• High Speed HV power supply

    From trader...@gmail.com@traderonev10@gmail.com to rec.games.pinball on Thursday, September 24, 2020 18:47:07
    From Newsgroup: rec.games.pinball

    Having a problem with the HV section of a High Speed power supply, specifically the negative voltage out. I’m seeing about -54vdc on the -100v out line and 104vdc on the +100v out line. Please read my entire post before responding. Also, please do not say “rebuild the entire HV section” as that will not help me with this problem given what I’ve already done.
    I have 90vac being generated from a variac connected to the fuse clip for the HV fuse and TP2 bypassing the connectors as a source of the problem. When I fire up the variac I measure -122vdc at the anode of ZR3 and -118vdc on the cathode end of ZR3. I measure the same -118vdc at the base of Q4 but at the emitter of Q4 I only measure about -54.5vdc instead of about -100vdc. Replacing Q4 with a new 2N5551 results in no change to this voltage. Replacing Q3 with a new MJE15031 also results in no change to the voltage. I tested R3, R4, R6, C3 and ZR4 and all test fine. There is no apparent work that has been done previously to the board other than the connectors which I have bypassed.
    What am I missing?
    viperrwk
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  • From pinw...@bellsouth.net@pinworks@bellsouth.net to rec.games.pinball on Sunday, September 27, 2020 07:12:34
    From Newsgroup: rec.games.pinball

    On Thursday, September 24, 2020 at 9:47:17 PM UTC-4, trader...@gmail.com wrote:
    Having a problem with the HV section of a High Speed power supply, specifically the negative voltage out. I’m seeing about -54vdc on the -100v out line and 104vdc on the +100v out line. Please read my entire post before responding. Also, please do not say “rebuild the entire HV section” as that will not help me with this problem given what I’ve already done.

    I have 90vac being generated from a variac connected to the fuse clip for the HV fuse and TP2 bypassing the connectors as a source of the problem. When I fire up the variac I measure -122vdc at the anode of ZR3 and -118vdc on the cathode end of ZR3. I measure the same -118vdc at the base of Q4 but at the emitter of Q4 I only measure about -54.5vdc instead of about -100vdc. Replacing Q4 with a new 2N5551 results in no change to this voltage. Replacing Q3 with a new MJE15031 also results in no change to the voltage. I tested R3, R4, R6, C3 and ZR4 and all test fine. There is no apparent work that has been done previously to the board other than the connectors which I have bypassed.

    What am I missing?

    viperrwk
    How did you test ZR4? That is a Zener Diode. The only real way to test one is under load and I think yours is failing. That would account for the lower voltage. I would replace it first.
    Good Luck
    Pinworks
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  • From trader...@gmail.com@traderonev10@gmail.com to rec.games.pinball on Friday, October 02, 2020 08:39:03
    From Newsgroup: rec.games.pinball

    On Sunday, September 27, 2020 at 10:12:42 AM UTC-4, pinw...@bellsouth.net wrote:
    On Thursday, September 24, 2020 at 9:47:17 PM UTC-4, trader...@gmail.com wrote:
    Having a problem with the HV section of a High Speed power supply, specifically the negative voltage out. I’m seeing about -54vdc on the -100v out line and 104vdc on the +100v out line. Please read my entire post before responding. Also, please do not say “rebuild the entire HV section” as that will not help me with this problem given what I’ve already done.

    I have 90vac being generated from a variac connected to the fuse clip for the HV fuse and TP2 bypassing the connectors as a source of the problem. When I fire up the variac I measure -122vdc at the anode of ZR3 and -118vdc on the cathode end of ZR3. I measure the same -118vdc at the base of Q4 but at the emitter of Q4 I only measure about -54.5vdc instead of about -100vdc. Replacing Q4 with a new 2N5551 results in no change to this voltage. Replacing Q3 with a new MJE15031 also results in no change to the voltage. I tested R3, R4, R6, C3 and ZR4 and all test fine. There is no apparent work that has been done previously to the board other than the connectors which I have bypassed.

    What am I missing?

    viperrwk
    How did you test ZR4? That is a Zener Diode. The only real way to test one is under load and I think yours is failing. That would account for the lower voltage. I would replace it first.

    Good Luck
    Pinworks
    Thanks. In the end the problem was D4. At first I didn't suspect D4 because I was getting 122v at the anode of ZR3. Additionally, I had a mental block because when I first went to check D4 I was actually checking D3 as D3 is located under the negative HV section and D4 is located under the positive HV section. I had even gone so far as to remove D3 to test it out of circuit and since it was fine believed my problem was elsewhere. Yes I looked at the board layout and yes saw where D3 and D4 were but obviously age is catching up with me and I reversed the two when first diagnosing the problem.
    Once I verified the correct voltages I wound up replacing ZR2 and ZR4 anyway as the displays in the machine this power supply is in could handle the lower voltages.
    There are those who say why didn't you simply shotgun the entire negative section anyway and be done with it, esp since you were changing ZR2 and ZR4 anyway? Answers:
    1 - I wanted to know specifically what was causing this problem.
    2 - When you spend the vast majority of your time at home you need other mental exercises to keep you entertained.
    3 - I had the time for this exploration.
    For most people, the best answer when dealing with HV problems is simply shotgun the entire HV section. That answer hasn't changed.
    viperrwk
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