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Strange focus error on Oscilloscope Hameg HM1005
Hi,
I'm currently having trouble with my good-ol' HM1005. It has some problems focusing correctly. When it's cold, you first see nothing on the screen. Increasing intensity results in an almost completely glowing screen, looking like an EL-backlight. Leaving it on for some minutes shrinks the glow more and more to a spot (in X/Y mode) or to a horizontal line (in normal operating mode). Now it's possible to use that thing, but it's not completely working correct. On the left side of the line the beam is more intense. I've made a photo of that, please have a look at http://www.preamp.org/dinge/hm1005.jpg. Using a time base of 50ns shows some kind of overshoot next to that bright spot. The trace is moveable to X and Y as it should (I did that on the photo, so the bright spot is not on the grid). I'd appreciate any kind of help that can lead me to the source of this strange behaviour. Thanks in advance and with best regards from Germany, Lasse |
Strange focus error on Oscilloscope Hameg HM1005
wrote in message
... Hi, I'm currently having trouble with my good-ol' HM1005. It has some problems focusing correctly. When it's cold, you first see nothing on the screen. Increasing intensity results in an almost completely glowing screen, looking like an EL-backlight. Leaving it on for some minutes shrinks the glow more and more to a spot (in X/Y mode) or to a horizontal line (in normal operating mode). Now it's possible to use that thing, but it's not completely working correct. On the left side of the line the beam is more intense. I've made a photo of that, please have a look at http://www.preamp.org/dinge/hm1005.jpg. Using a time base of 50ns shows some kind of overshoot next to that bright spot. The trace is moveable to X and Y as it should (I did that on the photo, so the bright spot is not on the grid). I'd appreciate any kind of help that can lead me to the source of this strange behaviour. Thanks in advance and with best regards from Germany, Lasse Did it gradually or suddenly go wrong? If you feed in a known accurate ,say, 1V pk-pk 1KHz signal in, does it give the correct screen indication of 1V, 1KHz with relevant settings ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
Strange focus error on Oscilloscope Hameg HM1005
Did it gradually or suddenly go wrong? I'm sorry I can't answer that. I haven't used it for a couple of years... If you feed in a known accurate ,say, 1V pk-pk 1KHz signal in, does it give the correct screen indication of 1V, 1KHz with relevant settings ? I made another 2 photos. Used a HZ 154 probe on the internal CAL.- outlet. Looks weird to me... http://www.preamp.org/dinge/hm02.jpg http://www.preamp.org/dinge/hm03.jpg |
Strange focus error on Oscilloscope Hameg HM1005
wrote in message
... Did it gradually or suddenly go wrong? I'm sorry I can't answer that. I haven't used it for a couple of years... If you feed in a known accurate ,say, 1V pk-pk 1KHz signal in, does it give the correct screen indication of 1V, 1KHz with relevant settings ? I made another 2 photos. Used a HZ 154 probe on the internal CAL.- outlet. Looks weird to me... http://www.preamp.org/dinge/hm02.jpg http://www.preamp.org/dinge/hm03.jpg But does the trace agree volts and usec, X and Y, with the CAL signal? I cannot see the graticule. Is there an optoisolator/optocoupler in the CRT drive circuit? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
Strange focus error on Oscilloscope Hameg HM1005
"N_Cook" wrote in
: wrote in message . .. Hi, I'm currently having trouble with my good-ol' HM1005. It has some problems focusing correctly. When it's cold, you first see nothing on the screen. Increasing intensity results in an almost completely glowing screen, looking like an EL-backlight. Leaving it on for some minutes shrinks the glow more and more to a spot (in X/Y mode) or to a horizontal line (in normal operating mode). Now it's possible to use that thing, but it's not completely working correct. On the left side of the line the beam is more intense. I've made a photo of that, please have a look at http://www.preamp.org/dinge/hm1005.jpg. Using a time base of 50ns shows some kind of overshoot next to that bright spot. The trace is moveable to X and Y as it should (I did that on the photo, so the bright spot is not on the grid). I'd appreciate any kind of help that can lead me to the source of this strange behaviour. Thanks in advance and with best regards from Germany, Lasse Did it gradually or suddenly go wrong? If you feed in a known accurate ,say, 1V pk-pk 1KHz signal in, does it give the correct screen indication of 1V, 1KHz with relevant settings ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ First,check all the power supplies.Voltage and ripple. then determine if the sweep circuit is working,then check the unblanking waveform and Z-axis amp. you should be able to vary the amplitude of the unblanking pulse at the output of the Z-axis amp,with the brightness control.(not the CRT bias pot) -- Jim Yanik jyanik at kua.net |
Strange focus error on Oscilloscope Hameg HM1005
But does the trace agree volts and usec, X and Y, with the CAL signal?
Amplitude is correct, but neither is the frequency nor the duty-cycle. Is there an optoisolator/optocoupler in the CRT drive circuit? Couldn't find any. If you have a saw-tooth-generator, can you try that as an X- deflection source? Maybe there's one in our workshop, if so I'll try it tomorrow. This does, however, not explain the focus problem. So I'd follow Jims suggestion: First,check all the power supplies.Voltage and ripple. I'll do that tomorrow, too, as I don't have a second Oscilloscope at home. |
Strange focus error on Oscilloscope Hameg HM1005
Sounds like a good time to replace the electrolytic capacitors.
I once had an old B&K Precision oscilloscope that I bought very cheaply because it had a focusing problem. It turned out to be an open resistor. The focus volage came from the flyback transformer, went through a chain of 22-megohm resistors, and then to the picture tube. One of those resistors had opened up, causing the won't-focus-properly problem. Your 'scope may have a cold solder joint in this area. |
Strange focus error on Oscilloscope Hameg HM1005
On Sat, 10 Jan 2009 12:21:59 -0800 (PST), wrote:
Did it gradually or suddenly go wrong? I'm sorry I can't answer that. I haven't used it for a couple of years... If you feed in a known accurate ,say, 1V pk-pk 1KHz signal in, does it give the correct screen indication of 1V, 1KHz with relevant settings ? I made another 2 photos. Used a HZ 154 probe on the internal CAL.- outlet. Looks weird to me... http://www.preamp.org/dinge/hm02.jpg http://www.preamp.org/dinge/hm03.jpg Your pictures are showing the retrace (which should be blanked). The bright spot at the left is where the beam is stationary awaiting the next trigger edge (this should also be blanked). You can confirm this by free-running the timebase when the bright spot should disappear. Your problem is that either the brightness/brilliance control (front panel or internal preset) is set far too high, or the blanking waveform is missing. The first cause can also be due to incorrect high voltage supplies and the out-of-focus reported may be another effect of this. -- Geo |
Strange focus error on Oscilloscope Hameg HM1005
I have not worked on this model of scope, but I can maybe give some
suggestions. Check that the main power supply is working to specs. Then check that the high voltage and focus supply are to specs. Because you are saying that the display is sort of dim on one side compared to the other and there is soft focus, this is a possible indication of voltage regulation, and switching power supply DC filtering problems at its outputs. Some scopes that I have worked on had high voltage modules that supply the anode and focus supply. I have had the module go defective causing your described fault. The last alternative if you feel it is worth while, is to call the manufacture and see if they would service the scope. Or, see if you can find a working used one of the same model. This way, you may be able to have some spare parts. Jerry G. __ On Jan 10, 1:35*pm, wrote: Hi, I'm currently having trouble with my good-ol' HM1005. It has some problems focusing correctly. When it's cold, you first see nothing on the screen. Increasing intensity results in an almost completely glowing screen, looking like an EL-backlight. Leaving it on for some minutes shrinks the glow more and more to a spot (in X/Y mode) or to a horizontal line (in normal operating mode). Now it's possible to use that thing, but it's not completely working correct. On the left side of the line the beam is more intense. I've made a photo of that, please have a look athttp://www.preamp.org/dinge/hm1005.jpg. Using a time base of 50ns shows some kind of overshoot next to that bright spot. The trace is moveable to X and Y as it should (I did that on the photo, so the bright spot is not on the grid). I'd appreciate any kind of help that can lead me to the source of this strange behaviour. Thanks in advance and with best regards from Germany, Lasse |
Strange focus error on Oscilloscope Hameg HM1005
wrote in message
... But does the trace agree volts and usec, X and Y, with the CAL signal? Amplitude is correct, but neither is the frequency nor the duty-cycle. Is there an optoisolator/optocoupler in the CRT drive circuit? Couldn't find any. If you have a saw-tooth-generator, can you try that as an X- deflection source? Maybe there's one in our workshop, if so I'll try it tomorrow. This does, however, not explain the focus problem. So I'd follow Jims suggestion: First,check all the power supplies.Voltage and ripple. I'll do that tomorrow, too, as I don't have a second Oscilloscope at home. Cal of 1MHz ? , if the screen display geometry agrees with the CAL then unlikely a problem with the EHT/ PDA and focus problem from that from my repair briefs Hameg HM103 scope Lack of flyback suppression Replace the optoisolator -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
Strange focus error on Oscilloscope Hameg HM1005
I've made some first measurements. The power supply seems OK at first
sight, but the sawtooth doesn't look that good. I found out that when I set the trigger switch to LINE (~), the sawtooth shows only every 10th tooth, the rest of the time it's GND level. The trace looks like a bright spot on the left and a really dim line to the right. If I use the trigger level switch, the sawtooth is totally missing! In the schematic, on the timebase page, there's a signal called "PDPA". This is high while the trigger level switch is 'used'. In normal operating mode, there's a duty cycle of about 90% to 10%. This clips the sawtooth at the ground level, which could explain the bright spot on the left at the trace. What is this PDPA for and why does the trigger affect the sawtooth? The schematic is available from hameg.com, look under manuals. |
Strange focus error on Oscilloscope Hameg HM1005
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Strange focus error on Oscilloscope Hameg HM1005
On Sat, 10 Jan 2009 10:35:48 -0800 (PST), wrote:
In my opinion, seems a blanking problem Good luck |
Strange focus error on Oscilloscope Hameg HM1005
I used the german version.
http://www.hameg.com/manuals.0.html?...mdownloads_pi1[mode]=download&tx_hmdownloads_pi1[uid]=955 |
Strange focus error on Oscilloscope Hameg HM1005
Geo wrote in message
... On Mon, 12 Jan 2009 00:03:35 -0800 (PST), wrote: I found out that when I set the trigger switch to LINE (~), the sawtooth shows only every 10th tooth, the rest of the time it's GND level. The trace looks like a bright spot on the left and a really dim line to the right. Good description of the hold-off control being in the wrong position. The schematic is available from hameg.com, look under manuals. I looked but the manual I found was only 28 pages with no schematics - url? -- Geo Thanks for the heads-up I downloaded the manual for my usual low spec scope HM412-5 and the schema are in there. I've previously repaired it blind (CMOS 4011 failure of all things). -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
Strange focus error on Oscilloscope Hameg HM1005
CMOS 4011 failure of all things
There're some 7400 and 74132 in there, should I change them? I'm not sure wether there's a blanking problem, since the sawtooth is directly affected by the trigger. The hold-off regulator seems to have no effect at all. The second timebase is also affected, seems that both of them influence each other. |
Strange focus error on Oscilloscope Hameg HM1005
On Mon, 12 Jan 2009 03:02:11 -0800 (PST), wrote:
I used the german version. http://www.hameg.com/manuals.0.html?...mdownloads_pi1[mode]=download&tx_hmdownloads_pi1[uid]=955 Ok - some parts not very legible - but suggest looking at the two monitoring points MP7 and MP6 (page 44 of german manual) for the blanking waveform. Regarding the hold-off - fig 2 on page 15 of the "englisch" manual shows the effect you described. -- Geo |
Strange focus error on Oscilloscope Hameg HM1005
The problem is solved!
Unfortunately it was a very... stupid one. The coax-cable for the Z- signal was not correctly soldered to the CRT-board. I asked my father about that (I got the scope from him). He said that it was bought from eBay a while ago. I guess the previous owner messed something up in there. However, thanks to all of you for your tips and suggestions, I really appreciate that! Best regards, Lasse |
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