Makvision D3129 (or 3125 or 666 clone)

[lilshawn]

Had a monitor come in (Makvision D3129) that someone else has worked on. I switched out most of the electrolytic caps and got the B+ flowing again. a few voltages are ever so slightly low, but within a margin of error I think.

+25 @24.8
+12 @12.0
+7@6.78
+150@155

the monitor doesn't seem to switch video modes it appears to stay stuck in default 15k scan regardless of the video sent in. no video appears to be going through. if i crank up the brightness to view the raster I can see the following:

the top and bottom of the raster scan are rock solid...nice and even, but the middle of the scan jitters around and crosses over itself. I suspected the vertical deflection IC...It appears someone has had a go at replacing the vertical deflection IC  (IC and a transistor (Q 29)... I'm unsure if it's original or replaced but there is fresh solder and flux there. I double checked the diodes and resistors feeding the power in and out and all seems good. still does it.

I went ahead and replaced the vertical deflection IC and it's power resistors that feed it voltage (sometimes they get fried when the chip starts to go) still does it.

The only thing coming to mind is those stupid mystery chip boxes that weiya stick on there. (labled as IC5) it's a micro controller that reads the sync coming in and switches the scan rate from 15k to 25k to  31k. I'm just thinking it's dead and running random.

FOR FUTURE INFO:

the pinout is:

1 out to Q17
2 out to Q16
3 out to Q21
4 Vert sync
5 Horiz sync
6 +5v
7 GND



the truth table for the microcontroller is as follows:

at CGA:

Pin 1 LOW
Pin 2 HIGH
Pin 3 HIGH

at EGA


Pin 1 HIGH
Pin 2 HIGH
Pin 3 LOW

at VGA


Pin 1 HIGH
Pin 2 LOW
Pin 3 HIGH

I'm going to jump the pins high to CGA (there are pads for it on the backside of this chassis) to see if it comes around.

if so, the micro is dead. if not 

[ed12]

>
The only thing coming to mind is those stupid mystery chip boxes that weiya stick on there. (labled as IC5) it's a micro controller that reads the sync coming in and switches the scan rate from 15k to 25k to  31k. I'm just thinking it's dead and running random.
<
just to get it right
ic3 or ic5 ?

ed

[lilshawn]

it's similar to the 2929 but not quite...

[ed12]

oh
the pic chip

ed

[grantspain]

i have had loads of those ic go faulty,sometimes they just won't sync and sit there clicking other times i have similar screens to yours

[lilshawn]

this particular board has a couple solder pads adjacent to the 2 & 3 outputs for that IC box......The idea being you are to drag solder over to the trace from the pins to force the unit to 15k for testing.

I have modded the board in this fashion, but i got sidetracked this afternoon doing some other stuff so i didn't get a chance to throw the chassis back in and test it yet.

i'm hoping it works. if it does, i'll just jump the pins to force it to VGA and be done with it. it's out of a Big Buck hunter pro cabinet, so it's going to run VGA regardless.

[lilshawn]

noticed the resistor (R50) that feeds the diode from the SMPS for the 25 volt had been replaced with a 1.5 ohm resistor at some time instead of the spec'd 0.47 ohm. this was resulting in the voltage sagging down to 22.3 after I replaced the Vertical IC... pin 14 on the vertical IC was at 21.7 volts.

replaced resistor with 0.47 and it brought the voltage back up to 24.3 volts with the IC getting 23.7 at pin 14.

voltage is better but still running whacky. instead of just being gibbled in the middle the whole lower 3/4 is gibbled.


not sure where to go from here. I put in a message to Mr. Nieman and see what he thinks about this.

[DudeRegular]

I don't have any advice on this, but I have one of these monitors in my MAME cab. It looks like you are kinda stuck with not easily testable options. Let me know if you need a measurement from somewhere on the chassis. I will give it a shot. Well assuming I can get to the spot without shocking myself .

[ed12]

without going to the warehouse and testing this,
unsloder pin 1 on the pic,make sure the land is clean and the pin is free.
then fire it up and see what the vert dose.?
very short test as it is in the vert sync circuit

ed

[lilshawn]

I hotwired the board to run in 15k. I removed the PIC board entirely so it's.... completely out of the picture......


*The Who - Won't Get Fooled Again plays*

without the PIC controlling the high voltage switching it just sort of runs the vertical deflection but no B+HV is generated. so there is no horizontal deflection.

Using the logic truth table, i grounded pin1 low and tied the other pins 2 and 3 to the output of the +5v regulator for the PIC circuit... that way, when i start up it's immediately in 15k mode. I want a stable baseline for testing.

I went ahead and swapped out the 741 that does some BS for the horizontal since it runs on the same +25 as the vert IC. but no change.

[ed12]

ya thats the truth table for the pic,
the 741 as in op amp ?
ref me in the circuit plz.
and u say with the ic out the unit fully fire's up ?
as i do not understand?

>vertical deflection but no B+HV is generated. so there is no horizontal deflection<

with the ic out,u should not get any horz def.

ed

[lilshawn]

sorry not 741...

LM358 - IC10

got my opamps mixed up

with the PIC removed out of circuit, it does not fire up. because it handles the switching of the B+ for the different frequencies, when removed...the horizontal does not run because no B+

I initially thought maybe the PIC was doing something random so I removed the PIC and hotwired the chassis to run at 15k till i figure out the vert deflection issue.

so yes it's removed...but i have it hotwired to run.

[ed12]

ok..thk-u
i thought i had read the full thing wrong..even the schematic.

so then with the pic out it is locked to a freq and will work ?

ed

[grantspain]

for the vertical problem have you checked c67?

[ed12]

c67 is on pin 1 of the vert ic :sync input:...really dose not control the res's

ed

[grantspain]

sorry must have read the post wrong,i thought he had a vertical issue with part of the screen as well as a freq issue

[ed12]

ya it took a twist on me to
no foul

ed

[lilshawn]

no worries... I believe this chassis has a few different problems. I'm trying to narrow down the issues so I can work on them one at a time.

I'm just trying to get a nice even stable raster at this time. I'll work on the sync sense and auto switching after. (monitor wont switch to VGA if fed a VGA signal...i mean who knows... maybe they are related.)

I've already gone through all the caps in the vert section (including c67) and replaced all the 'lytics to be extra sure. i paid extra attention to c66 since it's got to do with the timing internal oscillator.

[ed12]

it was 5 drives ago,or i would up load the pic code for u to put this thing down..there a dog i know.
did u hear from rick ? if not i can and should chat him tommrow

ed

[lilshawn]

Not in the email I sent just recently... I did talk to him a few months ago about this monitor when I called him about getting a replacement chassis for another monitor.  He basically said to check the voltage going into the vertical deflection IC cause it sounds to him like that would cause it.

I have a feeling I may have to give up on this monitor.  It's  already cost a pile of my time to try and fix it.  If it was sitting in my garage I'd just work on it whenever but when it's on company time... It might just get the axe.

[ed12]

ok
i have some side line stuff for him,
will let u know

ed