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OT:Monitor Hantarex MT4000 12" from freq 18,4KHz to freq 15625KHz?

E

enrico

Experienced Member
Joined
Nov 4, 2007
Messages
121
Location
Pisa - Italy
Enrico, this looks similar to an Olivetti M24 monitor. I believe that those are 18KHz units--and made by Hantarex.

You might be able to get the horizontal frequency down to 15Khz, but the flyback transformer and yoke weren't made for that application. You might discover that you have an image that cannot be sized correctly, or worse, a situation that would cause the flyback transformer to fail.
 
Well with the same value of C= 4n7 and added 2Kohm to the R so it became 12,058ohm, the outpup on pin 2 is like a square wave with period of 65microsec.
So it seems that the TDA2593 works fine. So your words "but the flyback transformer and yoke weren't made for that application" made me to think that i will never use this monitor to repair my old computer... But just to understand what really happend? I never played at this game.

Enrico
 
Well, if you're willing to take the risk, you can lower the horizontal frequency by inserting an appropriate resistance in a leg of RV105 (H FREQ). The schematic says that this is a 100Kohm pot and you need to lower the frequency by about 3 KHz, or raise the value of RV105 by 3/18, which would give a resistance of about 17Kohm. I would try a standard value, such as 16K or 18K. Insert between the low end of RV105 and ground, such that RV105 is now 116K or 118K ohm. You might even be able to get the right frequency by simply adjusting RV105 without adding resistance.

That should bring the oscillator pretty close. As to the other issues of sync polarity and adjustments for linearity and image size, I'll assume that you know which controls to manage.
 
Thank you for your valuable suggestions. I tried in the follow two ways: increase the value of R146 raising it from 10k to 12k. Using the potentiometer RV105 I can not stop the lines that run and on pin 2 of the TDA2593 can see vary the period of the square wave from 75micro sec to 65microsec. The other way was to not change the value of R146 and instead inserting between the pot RV105 and the ground a res 17400ohm I can see still vary the period as above, but in any case the lines in the video represent nothing. Both sync are 3V peaktopeak, while signal seems impossible to extend over 2v peaktopeak. Let me just to know: a time on which I could make the TDA2593 working fine on 15625Hz, how the rest of power transistor and coils would works. Will they work fine or maybe they could be adjusted ONLY for to work at 18400Hz??
 
Enrico, it would be very helpful if you could provide schematics for your Model T and its monitor. There are several considerations, such as sync polarity, amplitude, etc. that might have bearing on this matter.
 
Well, the General Processo T model has been created like Steeve Jobs in a garage... There are not any kind of schematics. This my project is to assemble all possible info on it to create a resource on internet that at this moment simply NOT exists. The 2 computer i found have their analogue parte and monitor really full of rust. At this moment i'm in the process to check EACH TTL IC, EACH little board to make almost the electronic parts working fine. This is a part of my project and it is going fine. To can use 3 brand new 12" monitor i bought all togheter just for 40usd i'd like to understand to adjust them. To make them working fine at standard pal frequency i'm using the output separate signals coming out my Ferguson bigboard 1. So with it i can change polarity of h, v and video signals to be compatible with the MT4000. Here you can see how is the output video from bigboard 1 http://bitsavers.informatik.uni-stuttgart.de/pdf/ferguson/Big_Board_1980.pdf : TTL output. When i connected the outpus video to the monitor the ttl level gone down so i pulled up them with a 680ohm resistor for each signals to the +5vdc. But videosignal remain to the 2-2,5V peacktopeack. I hope those info can help.
Enrico
 
With reference to page 30 of the documentation Ferguson Bigboard I (http://bitsavers.informatik.uni-stuttgart.de/pdf/ferguson/Big_Board_1980.pdf) I'm using:


- In the case of composite output: J6-10 for the video signal and J6-9 for the ground


- In the case of separate sync output: J6-2, J6-4 and J6-6 respectively for video signal, Hsync and Vsync.


In each case, I proceeded to set the jumpers on JB1 according to the needs of the monitor I'm using. In the case of MT4000 Monitor Hantarex I made JB1-1 with JB1-12, JB1-8 with JB1-9 and JB1-10 with JB1-11 and checked with oscilloscope that the output signals are all positive as required from the entrance monitor.
 
MORE NEWS, but i need help YET.

I'm still working and thankfully everything seems possible.
I state that I bought 3 CRT monitors for only 30 € total a couple of years ago.
The piece with which I was doing the tests at the end made me lose time, in fact:
I got an old IBM PC 5150 that I have and that has a monochrome MDA output with 18KHz horizontal sync
I created a little circuit with a 74LS86 chip in order to reverse the vertical sync cause the CRT want 3 separate signals but all with a positive pulse
the first CRT monitor has not wanted to know to be adjusted to see anything.
I took the second, and finally I was able to see the video played by the ibm pc with its Hsync at 18KHz.
Then I took another my old computer that is Ferguson Bigboard I. It video PAL 15KHz outputs can be modified with its jumpers to have composite or separate outputs and all with the polarity manageable via jumpers.
Configured all its outputs with positive polarity i reinforced them with pull-up resistors, then I connected them to the CRT monitor.
I then began to make the following modifications:
1) change the value of the res R146 (12Kohm) to allow the TDA2593 to extract the frequency of 15625Hz
2) change R145 to be able to catch the horizontal frequency of the pot with RV105
3) change R127 to be able to adjust the vertical frequency with the RV106 following the TDA1170N product description
For now, the video can be seen but it seems replicated and slowly swifts as the following video:
https://www.dropbox.com/s/9o28jkil3v1ly0c/Video che scrolla MKV.mkv?dl=0
The schematic of the crt monitor is instead at this link:
https://www.dropbox.com/s/h2qzl64v4jv2ygf/Hantarex MT4000.pdf?dl=0
Thank you for any further help ....

Enrico - Pisa
 
[SOLVED]

Thanks to the helpful suggestions of Paul from it.comp.retrocomputing have succeeded in the goal to modify my 3 MDA Hantarex MT4000 12" green phosphor monitors working at the frequency of 18.432Hz to make them work at 15.625Hz (PAL standard frequency in europe) and therefore possibly use them as soon as I completed to repair General Processor Model T that I have on the workbench.


Below modified i done.


1) changing res R146 from 10Kohm to 12Kohm: in this way, the TDA2593 can do so do manage to pot RV105 adjustment of the horizontal frequency.
2) Changes the value of R120 from 1mohm to the value of 120kohm and C112 from the value of 68nF to values ​​between 100nF and 200nF. Lowering the value
will raise the level of the pulse signal input and the vertical larger capacity allows you to hold it for more time so that can be managed by TDA1170N.
3) Change the value to the value of R132 from 390kohm to 330kohm so able to easily change the width of the vertical picture
4) Change the value to the value of R127 from 180kohm to 133kohm (putting a res from 470kohm in parallel) in order to better manage the hooking the vertical blanking
5) Changing the value of R145 from 82kohm to the value of 23kohm so that the pot RV103 can adjust the frequency to the vertical center of its excursion.


Other things to do. ... as soon as possible.


a) Adjust the horizontal width of the picture
b) Adjustment of the advance of the horizontal lines in order to
If necessary, move the picture to the left more.


I honestly did not expect to be able to succeed and above all to receive a help is so important and some from the list and particularly by Paul.


The picture clears up any doubt.
https://www.dropbox.com/s/c9ld8uvicwwfef0/MT4000 funzionante 20140928_225010.jpg?dl=0

Sorry for my english (Google translator helped me.. so i made some little adjusts)

Enrico - Pisa (ITALY)
 
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