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Re: 7Axx scope plugin input capacitance
John Griessen
Dale wrote:
You can remove input capcitance in scope/plugin to make the input C smaller as long as you do so at the input side of the attenuators only. You may be able to knock it down by 50%. It is unlikely that your 9pf HP probe will perform well at the high end on a modified input C scope without tweaking the comp box HF components and the scope/plugin amp will be seting the upper BW limit, not your modification. Hope that helps,Yes, that helps, and yes, I had thought of the plugin limiting speed. 7A26 spec says 21 ns risetime. Are there generic amps for sale anywhere with a 6 to 9 pF input C, outputting to 50 Ohm BNC? If not I might make one. Then you could just input to a 7A29A and use its compensated attenuators to change ranges. any noise or power draw gotchas with that idea? Passive probes are simple and good when they work, so 500MHz sounds attractive enough to experiment. John Griessen |
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Re: Off topic question - Vero boards
On Thu, May 28, 2009 at 10:37 PM, Dennis Tillman <dennis@...> wrote:
Another company selling the idential stuff is Vector ElectronicActually, this is not quite correct. The original poster was asking about stripboard, which has continous copper strips connecting the holes. To build circuits, the strips are cut with a special pad cutter tool (or the home-made equivalent). This product was very popular in England, but never caught on in the US. Vector doesn't sell it now, and I don't think they ever did. Maybe it was patented by Vero. In the US, it was common to find "pad per hole" boards, where the pad around each hole is isolated. No cutting is required, but the pads need to be jumpered together with solder blobs or soldered down component leads. This is what Vector is known for. Anyway, here's a mail order source for small stripboards (this page also shows the difference between stripboard and pad per hole board): |
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Re: 7Axx scope plugin input capacitance
Dale
--- In TekScopes@..., "hankc918" <hankc918@...> wrote:
The scope BW is tested with a 50 ohm source and 50 ohm cable, that's a 25 ohm equivalent source impedance. So 20pF and 25 ohms is a common upper testable BW at the BNC, the scope or plugin may have a lower overall BW. 9pf and 25 ohms is a much higher testable BW for a 1 meg input. Higher BW 1meg input scopes/plugins have the lower input C. Most scope inputs have a bulk adjustable capacitance at the input to adjust to a standard 20pf input spec for example. Some at 15pf, some 47pf. One trade off is that a higher input C requires a shorter probe cable and a lower input C could support a longer probe cable for 10x probes having the same probe tip capacitance for example. Most 10x probes use a fixed and adjustable shunt C in the comp box at the BNC end to achieve the LF probe comp flatness. A lower input C also enabled more control over peaking in the probe comp box for the mid and HF probe performance. You can remove input capcitance in scope/plugin to make the input C smaller as long as you do so at the input side of the attenuators only. You may be able to knock it down by 50%. It is unlikely that your 9pf HP probe will perform well at the high end on a modified input C scope without tweaking the comp box HF components and the scope/plugin amp will be seting the upper BW limit, not your modification. Hope that helps, Dale |
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Re: Major differences between TDS540 and TDS 540A aquisition board known?
--- In TekScopes@..., "Jorgen Lund-Nielsen" <dj0ud@...> wrote:
Although they initially have different P/N's they are functionally the same and in fact later they were both replaced by the same P/N (672-1408-03). I believe one difference might be a different type of RAM chips. On the other hand they also share the display module so isn't it a better idea to move your good CRT and driver board to the TDS540A ? /H?kan |
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Re: 222 power supply
Goran Roglic
Hi,
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That is correct. Two red wires are connected together. I modified all my 222,222a, 222ps and 224 (cca 6 scopes): - used 7x 2700mAh NiMh cells, - put thermal switch in serial - put external connector at rear of 222 for external charger - connect it directly to Red wire pins ( pins left and right are for +Vcc) in the middle is GND. You can use one of the pins for +Vcc. - manage ext connector not to interrupt DC voltage for scope during charging ( You will lose setup ), I use standard industrial charger for NiMh with auto trickling charge after full charge, - that work perfect, I have about 4 hours of battery life. - If battery is not empty to the end, You can use on that way, scope during charging. Charger is with floating supply. All scopes works perfect. Also I have one scope with Sanyo 2.500 NiMh, "Eneloop", very good because of small selfdischarge current. I have one adapter to BNC connector for 222, and that is very useful. Goran ----- Original Message -----
From: "Stefan Trethan" <stefan_trethan@...> To: <TekScopes@...> Sent: Thursday, May 28, 2009 6:27 PM Subject: Re: [TekScopes] Re: 222 power supply I think someone wrote a while ago that the three pin plug is to avoidit. signature database 4115 (20090529) __________
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Major differences between TDS540 and TDS 540A aquisition board known?
Hi group,
i have harvested a TDS540 which shows aquisition board error during self test. I could get a TDS540A for low quote with a smashed CRT and i think about to swap the aqui-board if possible. Are there major differences between the non-A and -A version?I wouldn't buy the 540A as a "cat in the bag" if it's unusable for my idea.. Jorgen |
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Re: R7844 focus problem update
2009/5/29 theoldtrout <angela@...>:
Good job your cat didn't walk over your open PSU as the smell of burning fur is quite horrible :-) Anyway, measured the PSU voltages and all except the 130V are high by about -- Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW A man with one clock knows what time it is; A man with two clocks is never quite sure. |
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R7844 focus problem update
theoldtrout
Sorry about the repeat of my original post below. I was trying to write an update and one of my cats walked over my PC keyboard.
Anyway, measured the PSU voltages and all except the 130V are high by about 10%. I did a swap of stuff with another newsgroup member and now have an R7844 mainframe as a spare. Changed the PSU and everything is OK. I'll repair the damaged PSU when time permits and post back results. Thanks for the help. |
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Re: Off topic question - Vero boards
Hi Michael,
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Another company selling the idential stuff is Vector Electronic ()s. It is quite commonly available here in the US from at least these three parts distrubutors: Mouser (www.mouser.com), Digikey (www.digikey.com), Jameco (www.jameco.com). Dennis -----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Michael Chang Sent: Thursday, May 28, 2009 12:33 PM To: TekScopes@... Subject: [TekScopes] Off topic question - Vero boards Dear group, Please pardon an off topic question; it's the only place I can think of asking since many of you are designers and may have worked with this. I've been searching for Vero boards for prototyping without success. Are they no longer available? I believe they are also known as strip boards - Prototype circuit boards with 0.1" center holes in grids, with each horizontal strip connected in a copper trace. Any information on sources and availability will be gratefully received. Michael |
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Re: What's the rubber pad under the 2465?
¿ªÔÆÌåÓýIt is there to protect the ICs on the main board from being crushed if you hit the bottom of the case (like when you slide it off a bench).? The seam of the case extended too far into the interior if it was hit just right.? The pad distributes the force so the case is less likely to bend. ? I remember going around to my customers and installing many of them. ? Sincerely, ? Dave WA4OBJ ? |
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Re: SC504 Trace Sudden Death
¿ªÔÆÌåÓýSorry for the long post ¨C detailed troubleshooting info follows: ? Here is the latest in my attempts to repair the HV section in my SC-504 Scope. The circuit is drawing excess current from the 25V/33.5V DC line and blowing its specified 300 mA fuse in about 5-10 seconds. A later test shows that the supply is drawing 1 Amp and not making the required voltages. ? I ended up making a 6-wire ¡°extension cable¡± to allow me to plug the back panel of the scope into the guts of a TM 515 power supply and still connect to the rest of the scope. I used my regular 500 series extender cable to power the second connector of the scope on the bench.? I can now turn the scope every which way to poke and probe. The +20, -20, +5, -5, -15V supplies are all perfect. +70Volt supply comes from the HV supply and is not happening ¨C +8 Volts at that location, and of course, no CRT accelerating voltage to speak of. ? I have tested Q1378, Q1380, Q1381 out of circuit and they test fine. I have removed the CRT, which will lighten the load on the HV transformer T1475 caused by the filament load. I have temporarily disconnected U1590, the Voltage Tripler module, no change in loading, so I hooked it back up. I have removed the Horizontal board which uses +70V from the HV supply, so that load is gone. (no change). I have tested every cap I can reach and every diode that I can get probes on ¨C no shorts or other problems found. I removed the IC U1270 and replaced it with a machined-pin socket.? A different opamp installed gives the same result. ? The 300 mA fuse and the excessive loading occurs only when the standby switch is turned on, and the +20V rail is present. I replaced the 300mA fuse with 500 mA and the fuse holds, but the two power transistors, Q1378 and Q1380 get flaming hot within 5-10 seconds. I am testing, therefore in short spurts, 5-10 seconds at a time, by connecting up my probes and then switching the unit on with the standby switch for a couple of seconds at a time. To determine the actual current draw, I substituted a lab supply with current metering to supply 25 or 33.5 Volts to the HV circuit thru the ? amp slow blow fuse, bypassing the 33.5V supply from the TM515 power module, and the current being drawn by the circuit is about 1 Amp exactly.? No wonder Q1380 and Q1381 get so toasty so quickly.? The 1 amp is drawn regardless of whether the voltage is 25 or 33.5 Volts. ? Measuring across the 1uF/160V axial electrolytic during power up results in only 8 Volts instead of 75 Volts. Power supply is squealing when it starts ¨C less so when running. ? Waveforms at collectors of Q1380 and Q1381 show that the unit is switching at something like a 8 uS rate, about 125 kHz, which I believe is much faster than usual for a properly working supply.? I am beginning to think that the problem may be in the HV transformer, T1475. ? T1475 in my unit is made by MultiComp, Inc. P/N 120-1016-00? Date code = 9218 Its winding resistances are: ? 1,2 = +/-70 Volt secondary = 1.0 Ohm 3,6 = Feedback winding = 40 mOhms 2,4 = Primary winding = 180 mOhm 7-10 = Lower third of HV winding = 11 Ohms 10-9 = Middle third of HV winding = 121.6 Ohms 9-8 = Top third of HV winding? = 126 Ohms ? I am beginning to think that the HV transformer may have an internal shorted turn or something, since it draws excess current even when mostly unloaded.? ? I did measure a discrepancy on CR1610? a 5KV, 25 mA, 250 nS rectifier diode.? According to the data sheet the max Vf is 14 Volts and at 25 mA and 25C the Vf should be about 75 to 80% of the rated Vf . which is 11.2 volts.?? My HV rectifier diode has a Vf of 6.6V at 25C and 25 mA.? I know this diode is made of multiple stacked junctions, and perhaps some of them have shorted.? Perhaps the diode is breaking down.?? I located some of them today and have a couple of new ones on the way? -- I will measure the Vf of the new ones when they arrive, which should tell me if there is a problem with the diode. ? At this point, I am thinking I should find a replacement HV transformer to try. ? Any thoughts or insights would be gratefully received. ? Steve_._,_.___ |
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R7844 focus problem update
theoldtrout
Just an update on this. I checked the PSU voltages at the test points and all, except the 130V line, are high by about 10% which is pre-regulator voltage. I did a swap of equipment with another member of this group and obtained a R7844 as a spare, so did a quick swap of power supplies and everything is now OK bar calibration. I'll repair the damaged PSU at a later date when time permits and post a report on here.
Thanks for the replies. |
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R7844 focus problem update
theoldtrout
Just an update on this. I checked the PSU voltages at the test points and all, except the 130V line, are high by about 10% which is pre-regulator voltage. I did a swap of equipment with another member of this group and obtained a R7844 as a spare, so did a quick swap of power supplies and everything is now OK bar calibration. I'll repair the damaged PSU at a later date when time permits and post a report on here.
Thanks for the replies. |
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Re: 222 power supply
Both red wires are connected to the positive battery terminal. It allows the battery connector to be mated either way roubnd and still work without letting the smoke out !!
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John Barnes ---------- Original Message ----------------------------------
From: "Randall" <N0UTJ@...> Reply-To: TekScopes@... Date: Thu, 28 May 2009 11:05:53 -0500
________________________________________________________________ Sent via the WebMail system at aztec-net.com |
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Re: Off topic question - Vero boards
Michael Chang
Thank you kindly, Geoff and John.
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I feel rather stupid now. Clearly haven't been using the right search terms. :-) Michael At 03:38 PM 5/28/2009, you wrote:
Ahem |
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Re: Off topic question - Vero boards
--- On Thu, 5/28/09, Michael Chang wrote:
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Re: Off topic question - Vero boards
Ahem
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Google is your friend, as long as you turn off cookies and cut and paste a link...... Geoff. Michael Chang wrote: Dear group, |
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zenith5106
Michael Dunn