DIY Hantarex MTC9000 Monitor Chassis Repair Manual
DO-IT-YOURSELF HANTAREX MTC9000 REPAIRS
The content of this document is the intellectual property of M.Scotford and must not reproduced in part or full, without written permission from him.
WARNING
The Hantarex Chassis like all monitor chassis, operates at very high, lethal voltages and so repairs to these monitors should only be attempted by qualified engineers who have a full understanding of working safely, with high voltages.
This instruction sheet is provided as a guide/discussion paper only, and will not tell you how to become a monitor engineer over night, but it will tell you how to cure the most common faults on the MTC9000. The Hantarex MTC9000 monitor chassis is probably the most commonly operated Video Game Monitor Chassis, the following instructions have been put together by 2 top engineers who together have repaired over 600 chassis over the last 9 years. A couple of tips before we start, 1st. Do not ignore the obvious, I have lost count of the times when I have seen engineers trying to track down some deep dark mysterious fault, when the obvious fault is staring them in the face, fault finding is a logical sequence of steps which does not necessarily mean doing lots of scientific measurements, but does mean using your eyes, ears, smell and common sense to track down the faulty component/s. 2nd. Be careful, on the red HT lead going up to the receptor on the side of tube, is 28,000 volts, on the degaussing circuit is full mains potential and on the chassis circuitry is 130+ volts, all three definitely bite and all three could kill you. When working, try to keep one hand away, making it less likely of making an electrical circuit, up through the arms and across the chest. Don't get complacent when working with these high voltages, they are out to get you, be warned.
First things first, check the chassis all over for dry joints, especially around areas where components get warm during normal operation, also check joints on the bottom of the Line-Output Transformer which from now on we will call the LOPT.
After checking the fuses and with all the chassis connected up, turn the power on and check to see whether the big 6" long resistor mounted on wire posts down the side of the chassis is getting very very hot, in normal operation this resistor will get warm but not so hot it badly discolours itself. If this resistor is getting very very hot and you did not hear the familiar crackle of the tube as it fires up, then you are well on the way to finding the most common fault on the MTC9000 which is the LOPT going short circuit, turn the power off and disconnect the power connector from the chassis. To change the LOPT it is first important that you discharge the voltage stored in the HT receptor of the tube. The tube will hold a charge, even when turned off for some weeks, so be careful. It is best to make some sort of DIY discharge tool out of a length of wire, a crocodile clip and a long insulated handle. The idea of this tool is that the crocodile clip is attached to some exposed metalwork of the tube surround, which in turn, is connected by the length of wire to a probe fixed on the end of an insulated handle. This probe should be designed so as to allow you to get under the HT cap, and short this HT connection down to ground via the metalwork. Once you are absolutely certain that the tube has been discharged, disconnect the HT connection, unsolder the ring of pins under the LOPT and then open up the tube base connector to expose the solder connection for the other thinner HT (focus) wire coming from the LOPT. After unscrewing the self tapping screw which hold the LOPT to the chassis, remove the LOPT. Fitting the replacement LOPT is just a question of doing the reverse of removing the old one, on some versions of the white tube base connector, the focus wire cover has to be fitted over the wire before soldering, this cover must be fitted otherwise the connection will arc over to near-by components. Before reconnecting the HT cap, discharge the tube again, because sometimes part of the charge can return, even after the tube has been disconnected.
Although I have said that we will not be doing a lot of scientific measurements, there is one that is important, and that is measuring the regulated 130VDC supply used by the monitor (this should never vary more than a few volts), which from now on, we will call the B+ voltage, the best place to measure this is by putting your red meter probe into one of the two middle holes of the connector on the chassis end into which the scan coils (coils fitted around the neck of the tube) are plugged into, and the black meter probe to the metalwork of the chassis. You will notice that on the plug from the scan coils, the middle two pins are linked by a short wire, the function of this link, is to disconnect the output from the 130VDC regulator circuit on the chassis, from the rest of the monitor circuit, should the scan coils be disconnected. If after taking a voltage measurement you find the B+ voltage is well below what is expected, then this normally points to three things, 1. there is a 22MFD 160VDC capacitor standing up in the middle of the chassis normally marked C34, which goes "leaky", do not try to meter this component, just change it. 2. the regulator circuit main power transistor has gone open circuit, this is mounted on the side of the chassis where the big resistor is, it you want to meter this component, do it out of circuit, the device fitted should be a TIPL762 although I know of some engineers who replace this for convenience sake with a BU508 (don't forget to re-fit the insulating pad behind the transistor, making sure it is insulating correctly). 3. up at the very top right of the chassis PCB is a 33K resistor normally marked R110. When they fitted this resistor at manufacture, they fitted to low a wattage version (1/4 Watt) and consequently it has a tendency to go open circuit without any visible signs of burning out. Once a higher wattage (1/2 Watt Min.) resistor has been fitted it is very unlikely to go open circuit again, meter this resistor out of circuit. One point to remember is that when making measurements using the metalwork as your black meter probe connection, it is important that the earth connection from the tube's metalwork surround, is connected the neck PCB board, this is normally a separate black wire with a small spade terminal at one end, coming from the braided earth wire held against the tube by springs, this should always be connected, when the chassis is powered up. If after changing the LOPT and checking the 3 previous typical faults, you still cannot get the chassis the fire up, then it may be that the BU508 Transistor (mounted on the metalwork nearest to C34) has gone open or short circuit, try metering this out of circuit (when re-fitting, don't forget the insulating pad, checking for burning).
If you find that the B+ voltage is to high and you are getting a wavy picture, then check that the TIPL762 transistor has not gone short circuit.
If the monitor will not run, try ZD1 this 12V Zener diode can go short circuit, thus shorting the supply for the oscillator IC TDA 2595.
If when you power up the chassis it blows the supply fuse straight away then this points to one or more of the rectifier diodes having gone short circuit. These are located in the top right hand corner and are marked D19-22 we normally fit BYV96C to replace these, but almost any 1.5 Amp 400 Volt silicon diodes will do.
If when the monitor is running you get a wavy picture which looks like 50HZ hum, then try changing the big smoothing capacitor on the power supply circuit, normally marked C53.
If when the monitor is running you get high frequency interference on the picture and this is affected by gently tapping the side of the chassis then check for dry joints, but in particular check the big centre earthing pin (if fitted) in the middle of the ring of connector pins, on the bottom of the LOPT is properly soldered.
If you get just a bright white line across the centre of the screen and no other image anywhere else, then your vertical scan IC (TDA1670) has most probably gone faulty, when this blows it will take out R94 as well (3.9 ohms) this resistor is buried down the side of the LOPT, we have found the value of this resistor to be not to critical, but it must be mounted away from the PCB as it has a tendency to burn, if a fault should develop. The supply voltage for the TDA1670 comes via D5 which should read approximately 26VDC when metered. If you cannot get replacement TDA1670 or TDA1670A chips, use TDA1675 instead.
If you cannot get full brightness from the screen, and the brightness changes with the image, and the B+ voltage is correct, then the 270K resistor normally marked R90 located on the far right hand side of the chassis, has gone open circuit.
If after checking the B+ voltage, you are getting white fly-back lines down the picture, then this indicates that the fly-back blanking circuit is not working, check the components associated with TR18, again buried down beside the LOPT.
If you have a white screen and no image then check the voltage across C205 on the neck board, this should read about 190VDC, if not check back to R126 + D15.
If after adjusting the controls you find that you cannot get enough width on the screen try changing C42.
If you get horrible interference on the screen, check that the ground connection to the video input plug is making good connection, this plug is prone to dry joints and cracking of the PCB around the area of this plug.
On some models of MTC9000 the video input is clamped by three 4V7 Zener diodes (very near the video input plug) these can go short circuit causing the loss of one or more of the colours, check these for short circuits.
Setting up the brightness of the monitor, once it is running correctly, should be carried out in the following fashion. Power the monitor up, set the brightness control (mounted on the bottom left hand side of the chassis, not on the LOPT) to the mid position and disconnect the video input plug. On the LOPT are two controls, one is the screen voltage control (often mistakenly thought to be the brightness control) and the other is the focus control. Turn the screen voltage control fully anti-clockwise, look closely at the front of the tube and slowly turn the screen voltage control up until a white hue appears on the screen, back off with this control until this hue just disappears, the screen voltage is now correct. Reconnect the video plug and turn the brightness control until a nice picture is up, you can now adjust the focus control (upper control on the LOPT) until the picture is nice and sharp.
That just about raps it up, if you would like to contribute to this document, or if you have written or writing a document covering other products/topics, then why not send a copy to us for possible distribution.
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WE HAVE TAKEN CARE TO MAKE SURE THAT THE INFORMATION CONTAINED IN THIS DOCUMENT IS SAFE AND CORRECT BUT I/WE CANNOT BE HELD RESPONSIBLE FOR ERRORS WHICH MAY BE CONTAINED IN THIS DOCUMENT, OR FOR INJURY OR DEATH RESULTING FROM THE USE OF THE INFORMATION CONTAINED WITHIN IT. IF IN DOUBT OF YOUR COMPETENCE OR SAFETY, DO NOT ATTEMPT THE REPAIR, SEND THE CHASSIS TO A SERVICE COMPANY, END OF DISCUSSION.