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M1212 Monitor flyback transformer

M

mmx01

6502
Hi All,

Anyone knows where to buy a replacement for EHT for this monitor? There's no high voltage output (screen is not highlighted) and upon inspection EHT has white residue on it. Probably cracked/epoxy leaked somehow.

Checked caps all are good, Measured HOT transistor, transformer seems also good. Nothing is burnt on the PCB itself or damaged in other way.

EHT is either Sony 1-453-133-11 or MTI 154-0139. Cannot find them on-line anywhere closest was 1-453-187-11 but does not look identical. Are they compatible?

Regards

Mariusz

 
If the flyback is "shorted" bad, it takes the HOT with it nearly every time. 

If the HOT is ok, then its equal chances of being a flyback or something else. Especially if you get a spirt of high voltage, and then shutdown. 

 
Last edited by a moderator:
Hard to tell if EHT is shorted with just regular multimeter. Any way to check for EHT startup safely?

Checked HOT transistor and it is good no short and tested after de-soldering.

When I turn the monitor on I hear de-gaussing loop working  but no image, not even background (white) despite playing with brightness and contrast.

When I disconnected HV cap also no "HV click" to a discharge probe. Perhaps in circuit measurement of B+ presence and other 84/100V voltages would help to narrow possible issue? M1212 is not the same board layout as the other one with leaking caps. I recapped it but nothing has leaked/no damage.

 
You need to measure the HV coming in to see if you get a burst during first startup. 

If not, We can safely rule out the flyback and potentially you are missing your horizontal drive signal for some reason, whether its B+ related or whatnot. 

I don't think those monitors come on without a reference signal coming from the video card though, but I could be wrong. So until you have a proper working Mac with a clean video signal, you cant really begin to troubleshoot anything. 

 
Yup, was thinking about that too, assumed such level of sophistication was not present but that may be wrong.  Found old schematics so soldered in EHT back and measured voltages. Can't find any datasheet about LSC1178B but it gets RGB/sync signals in and outputs RGB + drives HOT so it may well be.

PS output TP1 should be 84V is 110V, TP2 should be 17V is 20V, TP3 should be 8.4V is 10V. One reason I could think of is that it is running without load since this is after transformer so nothing to pump voltages up on all rails.

 
Its going to measure high if there is no load on the power supply. 

I havent found the schematics to these monitors. Where did you get them by chance? 

 
That doesnt surprise me considering CRTs arnt made anymore, and they are CRT Specific chips. 

looks like the Jungle IC/Scan processor is a proprietary one. So hopefully restoring a signal to this monitor fixes it, otherwise if that IC is bad? Game over. 

 
This one worked out well. Replaced 99% of caps and re-soldered wires going to the base and the image is on. It will not power on without source attached though. On the board the main IC is a proprietary one but also other parts/drivers are long obsolete. Best path is to get a similar/same board as a donor. EHT still has got "wining" sound even though I soldered centre rod under pressure but image is acceptable.

 
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