Wrong Components?

Wrong Components?

Postby AllanW » Sat May 09, 2015 3:46 pm

I am putting together this kit and have run into a couple of problems.

I have fitted the ceramic caps but the only value left for the C2 position is 220pF when according to the instructions it should be 330pF. Will it be a problem if I fit the 220pF capacitor?

The two transistors provided were marked up as "S8550 D128" and "S8550 D331" - I assume that these are the same spec transistor and one of them has been provided by mistake when it should have been a 9014 for position Q2?

Please help!
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Re: Wrong Components?

Postby jye1 » Sun May 10, 2015 12:16 am

Containing two S8550 transistors was a mistake. If you have any general purpose NPN transistor you can use it for 9014. Otherwise, please contact us at jyetech@163.com. We will send you free replacement.

For C2 220pF is ok. The value for the cap is not very critical. Initially this cap was specified 220pf as indicated in schematic. Later it was found 330pF was slightly better and we modified the BOM. New shipment should come with 330pF.
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Re: Wrong Components?

Postby AllanW » Sun May 10, 2015 6:27 pm

Thank you for the prompt reply. Will see if I have a suitable transistor about. :D
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Re: Wrong Components?

Postby gcwills » Tue May 12, 2015 7:36 am

Firstly, thanks for a great design.

However, like Allan, my kit had the wrong components - specifically the transistor for Q2 (9014) - a 9012 PNP was supplied. I assumed that it was a suitable substitute when assembling the unit, but at first power up, Q1 was overheating badly. Some time checking the unit identified the incorrect transistor, but unfortunately Q1 was damaged with leaky BE.

Replacing the faulty or incorrect transistors got the unit working, but there is an issue that needs attention. The buck converter output is way too high - your notes say around 8-9V, but my unit shows 16V+ at TP25. The only way to reduce this is to reduce the main power volts to 7V or so - not really a solution.

L2 has been tested and all ok. I notice that there appears to be a feedback network around R41 and R42 - do these alter the mark/space ratio of VGEN?

Any help would be appreciated.

Grant
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Re: Wrong Components?

Postby gcwills » Wed May 13, 2015 9:01 am

Hi again,
Have just located the problem with excessive output from the buck converter. The kit was supplied with a 0.1mH (100uH) choke for L2 instead of the 1mH that it should have been.
This low value inductor was responsible for the high negative supply voltage from the buck converter.
Grant
Last edited by gcwills on Thu May 28, 2015 11:27 pm, edited 1 time in total.
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Re: Wrong Components?

Postby jye1 » Wed May 13, 2015 10:45 pm

Sorry to see again incorrect component was shipped. But this one is different from that fount by AllenW where duplicated 8550 was sent which apparently was a manufacture mistake. The S9012 was likely already mixed in supplies. This is very hard to detect since it is almost impossible to all components one by one. But we are glad to provide replacement if mistake is reported and proofed.

For the incorrect L2 there was another possibility that the inductor was partially shorted inside by high heat when S9012 was used. Please contact JYE Tech at jyetech@163.com for a replacement.

R41 and R42 were intended to monitoring of V-. But current firmware does not support this yet.
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Re: Wrong Components?

Postby gcwills » Thu May 28, 2015 1:51 am

Just wanted to update my previous posts to say the discrepancies with my kit were in fact due to the kit being a fake/counterfeit DSO138 kit from ebay.

For those concerned about legitimacy of their kit, it appears the tell tale signs of a fake are:
1. thin/poor screen printing on the pcb
2. pin 19 ID on the LCD panel being close to the line
3. R38 is marked twice on the pcb
4. no documentation with the kit
5. C2 is supplied with a 220pf rather than a 330pf
6. Q2 is supplied as a 9012 PNP rather than the 9014 NPN required
7. L2 is supplied as a 0.1mH (100uH) inductor rather than the correct 1mH - this causes the negative output from the buck converter across C24 being way too high (about -18v)

The good news is that if you have a fake kit, it can be made to work by replacing the 9012 with a 9014 (or any general purpose small signal NPN) and replacing the incorrect 0.1mH inductor with a 1mH inductor with a current rating of a least 500mA. You may need to replace Q1 (8550) if it has been damaged by the incorrect Q2 (9012)

Cheers!
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Re: Wrong Components?

Postby centurion » Tue Jun 23, 2015 8:20 am

I just got this kit. only the transistor Q2 9014, but still burned Q1
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Re: Wrong Components?

Postby dennisS » Fri Jul 24, 2015 3:34 am

Unfortunately, I also purchased a counterfeit kit without my knowledge, and have exactly the issues listed above. The problem is I can't find anyone that carries the 1mH @ 0.5A or 1A radial inductor. Anyone find a source for these?

I saw some on eBay, but they don't list the current rating and emailing them was a dead end. I contacted eBay about how they can still knowingly sell these counterfeit kits, but apparently they don't seem to care.

I tried Sparkfun, Jameco, Mouser, Digikey.. no luck.
Any help with a part number or source would be appreciated! thanks!
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Re: Wrong Components?

Postby davef » Fri Jul 24, 2015 4:37 am

If you get really stuck I tried replacing the whole switcher and -5V regulator with this http://www.jyetech.com/forum/viewtopic.php?f=18&t=505
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