Need a discontinued HV diode

Discussion in 'General Electronics Chat' started by adam555, Dec 17, 2015.

  1. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    Hi,

    I need a discontinued high voltage rectifying diode (Y10GA), or equivalent, and can't find them anywhere. I even asked Hitachi, which is the brand of the device I need it for, and looked in an online service for electronic suppliers (seekIC), but the best I could get was someone from Asia asking me for $60 plus $35 in P&P; which is practically what I paid for the oscilloscope I'm trying to repair, and I don't really trust the seller. The rest that answered say they can't find any.

    I would appreciate if anyone could direct me towards a retailer with this item, or recommend an equivalent part. The specs of Y10GA are:

    I(O) Max.(A) Output Current : 5.0
    V(RRM)(V) Rep.Pk.Rev. Voltage : 6.0k
    I(FSM) Max.(A) Pk.Fwd.Sur.Cur. : 500m
    V(FM) Max.(V) Forward Voltage : 22
    @I(FM) (A) (Test Condition) : 5.0m
    I(RM) Max.(A) Reverse Current : 4.0u
    @V(R) (V)(Test Condition) : 6.0k
    Maximum Operating Temp (шC) : 120х
    Package Style : Axial-11
    Mounting Style : T

    Thanks in advance for your help,
     
  2. JohnInTX

    Moderator

    Jun 26, 2012
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    Have you tried contacting the manufacturer of the scope or an authorized service outlet? They usually have the same or equivalent parts.
     
  3. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    Tried Hitachi with no luck, but didn't look for an authorised service.

    I'll try to find one. Thanks.
     
  4. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    Tried the 5 authorised services around this part of the country, and either they specialise in particular devices that have nothing to do with oscilloscopes, or the part is so old that they can't even find it on their catalogues.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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  6. Lestraveled

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  7. KeepItSimpleStupid

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  8. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    You're right, there's a mistake in that datasheet; which I copied and pasted here. These are specs from Hitachi; the other specs were from American Microsemiconductor.

    Search: Y10GA
    Silicon Rectifier
    V(RRM)(V) Rep.Pk.Rev. Voltage=6.0k
    I(RM) Max.(A) Reverse Current=4.0u
    @V(R) (V)(Test Condition)=6.0k
    I(FSM) Max.(A) Pk.Fwd.Sur.Cur.=500m
    V(FM) Max.(V) Forward Voltage=22
    @I(FM) (A) (Test Condition)=5.0m
    I(O) Max.(A) Output Current=5.0
    Status=Discontinued
    Package=Axial-11
    Military=N

    I'll have a look in all the places proposed, and get back to you. Any more sources are welcome too; I'll check them all.
     
  9. Lestraveled

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  10. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    HVStuff was the first place I looked. That diode has a voltage drop of 34V. The one I need has 22V.

    The right drop voltage seem to be essential. As a matter of fact the diode kind of still works, but it must be damaged because I took it out and measured the 5V voltage drop at 5mA.

    I found a better equivalent in HVStuff. This one: 5mA 6kV 100nS High Voltage Diode HV Rectifier High Frequency
    But the specs are not exactly the same. For example: voltage drop is different and it doesn't state the rest.
     
  11. alfacliff

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    Dec 13, 2013
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  12. Lestraveled

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    At these voltages the difference in a 20 verses a 22 volt drop is insignificant.
     
  13. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    I was not sure if the differences between those 2 diodes would have any undesirable effect, so I'd rather ask. The diode is for a Hitachi V-552 oscilloscope with a dim trace. I checked most of the components on the HV circuit (except the high voltages) and couldn't find anything else wrong, but the 5V drop voltage at 5mA on the Y10GA instead of the 22V specified in the specs.

    Can anyone look at this diagram and tell me if the Y10GA could be the problem, and if the 20V substitute from HVStuff will work?

    Hitachi V-552 Diagrams (Y10GA).jpg
     
  14. ian field

    Distinguished Member

    Oct 27, 2012
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    Couldn't find any mention of Trr in that list - could be important if it rectifies a scan derived supply in a TV or monitor.

    If I read that right; The Vf is 22V - I couldn't make out any decimal point, that means its multiple stacked junctions.

    You could assemble a series chain of lower voltage diodes, but you either have to use controlled-avalanche types or put a leakage swamping resistor in parallel with each diode in the chain.
     
  15. Lestraveled

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    Did you measure the -1650 voltage or the +10KV voltage?
     
  16. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    No, I couldn't. I only measured the low voltages, as I don't have a HV probe, and all of them were right.

    Going with anything else than replacing the diode with the same one or a close match looks too risky for me, as I don't have much experience at this. I'm even doubting whether or not to buy that close equivalent if I can't find an exact match. I'm a bit afraid of damaging it any further, as the way it is right now -even with a dim trace- works well enough.
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
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    Years ago I replaced all the selenium stacks in a scope EHT multiplier with silicon TV efficiency diodes so that the lower forward drops compensated for failing beam current.

    If I'd done that on a scope with normal beam current - the stronger electron beam would have taken more force to deflect. That means it would affect the calibration. As it was, it just brought the beam a bit closer to where it should have been in the first place - it was a scope I'd rescued from the tip, so I only used it to examine wave shapes. Voltage and time period were measured with more appropriate instruments.

    On a 6kV stick - the difference between Vf of 22 and 30V won't even be background noise compared to the wear and tear on the CRT cathode since it was new.
     
  18. N11778

    Member

    Dec 4, 2015
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    Quote: adam555 "as the way it is right now -even with a dim trace- works well enough."

    If its just a dim trace Not Blurry and works, can you put it on a variac and boost the filliment voltage in the crt.
    If you dont have a variac put a 12v transformer output in series with the 120v and see if it gets brighter.
    132 volts should not hurt anything. Sounds like the coating on the Crt Cathode mite be getting tired.
    Can you post the entire diagram? Some of the older scopes were not very bright to begin with.
    Make sure to test the 120 voltage first to see if you have the transformer phased with the power line.
    if its not you will read aprox 108v , if so reverse the wires on the transformer output.
     
  19. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    I don't feel comfortable enough to attach a variac or the 120V transformer; I'm just a beginner. But I measured all the voltages, including the 120V, and couldn't find anything wrong. The only thing I could find was that diode, which someone recommended me to check.

    I also don't think it's the crt cathode, as at the beginning the dimming went on and off suddenly. It was like that for a few months, and then it just stayed dim until now.

    I'm attaching the whole diagram for the HV and Z-amp, and the HV section with the Y10GA marked.

    Hitachi V-552 Diagrams (Y10GA).jpg HV and Z-Amp.jpg

    But then, do you think that the 5V drop on the HV diode instead of the 22V could be the cause of the problem?
     
    Last edited: Dec 19, 2015
  20. ian field

    Distinguished Member

    Oct 27, 2012
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    As long as that's a mains transformer running at 60Hz, you can just string standard recovery diodes in series. 1N4007 are 1000V, so 6 in series will do - but an extra one for luck wouldn't hurt.

    You can use UF4007 diodes if its a high frequency SMPSU.

    At those sort of voltages, the risk of external flashover is greater than diode breakdown. But reverse leakage can vary quite a bit between diodes - the one with the least leakage will get more than its fair share of the voltage. The usual practice is to swamp the leakage with a parallel resistor on each diode - I'd suggest 4M7.

    The lower Vf is highly unlikely to cause a problem, but I'd insert a 1k resistor between the diode and the first capacitor. It sounds like the original diode failed open circuit - otherwise it could have cooked the transformer. A chain of 4007s could fail short, a resistor in series before the first capacitor provides a weak link that can blow first.
     
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