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line voltage 7704a

jerry massengale Member Profile All Messages By This Member #82356 Hi, I have a 7704A power supply that will not work at normal line voltage but seems happy and regulated at 70 to 100 volts in. Zeners and caps in the inverter have been rechecked and verified okay. 2 inverter chips(-02s) work the same. The 54V adjust is right on as is the -50V adjust. The voltage select looks okay. Ideas?
Albert #82357 Does this happen in normal use in the 'scope, independent of number of plugins? [I ask because of your minimum load question some days ago.] Does "not work" mean the supply falls back in tick mode? Many components at the primary side have to withstand higher voltages when the line voltage is increased. Failure of the big caps would have a catastrophic effect I guess. Perhaps failure of a switching transistor might stop the inverter quick enough to prevent further damage? Albert toggle quoted message Show quoted text --- In TekScopes@..., "hojo3008" <j_massengale@...> wrote: Hi, I have a 7704A power supply that will not work at normal line voltage but seems happy and regulated at 70 to 100 volts in. Zeners and caps in the inverter have been rechecked and verified okay. 2 inverter chips(-02s) work the same. The 54V adjust is right on as is the -50V adjust. The voltage select looks okay. Ideas?
jerry massengale Member Profile All Messages By This Member #82358 Hi Albert, I am using a minimum load I just built. The power supply is out of the mainframe on the bench. I have two power supplies. Both show tick mode at normal voltage. I have been fighting learning some things the hard way. VR3129 on my schematic shows 15V but is a 20V 1n968. R3129 is connected like the schematic thanks to being rerouted with an etch cut and jumper that corrects a layout error. One end of R3129 dangles in the breeze with one end not connected as laid out. One of my power supplies work at 70 to 100v and r3129 is not corrected. The other will not work at any voltage and does have r3129 in the circuit like the schematic. Right now neither power supply is trying to come up and I am too tired and frsutrated to figure out why. Maybe tomorrow. jerry Jerry Massengale toggle quoted message Show quoted text -----Original Message----- From: Albert To: TekScopes Sent: Tue, Oct 23, 2012 1:36 pm Subject: [TekScopes] Re: line voltage 7704a ? Does this happen in normal use in the 'scope, independent of number of plugins? [I ask because of your minimum load question some days ago.] Does "not work" mean the supply falls back in tick mode? Many components at the primary side have to withstand higher voltages when the line voltage is increased. Failure of the big caps would have a catastrophic effect I guess. Perhaps failure of a switching transistor might stop the inverter quick enough to prevent further damage? Albert --- In TekScopes@..., "hojo3008" wrote: > > Hi, > > I have a 7704A power supply that will not work at normal line voltage but seems happy and regulated at 70 to 100 volts in. Zeners and caps in the inverter have been rechecked and verified okay. 2 inverter chips(-02s) work the same. The 54V adjust is right on as is the -50V adjust. The voltage select looks okay. Ideas? >
Albert #82359 Hi Jerry, VR3129 is 20 V (1N968B) as from S/N B06000, see manual from Tekwiki for instance. I don't remember anything "strange" with R3129. I don't know what effect a missing R3129 has on the IC. With -2 V missing, the sense functions (and more) might get corrupted. I think your minimum load is not large enough. Then at normal line voltage the maximal dead time the IC can generate after each switch is still not enough to prevent the +54 V going higher than that. I think the minimum loads are minimum for the LV regulators to operate properly (w.r.t. load and line regulation). The total of all those minima might still be too little load for the inverter. Albert toggle quoted message Show quoted text I am using a minimum load I just built. The power supply is out of the mainframe on the bench. I have two power supplies. Both show tick mode at normal voltage. I have been fighting learning some things the hard way. VR3129 on my schematic shows 15V but is a 20V 1n968. R3129 is connected like the schematic thanks to being rerouted with an etch cut and jumper that corrects a layout error. One end of R3129 dangles in the breeze with one end not connected as laid out. One of my power supplies work at 70 to 100v and r3129 is not corrected. The other will not work at any voltage and does have r3129 in the circuit like the schematic. Right now neither power supply is trying to come up and I am too tired and frsutrated to figure out why. Maybe tomorrow. jerry Jerry Massengale Does this happen in normal use in the 'scope, independent of number of plugins? [I ask because of your minimum load question some days ago.] Does "not work" mean the supply falls back in tick mode? --- Albert I have a 7704A power supply that will not work at normal line voltage but seems happy and regulated at 70 to 100 volts in. Zeners and caps in the inverter have been rechecked and verified okay. 2 inverter chips(-02s) work the same. The 54V adjust is right on as is the -50V adjust. The voltage select looks okay. Ideas?
David Hess Member Profile All Messages By This Member #82360 Are you equipped to make safe primary side oscilloscope measurements? When you say you checked the primary side zener diodes, do you mean all of them including VR3059? Did you check them for leakage? Besides measuring the voltages at the various pins of U3105 to see if it is initiating the shutdown, I would check the circuit around Q3052 and see if it is triggering at normal AC line voltage. What resonate frequency is the inverter operating at? Maybe there is a problem with L3037 or C3037. On Tue, 23 Oct 2012 16:49:02 -0000, "hojo3008" <j_massengale@...> wrote: Hi, I have a 7704A power supply that will not work at normal line voltage but seems happy and regulated at 70 to 100 volts in. Zeners and caps in the inverter have been rechecked and verified okay. 2 inverter chips(-02s) work the same. The 54V adjust is right on as is the -50V adjust. The voltage select looks okay. Ideas?
Albert #82363 Hi David, VR3059 and Q3052 can cause troubles, but how would you explain that a failure there causes the inverter to stop (fall back in tick mode) when the line voltage is increased from too low to normal? Albert toggle quoted message Show quoted text --- In TekScopes@..., David <davidwhess@...> wrote: Are you equipped to make safe primary side oscilloscope measurements? When you say you checked the primary side zener diodes, do you mean all of them including VR3059? Did you check them for leakage? Besides measuring the voltages at the various pins of U3105 to see if it is initiating the shutdown, I would check the circuit around Q3052 and see if it is triggering at normal AC line voltage. What resonate frequency is the inverter operating at? Maybe there is a problem with L3037 or C3037. On Tue, 23 Oct 2012 16:49:02 -0000, "hojo3008" <j_massengale@...> wrote: Hi, I have a 7704A power supply that will not work at normal line voltage but seems happy and regulated at 70 to 100 volts in. Zeners and caps in the inverter have been rechecked and verified okay. 2 inverter chips(-02s) work the same. The 54V adjust is right on as is the -50V adjust. The voltage select looks okay. Ideas?
Tom Miller Member Profile All Messages By This Member #82365 开云体育 I had one where the VR3059 fired at 80 volts and caused the PS to shutdown. You might check it on a curve tracer. ? Tom ? toggle quoted message Show quoted text ----- Original Message ----- From: Albert To: TekScopes@... Sent: Tuesday, October 23, 2012 4:53 PM Subject: [TekScopes] Re: line voltage 7704a ? Hi David, VR3059 and Q3052 can cause troubles, but how would you explain that a failure there causes the inverter to stop (fall back in tick mode) when the line voltage is increased from too low to normal? Albert --- In TekScopes@..., David wrote: > > Are you equipped to make safe primary side oscilloscope measurements? > > When you say you checked the primary side zener diodes, do you mean > all of them including VR3059? Did you check them for leakage? > > Besides measuring the voltages at the various pins of U3105 to see if > it is initiating the shutdown, I would check the circuit around Q3052 > and see if it is triggering at normal AC line voltage. > > What resonate frequency is the inverter operating at? Maybe there is > a problem with L3037 or C3037. > > On Tue, 23 Oct 2012 16:49:02 -0000, "hojo3008" > wrote: > > >Hi, > > > >I have a 7704A power supply that will not work at normal line voltage but seems happy and regulated at 70 to 100 volts in. Zeners and caps in the inverter have been rechecked and verified okay. 2 inverter chips(-02s) work the same. The 54V adjust is right on as is the -50V adjust. The voltage select looks okay. Ideas? >
David Hess Member Profile All Messages By This Member #82368 I was thinking that the Over-Voltage Stop circuit built around Q3052 is triggering at a lower primary voltage than it should be or the R3034/R3049 ratio is off. I notice that Tektronix fiddled with the network that drives Q3052 in later oscilloscope models. I suppose one could temporarily disable that circuit by removing VR3059 but I would replace it with a higher voltage zener instead. If R3034 was low or R3049 was high, that could cause the problem. On Tue, 23 Oct 2012 20:53:41 -0000, "Albert" <aodiversen@...> wrote: Hi David, VR3059 and Q3052 can cause troubles, but how would you explain that a failure there causes the inverter to stop (fall back in tick mode) when the line voltage is increased from too low to normal? Albert --- In TekScopes@..., David <davidwhess@...> wrote: Are you equipped to make safe primary side oscilloscope measurements? When you say you checked the primary side zener diodes, do you mean all of them including VR3059? Did you check them for leakage? Besides measuring the voltages at the various pins of U3105 to see if it is initiating the shutdown, I would check the circuit around Q3052 and see if it is triggering at normal AC line voltage. What resonate frequency is the inverter operating at? Maybe there is a problem with L3037 or C3037. On Tue, 23 Oct 2012 16:49:02 -0000, "hojo3008" <j_massengale@...> wrote: Hi, I have a 7704A power supply that will not work at normal line voltage but seems happy and regulated at 70 to 100 volts in. Zeners and caps in the inverter have been rechecked and verified okay. 2 inverter chips(-02s) work the same. The 54V adjust is right on as is the -50V adjust. The voltage select looks okay. Ideas?
jerry massengale Member Profile All Messages By This Member #82371 Hi, Thanks to all the good advice. You guys are right on. Murphy was playing with me a bit. The 7.5ohm thermistor in the primary was never very pretty but was in one piece. It finally came apart and caused my the new problem about not powering up. I kept missing it as I had checked it earlier and thought it was good. Maybe my rough handling broke it. This was the unit that would run with low voltage. I later found that Cr3059(which is marked cr54 in the pix) was a 1n986, a 110V zener, which was likely causing the early shutdown. I am ordering 200 120v zeners if someone wants one or two. There are probably more 110v zeners lurking about. I had a used 7.5ohm thermistor but no 120v zeners. This unit does not have the corrected R3139 connection which may add to the conspiracy to frustrate me. The other unit with tick mode at all voltages has a Q3034(2n6300) with an emitter to collector short AND an open CR3059. Maybe the CR3059 got zapped when Q3034 got zapped. My minimum load was constructed with the following values taken from Hakan's recipe for a 7904 min-load. -50v 620Ω 10W +5v 15ohm 5W -15v 18ohm 22W +50v 220ohm 15W +15v 15ohm 30W lites 15ohm 15W I think it is okay but I have no load on the HV drives. I have not found a good replacement for the 2n6300. Qservice has them for $10 which is the best price I have found. The tek semi book list the 2n6300 as a 650V part? I have found 2n6307s for $4 each that I suspect would work okay. Opinions? a low res pix of the load follows in another email Jerry Massengale toggle quoted message Show quoted text -----Original Message----- From: David To: TekScopes Sent: Tue, Oct 23, 2012 4:42 pm Subject: Re: [TekScopes] Re: line voltage 7704a ? I was thinking that the Over-Voltage Stop circuit built around Q3052 is triggering at a lower primary voltage than it should be or the R3034/R3049 ratio is off. I notice that Tektronix fiddled with the network that drives Q3052 in later oscilloscope models. I suppose one could temporarily disable that circuit by removing VR3059 but I would replace it with a higher voltage zener instead. If R3034 was low or R3049 was high, that could cause the problem. On Tue, 23 Oct 2012 20:53:41 -0000, "Albert" <aodiversen@...> wrote: >Hi David, > >VR3059 and Q3052 can cause troubles, but how would you explain that a failure there causes the inverter to stop (fall back in tick mode) when the line voltage is increased from too low to normal? > >Albert > >--- In TekScopes@..., David wrote: >> >> Are you equipped to make safe primary side oscilloscope measurements? >> >> When you say you checked the primary side zener diodes, do you mean >> all of them including VR3059? Did you check them for leakage? >> >> Besides measuring the voltages at the various pins of U3105 to see if >> it is initiating the shutdown, I would check the circuit around Q3052 >> and see if it is triggering at normal AC line voltage. >> >> What resonate frequency is the inverter operating at? Maybe there is >> a problem with L3037 or C3037. >> >> On Tue, 23 Oct 2012 16:49:02 -0000, "hojo3008" >> wrote: >> >> >Hi, >> > >> >I have a 7704A power supply that will not work at normal line voltage but seems happy and regulated at 70 to 100 volts in. Zeners and caps in the inverter have been rechecked and verified okay. 2 inverter chips(-02s) work the same. The 54V adjust is right on as is the -50V adjust. The voltage select looks okay. Ideas? >> >
David Hess Member Profile All Messages By This Member #82384 Compared to the 2N6308, the 2N6307 Vcbo is 600 instead of 700 volts and the Vce is 300 instead of 350 but I suspect it will still work. Alternatively Mouser has the 2N6545 for $4.14 and the BUX48A for $4.53. On Tue, 23 Oct 2012 20:15:33 -0400 (EDT), jerry massengale <j_massengale@...> wrote: I have not found a good replacement for the 2n6300. Qservice has them for $10 which is the best price I have found. The tek semi book list the 2n6300 as a 650V part? I have found 2n6307s for $4 each that I suspect would work okay. Opinions? Jerry Massengale
jerry massengale Member Profile All Messages By This Member #82385 Hi, I made a mistake in my earlier mail, it was the 2n6308 that I ordered. I bought 4 for $29 including shipping. I also bought 100 bav19s for $15.25. Jerry Massengale toggle quoted message Show quoted text -----Original Message----- From: David To: TekScopes Sent: Tue, Oct 23, 2012 11:18 pm Subject: Re: [TekScopes] Re: line voltage 7704a ? Compared to the 2N6308, the 2N6307 Vcbo is 600 instead of 700 volts and the Vce is 300 instead of 350 but I suspect it will still work. Alternatively Mouser has the 2N6545 for $4.14 and the BUX48A for $4.53. On Tue, 23 Oct 2012 20:15:33 -0400 (EDT), jerry massengale <j_massengale@...> wrote: >I have not found a good replacement for the 2n6300. Qservice has them for $10 which is the best price I have found. The tek semi book list the 2n6300 as a 650V part? I have found 2n6307s for $4 each that I suspect would work okay. Opinions? > >Jerry Massengale
David C. Partridge Member Profile All Messages By This Member #82389 I can definitely confirm the BUX48A is a robust substitute. Regards, David Partridge toggle quoted message Show quoted text -----Original Message----- From: TekScopes@... [mailto:TekScopes@...] On Behalf Of David Sent: 24 October 2012 05:18 To: TekScopes@... Subject: Re: [TekScopes] Re: line voltage 7704a Compared to the 2N6308, the 2N6307 Vcbo is 600 instead of 700 volts and the Vce is 300 instead of 350 but I suspect it will still work. Alternatively Mouser has the 2N6545 for $4.14 and the BUX48A for $4.53.
Albert #82407 Hi David, I don't understand the exact purpose of R3034. It might force an Over-Voltage Stop when R3049 gets open, but I think it's not intended to make the protection circuit sensible to the line voltage. CR3057 supplies the necessary current to keep C3049 charged (to about 100 V) to compensate the discharge current via R3049. The much smaller current via R3034 simply reduces the current via CR3057 by the same amount. (The time constants are very large compared to the inverter cycle). What will happen at increased line voltage is a slight increase in T3101 primary peak voltage, mainly because the reduced conduction periods give rise to a larger superimposed ripple. If the zener voltage is somewhat lower than designed this might trigger the Stop circuit indeed. I didn't suspect this in the first place since a too small inverter load seemed more obvious to me. Albert toggle quoted message Show quoted text --- In TekScopes@..., David <davidwhess@...> wrote: I was thinking that the Over-Voltage Stop circuit built around Q3052 is triggering at a lower primary voltage than it should be or the R3034/R3049 ratio is off. I notice that Tektronix fiddled with the network that drives Q3052 in later oscilloscope models. I suppose one could temporarily disable that circuit by removing VR3059 but I would replace it with a higher voltage zener instead. If R3034 was low or R3049 was high, that could cause the problem. VR3059 and Q3052 can cause troubles, but how would you explain that a failure there causes the inverter to stop (fall back in tick mode) when the line voltage is increased from too low to normal? Albert
Albert #82410 Hi Jerry, You know that the early 7704As had a 110 V zener? So it's not necessarily a mistake or so. For some reason (reported problems?) the later 'scopes have a 120 V zener. The total load of 10 W and so on seems more than adequate. However... I don't understand your resistor data. For instance, +5 V loaded with 15 Ohm would be (25/15 W or 1.67 W. And -15 V over 18 Ohm would be (225/18) W or 12.5 W. If the shown resistor values are what you actually used, then the total load will be much to small I'm afraid. BTW Your testload is so nicely organized that I would not dare to submit a picture of my spider web. Though cooling in mine will be better, and even then I use forced cooling. BTW a tester at the Heerenveen factory used a self-made load there for the HV lines, in case the Display unit was removed. Must be somewhere in the old messages (by me). Albert toggle quoted message Show quoted text ---- This was the unit that would run with low voltage. I later found that Cr3059(which is marked cr54 in the pix) was a 1n986, a 110V zener, which was likely causing the early shutdown. I am ordering 200 120v zeners if someone wants one or two. There are probably more 110v zeners lurking about. --- My minimum load was constructed with the following values taken from Hakan's recipe for a 7904 min-load. -50v 620?? 10W +5v 15ohm 5W -15v 18ohm 22W +50v 220ohm 15W +15v 15ohm 30W lites 15ohm 15W I think it is okay but I have no load on the HV drives. --- Jerry Massengale
Albert #82411 (continued) Hi Jerry, I looked once more at the picture of your testload. You probably mean that the resistors are rated for 10 W and so on. But their actual power consumption is much less. I calculated a total of 46 W which is not enough. Albert
Tom Miller Member Profile All Messages By This Member #82412 开云体育 Hi Albert, ? He should probably put some load on the 20 kHz drive for the HV. Maybe 20 watts or so? ? ? ? toggle quoted message Show quoted text ----- Original Message ----- From: Albert To: TekScopes@... Sent: Wednesday, October 24, 2012 3:11 PM Subject: [TekScopes] Re: line voltage 7704a ? (continued) Hi Jerry, I looked once more at the picture of your testload. You probably mean that the resistors are rated for 10 W and so on. But their actual power consumption is much less. I calculated a total of 46 W which is not enough. Albert
Albert #82413 Hi Tom, To be honest I don't think so. If the load by HV is "moved" to the +/- 50 V regulated outputs, the main effect will be a larger voltage drop across the +/- 54 V rectifier diodes. Since +54 V is (pre)regulated, the remaining crude voltages will go somewhat higher. That has hardly any effect on power consumption since the LV regulated voltages remain the same. Also the ratio +5 V/ -17V (crude voltages used in the balance check) will hardly be affected. Albert toggle quoted message Show quoted text --- In TekScopes@..., "Tom Miller" <tmiller11147@...> wrote: Hi Albert, He should probably put some load on the 20 kHz drive for the HV. Maybe 20 watts or so?
jerry massengale Member Profile All Messages By This Member #82427 what would be a good load for a reliable startup? What would be a good load for the hv drive? Jerry Massengale toggle quoted message Show quoted text -----Original Message----- From: Albert To: TekScopes Sent: Wed, Oct 24, 2012 7:34 pm Subject: [TekScopes] Re: line voltage 7704a ? (continued) Hi Jerry, I looked once more at the picture of your testload. You probably mean that the resistors are rated for 10 W and so on. But their actual power consumption is much less. I calculated a total of 46 W which is not enough. Albert
David Hess Member Profile All Messages By This Member #82428 I noticed that in the parts list. The earlier 110 Volt zener diode was a -05 which is not listed in my Tektronix parts reference so my guess is they were selecting the 110V zener diodes for ones at the high end of their voltage range. On Wed, 24 Oct 2012 18:55:16 -0000, "Albert" <aodiversen@...> wrote: Hi Jerry, You know that the early 7704As had a 110 V zener? So it's not necessarily a mistake or so. For some reason (reported problems?) the later 'scopes have a 120 V zener. . . . Albert
David Hess Member Profile All Messages By This Member #82429 I agree it is not for detecting the input line voltage but if R3034 is low enough it will have that effect. The theory section says that R3034 biases the shutdown circuit so that the startup circuit around CR3040 will work. Otherwise apparently the load of R3049 will prevent starting. On Wed, 24 Oct 2012 18:07:17 -0000, "Albert" <aodiversen@...> wrote: Hi David, I don't understand the exact purpose of R3034. It might force an Over-Voltage Stop when R3049 gets open, but I think it's not intended to make the protection circuit sensible to the line voltage. CR3057 supplies the necessary current to keep C3049 charged (to about 100 V) to compensate the discharge current via R3049. The much smaller current via R3034 simply reduces the current via CR3057 by the same amount. (The time constants are very large compared to the inverter cycle). What will happen at increased line voltage is a slight increase in T3101 primary peak voltage, mainly because the reduced conduction periods give rise to a larger superimposed ripple. If the zener voltage is somewhat lower than designed this might trigger the Stop circuit indeed. I didn't suspect this in the first place since a too small inverter load seemed more obvious to me. Albert --- In TekScopes@..., David <davidwhess@...> wrote: I was thinking that the Over-Voltage Stop circuit built around Q3052 is triggering at a lower primary voltage than it should be or the R3034/R3049 ratio is off. I notice that Tektronix fiddled with the network that drives Q3052 in later oscilloscope models. I suppose one could temporarily disable that circuit by removing VR3059 but I would replace it with a higher voltage zener instead. If R3034 was low or R3049 was high, that could cause the problem. VR3059 and Q3052 can cause troubles, but how would you explain that a failure there causes the inverter to stop (fall back in tick mode) when the line voltage is increased from too low to normal? Albert

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