]

Hi James. Thanks for the ongoing help  I just shorted all of the pins on some foil a few times and really pressed it in to ensure a good connection. Resistance from S to D starts at 0 ohms and then gradually climbs to 0.4 ohms. Sometimes goes to 0.5/0.6 ohms but settles back at 0.4. So is it positively fooked? 

[james_s]

It sounds that way, I'd certainly try replacing it and see what happens, it's not an expensive part. You might scope the pad that connects to the G pin and see if you get a PWM signal there with the projector running.

[Fixin Stuff]

Thanks, James. Unfortunately I don't have a scope like the big boys  Some day!

Will order a replacement. Hardest thing seems to be identifying which type of inductor to use to replace L5701, which was actually the initial reason for this post 

From what I can tell so far, it's a multilayer surface mount type. All it says in the service manual (see previous posts) is it lists its Sanyo part number (seems like 2x numbers perhaps? unless the part number just takes up 2x lines). It also has the number 'L26B3470G' next to it. And it also says 'INDUCTOR,330 OHM P' (both with/without the P). Nut sure why it references Ohms and not Henrys?

When I search for either the Sanyo part number(s) or the other 'L26B3470G' number online, or on electronics companies websites (eg: Mouser/Digikey, and even EBAY) I don't see a part come up for these numbers.

Because I don't have the gear to take another identical inductor out of circuit and test the inductance rating, is there any other way to figure this out? Do I even need this inductor? (projector does work without it after all. I'd obviously prefer to have it if I can find a suitable one). Is there a generic rating I can use? 

Appreciate the assistance 

[james_s]

Isn't it just a ferrite bead? You could replace it with a piece of wire and it will work, if you want to do it right look for interference suppression beads in the right form factor, 330 ohm is much too high assuming that's the DC resistance.

Keep an eye out on the forum and other places, I know I've seen at least a couple of people giving away old scopes on here. An old analog scope is much better than no scope.

[Fixin Stuff]

Hi James. Yes, it's just a ferrite bead. I wasn't sure how important it is. I couldn't understand why it said 330 ohm next to it in the service manual. The other ones on the board measure 0 ohms across them. Perhaps it has the potential to resist current in a manner which is equivalent to 330 ohms of resistance in certain conditions or something? 

If I'm going to try and find a ferrite bead to replace it with, I'd prefer to use one within spec of the old one so it at least doesn't do any harm, or cause funky things to start happening. But if I can't properly identify it without a scope, then I guess I'll just leave it shorted to start with and see if it works ok without it.

I'd love to grab any kind of scope. I'm about to relocate inter-state, so trying to get rid of stuff right now. Can't wait till I'm more settled in the future so I can get a more-permanent workshop/lab set up for stuff like this.

I've ordered a replacement transistor. Says it could take a month to arrive (cos I didn't wanna pay 20x the cost of the chip for fast shipping, the joys of living in Australia). Will update you when it's arrived and installed 

[james_s]

A ferrite bead is just a piece of wire stuck through a hole in a piece of ferrite, they should have a very low DC resistance but to high frequency (like radio waves) they are deliberately lossy. They are generally used on wires supplying power to circuits that can produce electrical noise, the idea is that DC power flows through them but noise produced by the circuit doesn't get out and radiate from the wires. You probably won't notice any effect from one of them missing but if you were to bypass all of them you might find that the projector interferes with some devices that receive radio waves. 300 ohms is probably the impedance at a specific frequency, in this application it should not be critical at all, indeed if the original part is intact it's probably fine.

[Fixin Stuff]

My replacement fan control transistor arrived from China today and I installed it into the projector. I left the solder blob shorting where the burnt-out ferrite bead smd used to be, as it should work fine without it according to James_S

Turned it on and it seems to work just fine! Really pleased with the result, as it's my first successful component level repair    (even though it only needed to be fixed cos I broke it in the first place!) 

Wanted to say thanks to those who helped advise on the repair, particularly to James_S for all of his guidance and patience in explaining things to me 

Looking forward to fixin' more stuff in the future now