Hantarex MTC-900 Issues

[SirPeale]

My first Hantarex, so I'm unfamiliar with it.

Power on, it displays a yellow bright screen.  No picture at all that I can see.  Lines going thru the screen like the screen was turned up too high, but with the screen control turned all the way down.  Turn it up and it just gets brighter.

Both fuses are okay.  I wanted to measure B+ but wasn't sure where to measure it from.

Placing my black lead on frame, and the red lead on the large while resistor mounted on the left, I get 0VDC closest to the rear, but -30VDC(ish) on the other end.

Where do I go from here?  I'm stumped.

[Ken Layton]

The R.H. Belam Company in New York is the official Hantarex distributor/parts/service center: www.belamny.com

[SirPeale]

No ideas, eh?  Damn.

I have replaced every electrolytic cap on this.  Just an FYI.

[Ken Layton]

I have written a repair guide to the 900/E. There's a difference between the 900 and 900/E.

Remember that some capacitor polarity markings on the board may be incorrect on Hantarex monitors too.

[SirPeale]

Which caps?  I was very careful to put them all in the way I took them out, but I suppose I could have made a mistake.

What is the difference between the 900 and 900E? 

[SirPeale]

There isn't a label on this monitor any more, but I'm 97% certain it's a 900, not a 900E.

[qrz]

schematic here:  www.freeinfosociety.com/electronics/schemview.php?id=2244

check the collector voltages on TR28,31 and 34. ( rgb driver xistors)
per print , boost voltage at c51/72 should be > 200v
if voltage missing , check r131,145, b6 coil,d25
base voltage on TR27,30,33 should be 12 v . if missing , check IC4 ,D27, r116


qrz

[SirPeale]

Thanks, qrz.  Only problem is I don't know how to use them!  I can follow a diagram, identify components, but don't know how to use it to troubleshoot.

I'll try the suggestions you gave there.  I'll look up the data sheets on those parts to see which legs are collectors.

[SirPeale]

The R.H. Belam Company in New York is the official Hantarex distributor/parts/service center: www.belamny.com

As soon as I told them what monitor I was working on, they said "fogeddaboudit!"  They only deal with new stuff.

[Ken Layton]

Which caps?  I was very careful to put them all in the way I took them out, but I suppose I could have made a mistake.

What is the difference between the 900 and 900E? 

I've only worked on a 900/E. Never touched a 900.

[qrz]

  I'll look up the data sheets on those parts to see which legs are collectors.

many times the mounting tab will be tied to the collector ( to-202, 220 packages, etc ) 
the pin designations may also be silkscreened on the pcb....


                         tab

                   xistor body
                   printed #

                         leg

                        1 2 3
                        b c e

1 base
2 collector
3 emitter

 this order WILL vary per device number . research when in doubt

qrz
                       

[grantspain]

blanking problem,have you checked r59(2k2),r144(2r7)

[SirPeale]

blanking problem,have you checked r59(2k2),r144(2r7)

I have now that you've mentioned it.  They tested fine.

Someone on RGVAC mentioned that it could be a couple shorted color transistors.  Red and green together would produce yellow.  I examined the neck expecting to see three...and there are six.  They're all the same.

I started looking at my collection of TV chassis for transistors that would cross.  The original part is a BF871, which crosses to an NTE171.  I found a chassis that the transistor looked similar, so I crossed it - a 362-7 - which crosses to an NTE171 as well.  Regrettably only three on the neckboard, but at least I could eliminate one color as a possibility in this matter.  I chose red.

I removed the two red transistors from the Hantarex and replaced them with the ones from the junk chassis.  Replaced the chassis and fired it up...and instantly toasted R142.

[SirPeale]

It toasted R145 as well.  I plugged it back in after replacing R142 and it was glowing quite brightly.

I did note that the transistors I put in had slightly differing numbers underneath the "362-7".  One says "A23 514" and the other "A23 506" but I'm not sure what that means.

[Ken Layton]

I've heard that Hantarex can be very particular on replacement transistors. I'm told they must be originals and many times the NTE ones won't work.

I would suggest talking to Jomac in Australia about your problem. I think his new "Ultimate Monitor Repair" book at Star Tech Journal has a chapter devoted to Hantarex monitors.

[SirPeale]

Hm, that's a problem...they don't make them any more.  And they're rare as hen's teeth, no one carries them.  No one mainline, anyway.

I'll fiddle with this a bit more tomorrow.  It's late.

I'm not even sure if these old ones are bad.  I ran them thru the usual tests, they were reading funky, but I could have been doing something wrong.  I'll try again tomorrow.

[grantspain]

if you look at both datasheets you will see the pinout is different
nte171 is 1.emitter 2.base 3.collector
bf871 is 1.emitter 2.collector 3.base
thats why you fried the resistors

eBay Link

[SirPeale]

That's a darn good reason; why does the the NTE quickcross say it's compatible then?

[grantspain]

well if you twist the nte then it is compatible
i think you are missing a voltage,maybe meter the test points on the neck card using the schem as a pointer
i think 200v is missing
if this was a later chassis i would have said the lm1203 video amp ic is dead,this is the same fault but an earlier design using more components
there must be a common problem or some of colours would be o.k

as for hantarex,even the tech in the u.k does not support before mtc9000

[SirPeale]

well if you twist the nte then it is compatible
there must be a common problem or some of colours would be o.k

but if you twist the legs you'll touch them together.  I suppose I can be careful...but I bet that those transistors I put in there are toast now.

As for the yellow, if red and green were full on it'd look yellow, right?  I just hope it's not a tube fault.

[grantspain]

dunno could be a tube fault i guess,if you remove the green and red drive transistors and power on and still get a yellow screen then i would say thats a screwed tube
i still think its a voltage missing
an earlier reply from qrz will almost certainly reveal the culprit

[qrz]

That's a darn good reason; why does the the NTE quickcross say it's compatible then?

spec wise it likely is ..... there should have been a note about the pin orientation.

and be aware that many times an ecg/nte, sk (etc...) is more expensive than an original device .
and yes, exceptions do exist .

qrz

[SirPeale]

spec wise it likely is ..... there should have been a note about the pin orientation.

and be aware that many times an ecg/nte, sk (etc...) is more expensive than an original device .
and yes, exceptions do exist .

I was aware of the price difference.  NTE are usually much more expensive.  I always try to go original if I can.  The replacements I used were ones I pulled from a junk TV chassis.

I checked the specs after the fact and noted that it said there could be differences.  Too little to late I suppose!

[SirPeale]

I removed both TR27 and TR28 to see if the screen would drop a color.  It remained yellow.  I'm guessing a tube fault. 

I forgot I *do* have a rejuvenator, found it when I was cleaning out my van.  Problem is I don't know if it works or not.  I'll hook it up later and test it out.

[SirPeale]

I forgot I *do* have a rejuvenator, found it when I was cleaning out my van.  Problem is I don't know if it works or not.  I'll hook it up later and test it out.

So much for that idea.  It's a Sencore CR143.  Older than old.  It's got like 15 pages dedicated to which BW tube has what settings, and two for color tubes!

I could probably build an adapter...I've got plenty of sockets from donor TV chassis.

[qrz]

the cr70 has a "universal adapter" for the oddball crt . its terminated with test clips for pin attachment.
might do the same with the cr143  ?

yellow would be due to missing blue .   still would like to know the rgb collector voltages

qrz

[SirPeale]

the cr70 has a "universal adapter" for the oddball crt . its terminated with test clips for pin attachment.
might do the same with the cr143  ?

yellow would be due to missing blue .   still would like to know the rgb collector voltages

qrz

Where do I put the test leads?  Obviously red on collector leads...black on the frame?

Wouldn't removing the drivers from the neckboard turn those colors off entirely?

TR27 and TR28 are for red, correct?

As for the adapter, I've got a perfectly serviceable socket, some heat shrink, and existing adapters in a size I'll never ever use.  I'll build my own.

[Nipedley]

I had some trouble with BF871's on a hantarex chassis, I managed to get some replacement's from here..

http://www.cricklewoodelectronics.com/Cricklewood/product.php?productid=6986&cat=0&page=1

 

[SirPeale]

Dammit, all those links bring me to sites over the pond! 

[SirPeale]

If I did it right, the collector voltage was ~180VDC.  Still need to replace one of those resistors.

[qrz]

that means the 200v source is likely working .
now, are the collector voltages high or low on the other two output xistors ?

[SirPeale]

If I remember correctly, it was much lower than 200V.

[SirPeale]

Finally!  I think IC4 is bad.

edit: and I don't have one!  Crap.

[SirPeale]

They sell them @ Radio Shack.  Shocking, really.  $1.59.

But...the old one wasn't bad.  It read exactly the same way the new one does.  I was quite surprised.  Installed it with no change.

[SirPeale]

check the collector voltages on TR28,31 and 34. ( rgb driver xistors)
per print , boost voltage at c51/72 should be > 200v
if voltage missing , check r131,145, b6 coil,d25
base voltage on TR27,30,33 should be 12 v . if missing , check IC4 ,D27, r116

Collector voltages ~181VDC.  Same with C51.

11.8VDC on TR27, 30 & 33.

Since the boost voltage is supposed to be over 200VDC, should I turn up the B+?

[SirPeale]

I think I've eliminated the tube as a fault.  I had another tube - a 20" - that I hooked up briefly.  I couldn't get the yoke on all the way, but close enough so I could tell that the problem still seemed to be there.  That's a good thing.

But the problem still exists, so...

[SirPeale]

Removed TR30, now instead of an all-yellow screen I have one that's all red.  When I have a chance I'll pull the other to see if I get a blue picture of some kind.

[grantspain]

i think you are nearly there with this 

[SirPeale]

i think you are nearly there with this 

You think so?  Here's hoping.  Problem is I've already either removed or replaced the remainder of the color drivers, so I'm not sure what's going on there.

[SirPeale]

I'm going to have to give up on this unless anyone has any more suggestions.

All the voltages everyone has suggested have been spot on.

I've pulled every driver from the neckboard now, and it's still coming up with a yellowish screen if I turn the screen control up halfway.  Now, however, if I turn the screen all the way down the yellow goes away, and I'm left with a slight red hue with retrace.  That sounds to me like a red short in the tube.  Maybe.

I still can't get *any* kind of picture to appear, in any color.