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Meade DSI II - missing SMD parts....

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#1 DavidP

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Posted 27 November 2012 - 03:44 AM

Hi,
my DSI is broken :bawling: and I would need some help to identify the missing parts to get it up to work again :crazy:

The USB Connector went too far into the DSI and scraped off a few SMDs from the circuit board. The missing parts (I could not find them....) are between the USB Connector and the USB Microcontroller (Cypres CY7C68013-56PVC) and are labeled on the circuit board with:

R36, L2, C5, C8, C9 & C10

I'm not an expert in electronics but I guess I'm good enough to get the parts soldered back on if I get them identified/ordered.

Anyone out there who could help me to identify the values of the missing parts (resistor, capacitator and L???) either from measuring on their DSI or knowing about electronics?

Thanks, David

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#2 DavidP

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Posted 27 November 2012 - 03:59 AM

Maybe one more information:
The missing parts are going to the following pins on the microcontroller (description taken from the datasheet of the mc):
Label - Pin - Description

R36 - Pin5 - CLKOUT
C9 - Pin6 - VCC
L2 & C10 - Pin10 - AVCC
C8 - Pin14 - VCC
C5 - Pin18 - VCC

The datasheet is to big to attach it here but it can be found i.e. here

#3 Geo.

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Posted 27 November 2012 - 10:03 PM

Problem with the small SMD caps is that they aren't marked. At the the factory the robot grabs them from the tape and places them on the PCB. I have a good Fluke DMM, but I usually can't get an accurate reading on them, range doesn't go down that far. I'd go to the Electronic Goldmine and get some "Gold Paks" of SMD caps and resistors.

"We don’t take the time to sort this 100% prime material as it comes in. We just place it in 55 gal drums. Over 1,000 pieces [fit] in a 2" x 3" zip close bag!"

Paks start at $2.50. I only see one SMD inductor, but at $0.21 what the heck.

L2 - Pin10 - AVCC - A guess this is the power supply for the chip. L2, an inductor, is usually in the power feed. See if you can trace it back to USB pin 1.

C8 - Pin14 - VCC
C5 - Pin18 - VCC
C9 - Pin6 - VCC
C10 - Pin10 - AVCC

These ceramic caps are most likely decoupling capacitors. They decouple one part of an electrical circuit from another. Noise caused by other circuit elements is shunted through the capacitor to ground, reducing the effect it has on the rest of the circuit. Caps are rated on their capacitance and the voltage they can handle. Ceramics usually can handle high voltages, but have low capacities. To simplify assembly the circuit design will attempt to use similar types of components. So I'd try to match the caps you see on the circuit for size and color. If in doubt go with the larger size. Oversizing a cap rarely causes a problem.

R36 - Pin5 - CLKOUT Too bad this went missing as it's the only resistor. Again look around the board and see what they are using. Start with the highest value.

Placing SMDs on the board is hard but doable. A tempertaure controlled iron is best. You need a sharp point. In tight spaces super glue a tooth pick to the component to get it into position. Pick up some solder with the iron and bridge the component and the board. Should only take a second or two to get good flow. Goldmine has some SMD practice PCBs you may want to try first. Good luck!

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#4 DavidP

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Posted 28 November 2012 - 05:07 PM

Hi George, thanks for helping me :)

L2 goes on one side to C9 / micro controller pin 6 and on the other side to C10 / micro controller pin 10, but not to USB pin 1. See attachment for a better overview.

All other parts, R36, C9, C10, C8 & C5 are hooked up on one side to ground via USB pin 4.

I checked the various resistors on the board and the highest value seemed to be 9.94 k Ohm. In fact, one resistor sitting between micro controller pin 21 and GND has exactly this value. Does this high resistance value sound right?

I checked out Goldmine and would order item A20456S for the inductor. For the caps / resistor, would you recommend item GP37 (mix of caps & resistors) or G3118 caps and GP38 resistors only?

Thanks for the advices on how to solder the SMDs. In particular the tooth pick "trick" sounds great :D I might have to get a sharper solder point as it looks very narrow now that I'm going to work on it......

David

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#5 orlyandico

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Posted 28 November 2012 - 06:29 PM

I'm guessing you can use the same value for all the caps. Those look like power supply decoupling capacitors to me, because they all go to ground. 100nF is a typical value.

The resistor on CLKOUT seems to be a pull-down. The USB specification is 15K pull-down for downstream ports. 10K would probably work just fine.

The inductor is probably a "boost inductor" and a typical value is 22 uH. That it is connected between VCC and AVCC bolsters my guess. Cypress has an application note where they say you need a boost inductor rated at least 750 mA. the common 22 uH ones are 1.2A so should be fine.

disclaimer: I got all the above information from a 10-minute google search (i'm really good at google searching). Although i am an electrical engineer and this information is to the best of my knowledge, i take no liability for any potential smoke generation :grin:

#6 DavidP

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Posted 30 November 2012 - 02:13 PM

disclaimer:.....


LOL - I'm more afraid of my soldering skills messing it up :crazy:

I ordered the parts and will report back after the surgery....

#7 Geo.

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Posted 02 December 2012 - 04:00 PM

Orly, look at the component mounting points. Yes, there is nothing there, but nor does it look like there ever was. No torn up traces. No indication of component adhesive. As these are sold with a color and a mono CCDs I would imagine that not all the component locations are used in both types. What do you think?

#8 orlyandico

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Posted 02 December 2012 - 07:50 PM

Hi George,

The parts are there - apparently Meade didn't change the USB design between the I and II. Here's a photo of the same spot on the PCB for my DSI I Pro.

I guessed right on the resistor (10K) but the rest of the parts are unreadable.

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