Sooo,
I am trying to get a ctm-644 going again.And I am wondering if anyone that has repaired one would have any specific areas that I should look in?
I have looked at the schematics and service manual,but I know often there can be a common fault component.I do have a working ctm-644 for comparison.
It is still outputting 5v and 12v fine,these are stable with no issues.
The screen is completely blank,nothing,no change in it at all when powered on.No static from the glass,not even a flicker.It doesn't make that sound that you get when a crt powers up.
I put my multimeter on the pins of the din connector of both monitors and noted that there was low voltages on the pins of the working monitor but none on the faulty one.
Im thinking its the flyback or flyback caps,(do flybacks go?).I know i need to be careful with this high voltage circuit and will need to discharge the tube before working on it.I have gotten a lend of an esr meter and i am wondering would the esr of the flyback caps tell me anything?This esr meter can measure esr in series but not capacitance,would desoldering them and testing them be a good place to start?
Any ideas are most appreciated!
If the screen isn't giving the normal static tingle when it's on, then the HT transformer is dead (yes, they do die). It could be a broken joint, but unlikely. Unfortunately fixing this is unlikely to be financially viable.
Bryce.
Ah,
Thats a pity.
Any idea how I could check the ht transformer Bryce?Preferably while I have it discharged!!
The transformer would be specific to the monitor i suppose.I was thinking of getting an old 14"crt tv and harvesting one from that.
Thanks a million for the reply Bryce.I managed to get that c16 going again,it was the cpu,i didnt find that out until after i had replaced the ram :doh: .A friend of mine gave me the cpu out of his plus 4 to try in it and away it went.Those cpu's sure are pricey!
Your problem with the 644 sounds exactly like what has happened to my 640. There is no static or sound at all.
Quote from: magentis on 12:52, 07 April 16
Ah,
Thats a pity.
Any idea how I could check the ht transformer Bryce?Preferably while I have it discharged!!
The transformer would be specific to the monitor i suppose.I was thinking of getting an old 14"crt tv and harvesting one from that.
Thanks a million for the reply Bryce.I managed to get that c16 going again,it was the cpu,i didnt find that out until after i had replaced the ram :doh: .A friend of mine gave me the cpu out of his plus 4 to try in it and away it went.Those cpu's sure are pricey!
Unfortunately these are monitor specific. The transformer from any random CRT will not fit. The quickest, easiest and safest test is to put the back of your hand near the screen glass. If the hairs on your hand don't feel the static, then you are most likely out of luck. There are a few passives that would also cause this, but it's unlikely and they can also only be properly tested when they are powered (with high voltages).
Bryce.
From an economical stand point, It is cheaper to find an other CTM than trying to buy a new THT (rare & expensive), especially since you will have to change some capacitors as well...
Thanks very much guys for the help.
CRTs are like oil now, even if it's not economically relevant to repair them yet, it will be as they become more and more rare.
There will probably be a small niche, like with many other things... however I guess that they will tend to disappear sooner than later, partially because they are dangerous to repair and partially because they are picky and far from practical: image quality can change just moving them from here to there, convergence is not consistent in the edges of the screen, they exhibit certain degree of vignetting... for instance, I have a big speaker close to mine and I need to degauss it every week with a coil :) I mean, I enjoy it because it reminds me when I was 8 and looks better than my previous approach, but to be honest I am itching to find an alternative solution without too many compromises in the future, although this still seems difficult in 2016. I am thinking to try the Framemeister in the mid future but apparently it is not perfect either...
Quote from: Bryce on 12:37, 07 April 16
If the screen isn't giving the normal static tingle when it's on, then the HT transformer is dead (yes, they do die). It could be a broken joint, but unlikely. Unfortunately fixing this is unlikely to be financially viable.
Bryce.
Sad to know it happens.
Just wondered if a Transformer will simply fail over time, or if a power surge or drop in electricity will cause a Transformer to fail?
Quote from: AMSDOS on 00:15, 09 April 16Just wondered if a Transformer will simply fail over time, or if a power surge or drop in electricity will cause a Transformer to fail?
It very much depends on the transformer and the application.
Normal mains transformers are one of the most reliable electric/electronic devices there is. But high voltage, high frequency transformers like Line OutPut Transformers (LOPT) are far less reliable. Most LOPT are not run from the mains directly, but from a high voltage DC rail that is smoothed, so a fast mains transcendent (surge) is not likely to cause problems, as the smoothing capacitor for the DC rail will absorb it. However, repeated surges may cause damage. A drop in the mains voltage (as long as it is not too much, and for not too long) will have little effect. If it drops too low, the system may malfunction, or a protection circuit may be activated (causing shut down) but it is unlikely that damage will result.
There is though, the stress in any high voltage system caused when you switch it on. Plus the insulation in these high voltage transformers has to be perfect. If the insulation degrades even a little, the high voltage will find a way to leak through it. As soon as even a small current flows, it will flash-over and a high current conductive path is then formed - the LOPT is then toast.
There is also a possibility that the electronics that drive the LOPT have died. That was a very common fault in domestic TVs at one time. But since then, the quality of the high voltage switching transistors improved and the faults became less common.
Mark
All good info accept for one small detail. ALL transformers are driven with AC, not DC. Even LOPTs. If you put DC into a transformer nothing would come out the other end :)
Bryce.
Gesendet von meinem Motorola DynaTEC 8000X mit Tapatalk 2.
Quote from: Bryce on 11:29, 09 April 16
If you put DC into a transformer nothing would come out the other end :)
Bryce.
Gesendet von meinem Motorola DynaTEC 8000X mit Tapatalk 2.
Errr Perhaps Smoke. :laugh:
Ray
Quote from: 1024MAK on 11:21, 09 April 16
It very much depends on the transformer and the application.
Normal mains transformers are one of the most reliable electric/electronic devices there is. But high voltage, high frequency transformers like Line OutPut Transformers (LOPT) are far less reliable. Most LOPT are not run from the mains directly, but from a high voltage DC rail that is smoothed, so a fast mains transcendent (surge) is not likely to cause problems, as the smoothing capacitor for the DC rail will absorb it. However, repeated surges may cause damage. A drop in the mains voltage (as long as it is not too much, and for not too long) will have little effect. If it drops too low, the system may malfunction, or a protection circuit may be activated (causing shut down) but it is unlikely that damage will result.
There is though, the stress in any high voltage system caused when you switch it on. Plus the insulation in these high voltage transformers has to be perfect. If the insulation degrades even a little, the high voltage will find a way to leak through it. As soon as even a small current flows, it will flash-over and a high current conductive path is then formed - the LOPT is then toast.
There is also a possibility that the electronics that drive the LOPT have died. That was a very common fault in domestic TVs at one time. But since then, the quality of the high voltage switching transistors improved and the faults became less common.
Mark
Thanks for that. Was merely wondering about the Transformer inside the Amstrad Monitors, @Bryce (http://www.cpcwiki.eu/forum/index.php?action=profile;u=225) mentions HT Transformer, which I presume is seperate from a LOPT, though Google Images displays the Large Transformers you get around Power Substations.
Of course I may just have to accept that every electronic component will eventually fail.
Quote from: AMSDOS on 22:57, 09 April 16
Thanks for that. Was merely wondering about the Transformer inside the Amstrad Monitors, @Bryce (http://www.cpcwiki.eu/forum/index.php?action=profile;u=225) mentions HT Transformer, which I presume is seperate from a LOPT, though Google Images displays the Large Transformers you get around Power Substations.
Of course I may just have to accept that every electronic component will eventually fail.
HT stands for High Tension (meaning high voltage), in the UK, I was taught that the LOPT is used get the EHT (Extra High Tension = extra high voltage) required for the CRT (Cathode Ray Tube) as well as driving the horizontal coil (so each line is scanned across the screen). So we are both taking about the same thing, just using slightly different terminology. All CRT displays use a LOPT. In "simple" designs, the LOPT is the only transformer in them (the more complex TVs have extra features and so may have extra transformers). CRT monitors are relatives of CRT TVs. Monitors lack TV tuners. So for the CTM-644, it is the LOPT that we are talking about.
Also, a clarification. Bryce is correct, all transformers only work with AC waveforms. However, LOPT are driven by a pulse waveform from a transistor acting as a switch. The supply used for this is a DC supply. So the DC is chopped up (by the transistor) and therefore becomes a AC waveform. I hope that helps explain things ;-)
More info on LOPT here (https://en.wikipedia.org/wiki/Flyback_transformer). HT and EHT (https://en.wikipedia.org/wiki/HT_%28vacuum_tube%29). Plus lots more if you research CRT TV technology.
(http://i00.i.aliimg.com/img/pb/430/091/608/608091430_148.JPG)(http://www.desmoines-classifieds.com/Downtown-/Household-Goods-/Repair-Parts-/Marconi-2955-flyback-lopt-replacement-kit-adimage.jpg)(http://www.electronicrepairguide.com/images/flyback%20transformer%20internal.jpg)
Mark
I seem to recall noticing something like that, when I took my monitor to the TV Repair man last year, because I think he said that was the only component that he couldn't repair, which sat on the back of the board I think & had that lead running to the back of the Tube.
Quote from: AMSDOS on 22:57, 09 April 16
Thanks for that. Was merely wondering about the Transformer inside the Amstrad Monitors, @Bryce (http://www.cpcwiki.eu/forum/index.php?action=profile;u=225) mentions HT Transformer, which I presume is seperate from a LOPT, though Google Images displays the Large Transformers you get around Power Substations.
Of course I may just have to accept that every electronic component will eventually fail.
Yes, we're both talking about the same part. HT Transformer is a generic description for and large stepup transformer. LOPT probably describes it more accurately.
Bryce.
Hi All
Over here they are referred to as " Flyback Transformers "
Ray
Quote from: Audronic on 23:58, 10 April 16
Hi All
Over here they are referred to as " Flyback Transformers "
Ray
Is that because they pulsate, that the term Flyback is used?
Flyback Transformer !
The flyback pulse is almost vertical therefore the rate of change of flux is high, therefore the output voltage is high.
I am having dificulty in explaining it. So if some body can do a better explanation Please hop in.
Thanks
Ray
Yes, they are difficult to explain. Here's my attempt:
A normal transformer usually gets fed with a sinewave signal. The primary coil (input) builds up a magnetic field relatively slowly in the core as the current rises. As the current begins to fall (falling edge of sinewave) the magnetic energy creates a current in the secondary coil (output). Sinewave in -> Signwave out.
With a Flyback transformer, a sawtooth wave (like this /|/|/| ) is used to drive the primary side. This has the effect that the sudden drop in current of the falling edge (under 1µS) causes the magnetic field to collapse and the entire energy is dumped into the secondary coil very quickly, giving a mirrored sawtooth output (Like this |\|\|\ ).
However, the name Flyback doesn't come from how it works, rather its function in the TV. The sawtooth is the 15Khz signal we all know from retro computers. The slopped edge of the output is the horizontal line scanning across the screen. The sharp rising voltage (leading edge of the ouput signal) is what make the electron beam "Fly back" very quickly to the other side of the screen.
Bryce.
And, of course, after the term was used in the TV industry, simular high frequency (compared to mains "line" frequency 50 Hz or 60 Hz) transformers used in some types of switch mode power supply units also are often called flyback transformers. Although there are various differences in the circuit design.
Mark