Need Help Identifying Zener Diode in Sony NS999ES DVD Player - diyAudio
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Old 24th November 2010, 02:59 AM   #1
rhing is offline rhing  United States
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Default Need Help Identifying Zener Diode in Sony NS999ES DVD Player

My Sony NS999ES DVD player won't power on. Checking out the switching regulator board, I found a blown electrolytic capacitor and glass encased Zener diode with scorch marks on the PCB underneath the diode. I replaced the blown cap, but I cannot determine the specs of the Zener diode. On the schematic, the only notation next to the diode in question, D302, is "HZ188P." I've searched everywhere and cannot find any reference to this marking. C402 was the blown cap I replaced.

Click the image to open in full size.


Unfortunately, Sony's service manual for this player provides a parts list for everything except this switching regulator board, ZSSR107G. Apparently, if something on the board goes bad, one is expected to buy the entire board from Sony for over $100. I'd rather just spend the few dollars to solder in a replacement Zener diode. Any help is greatly appreciated.
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Old 24th November 2010, 04:14 AM   #2
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I should have mentioned that the diode package has dimensions like a DO-35 (GLASS) molded glass body, and the marking on the diode body is "188."
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Old 24th November 2010, 07:13 AM   #3
Mooly is online now Mooly  United Kingdom
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The circuit image is to blurry to see. Can you rescan it or at least put a mark against the two parts. Is it the diode marked here... if so it looks like it's used as overvolts protection. A crowbar, that just fails short circuit if the PSU output increases. If so and the PSU is OK then it will work without it for test purposes. As a safety measure it should be fitted when all is OK.

I used to be repair tech and fixed countless SMPSU's over the years, loved working on them and identifying failure modes and so on. Most issues are down to dried out electrolytics so I would replace ALL on that board that in positions that pass high ripple currents. You need to at least do a quick "diode" check across the power devices and rectifiers to make sure non are short circuit. Any caps you replace should be of the same physical size and lead pitch and also of good quality. e.g. 105C temperature rating and specifically designed for SMPS applications.
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Old 24th November 2010, 01:09 PM   #4
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Hi Mooly,

Thank you for much for the prompt and thorough response. You did circle the correct Zener diode, D302, at the top of the schematic. C402, the 1500uF/16V capacitor is the cap circled with a question mark. This is the blown electrolytic cap that I replaced with a Panasonic FC 1500uF/25V (same lead spacing as blown Nichicon cap).

Please try this link for a higher resolution scan of the schematic.

http://img231.imageshack.us/img231/9...witchingre.jpg

Unfortunately, Flickr reduced the size/resolution of the image I uploaded.

I am a novice when it comes to these switching power supplies. Can you elaborate on doing a quick "diode" check across the power devices and rectifiers to make sure none are short circuited?

For reference, the output voltages are:

+3.3V, +5V, +11V, +8V and -8V.
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Old 24th November 2010, 01:33 PM   #5
Mooly is online now Mooly  United Kingdom
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That's a much better image.

If the PSU is non working then damage caused by the caps could literally be anything.

So you need to check IC101 pins D to S are not short. Same for D401, make sure it hasn't failed short circuit. Also check IP402 (circuit protector... a fuse) which should read short of course.

I would try and get the PSU working, then look to replace the other caps that are in stressed positions. I can scan and circle the ones to replace later. The fact that the zener is short means the rails have gone high. So is the failed cap the only issue, or, has something else happened and excess voltage has seen the cap off.

I'll have more time later to copy the image and mark what to check...


Be aware that the primary side caps can be charged to full mains potential even when off under certain conditions.
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Old 24th November 2010, 01:35 PM   #6
Mooly is online now Mooly  United Kingdom
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Forgot... diode check means using your DVM on "Diode" rather than just ohms range. It will show 0.00 or something very low if any device is short. A diode forward biased will read around 0.6 on the meter on that range. We are really checking for obvious shorts though.
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Old 24th November 2010, 01:49 PM   #7
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Very quickly here is what to change and check initially. The caps are all on the rails concerned with monitoring and feedback control. You should be OK with 47uf caps instead of 33uf. Even the 1500uf should be OK with 2200uf which are more common values.

I can't stress enough that the main failure mode of this type of PSU is caps. For what they cost I would replace all the electros.
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Old 24th November 2010, 03:03 PM   #8
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Wow! Thanks Mooly for the thorough repair and test information. I will definitely check the rectifiers and power devices in the circuit as you outlined.

I am still wondering about that Zener diode, D302, and what to replace it with. My thought is that it could be a BZX55C- series Zener diode, but I am not certain.
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Old 24th November 2010, 03:44 PM   #9
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Diodes used as crowbars tend to be unique as they not only have to fail short circuit but also withstand the current without literally shattering. An ordinary zener wouldn't survive. Remember though that to test and repair that the diode can be totally omitted.

Also as the PSU is self contained I would perhaps run it up on it's own (not connected to the DVD player) and tag a 60 watt mains filament bulb in series with the mains to limit any damage in case of some undiscovered fault.
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Old 24th November 2010, 03:53 PM   #10
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Advice well taken. Thanks.
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