Hantarex MTC 9000 Squealing

[Nipedley]

Alright xD Now I've fixed the blue transistor issue, yesterday after a bit of a playtest (which went fine) I noticed a really loud quite bad static-squealy type sound.

This morning I turn it on and the sound is horrendous. What on god's earth has gone wrong now? Not having much luck really am I..

I thought anode, but there's no visible sparks and I made sure it was on tight yesterday. That and the fact that it was working alright last night and wouldnt just suddenly become loose, cant see any around the flyback but that doesn't rule that out?

Any ideas guys Bought this chassis as 'repaired' as well xD. Awesome stuff.

Video w/sound 4mb; .WAV sound 50kb (not as distinguishable) www.nipedley.net/CIMG4396.WAV

Just to say, there's no picture and according to my mum (not taking my finger off the power button and I can't reach to see) - there's no life in it at all, which would lead me to think maybe the LOPT's failed? Any help is much welcomed..

[Nipedley]

Alright I've given in and decided to send Mr. 'Squealy' chassis off to Giz10p for a professional repair. They had good rates, and with so many continuous failures I couldnt say no. I'm keeping the 'sync' chassis for whenever I get bored, as that thing is just a paradox

Hopefully the 'squealy' chassis will get a nice service and finally put this damned thing to rest!!!

[grantspain]

let us know what craig finds with this,all i can think of is some kind of problem with the flyback or that its a freqeuncy squeal

[Nipedley]

Well, I did some more testing with it (sending it off on Monday so thought I would have a go). After a bit of a warm up, the picture comes on but there's a definite issue with it. It looks almost like the picture is only being drawn at half the speed it should be, every other line being black instead of the correct colour, vertical frequency was also off. Still squealing like mad.

Oddly enough, I did a load more work on the 'sync' chassis and plugged that one in and that one is squealing too! Not as bad, and the picture looks fabulous (because all the components are near enough brand new now). I notice that the squealing gets much, MUCH worse whenever there the screen fades to black.

Very, very odd. o.o

Just to note, the 'sync' chassis still is out of sync. I've replaced just damn near about every component on it so I'm giving up hope for that =P It's odd, just this morning I found 2 dud resistors and replaced 3 new capacitors, including the mains smoothing cap which was the wrong value. And it still wont sync xD.

[grantspain]

both squealing,hmmmm
possibly a broken sync wire
what happens when you adjust the horizontal hold,does it affect the squeal?

[Nipedley]

I dont know, I'll have a check in a sec. I was just out again to have another look and I noticed that when the screen is full white (from the game signal) then the squealing stops entirely, then the white screen fades to black and it's horrendous. Possibly a transistor (HOT?) issue? I could try replacing all those as well. If I did those, and the LOPT, and my 'sync' chassis would be brand new xD.

I'll go check out the horiz. hold

[Nipedley]

Right well the horizontal hold control doesn't seem to be making any noticeable difference, the noise seemed to have lessened (presumably because it had 'warmed up') until the picture faded to solid black and again was faced with the noise you get from a snowy screen off a regular television.

I'm sure this is a frequency squeal, as when the white screen appears and the squeal fades I can hear a high-pitched tone in its stead. Is a frequency squeal indicative of a faulty transistor?

[grantspain]

hmmm,
i saw a polo chassis do this once,trying to think of the solution-something to do with the +25 volts to the frame i/c i think(not sure)

[Nipedley]

Well, there's that and there's the problem of it still being out of sync. I've replaced every capacitor, and every resistor is good now (replaced about 5 of them). The neckboard transistors are all replaced. Both of the IC's (TDA2595 and TDA1670A) replaced. The flyback and the HOT, and another transistor mounted to the metal frame, and some of the smaller transistors are just about all that havent been replaced yet.. I've also reflowed all of the connectors and miscellaneous wires going about the place.

Never thought that £120 hunk-o-junk in the local market would take me this far

[grantspain]

i reckon you have a broken track somewhere on the sync chassis,its the only possible thing after all the parts you have changed
did you connect the squealy monitor to the bottom signal to check

[Nipedley]

Possibly, I spent hours peering over it though trying to find something amiss. The only real problem on it was the filter cap being wrong, other than that and a few aged parts it's pretty good. It's that battle in my mind now that, with the squealy chassis being sent off to be repaired, do I still keep working on the sync chassis or give up. I don't like giving up and after all the work I've put into it, but then, I'll have a working monitor so it'd be fruitless. Deep stuff

If I do go for it, I'll order the new transistors and flyback and have a peer over the track. I'd die if it still didnt work then xD.

I did check the sync signal and all its connections throughout the board as a last measure, and the connect-up today seemed to chuck that out of the window. There is broken track, where a previous tech messed up and lifted the track around the flyback but he soldered a jumper into it and that couldnt have too deep implications on the sync could it? Even so, I wouldnt know a better way to fix that.

Looking forward to getting the other one back from craig I must say!

Oh, and the bottom signal? I'm having a blonde day

[grantspain]

the bottom monitor video signal
its def not flyback or hdt or power related
its gonna be something so simple that when you find it you're gonna swear

[Nipedley]

Haha that sounds very likely. Yeah the squealy monitor was on the bottom signal as well (they're both chassis for the bottom monitor), and it worked fine, including the sync (only the blue issue which I fixed) until it decided to die on me a few days ago. Top monitor's never given me a minutes trouble You can bet as soon as I get either of the bottom ones working, the top one will go the next day!

Well, at the least by the end of next week I'll have a newly repaired 'squealy' chassis back from craig to use with it. With a bit of luck i'll diagnose the sync chassis by then =) I'll pull her out at some point, probably tomorrow when I get bored and have another look over.

Just thinking, when I first bought this machine I'd never even touched a soldering iron xD. Oh my. At the least, it was/is all good practice for my a level electronics class

[Nipedley]

I found a flowchart from randy fromm suggesting that c17-20 & 22, and transistors 10 - 13 might be an issue so I've ordered replacement parts for those due in tomorrow.

I've decided to focus all my efforts onto this chassis, as I pulled out the squealy chassis today and after a bit of a look over it's horrific. There's a resistor that's black at one end, one of the ic's is completely wrong and it's metal clip holding it in split in half, the big ceramic resistor looked black and I poked it and it crumbled out onto the table xD.

So yes, the sync chassis is my main focus now. I had an idea it might be something in the remote-board circuit (the v.sync part) but everything seems good, only there's 1 resistor I can't read so I can't check the value. It's code is 'Brown red black red brown' o.O. Once I've checked that, and replaced every transistor I can find tomorrow, I'll give her another fire-up.

P.S. you wouldnt happen to have any schematics for this version of the chassis? I have the 'regular' one in many forms, but not even the parts list conforms. I.E the ceramic resistor the schems could be listed as R109 and on my board as R34 >.> Not helpful for checking I have the right values in the right places!

[grantspain]

you better show us a pic of your chassis,r34 should be a small resistor

[Nipedley]

That wasn't a specific example, just a random one But that's what I've encountered consistently. I can check the components that are already installed, but I can't be sure they're what was meant to be there originally because the schems and the board dont match at all. That's why I'm worried I can replace as many components as I like, but I'll never be able to fix it without proper schems.. Hopefully I'm wrong.

For example, my neckboard has at least a good 20 resistors on it and the schems only list a few.

For the sake of it, here's a couple of chassis shots =)

[grantspain]

not seen that chassis before,it is a mtc but not a 9000
clearly there have been some serious modifactions done
very importantly where are the clips for the hdt,east/west transistor and the frame ic-all of these will over heat and i can't see the insulation sheets behind the hdt and frame ic
there has been some bad tinkering with this chassis

[Nipedley]

Oh dear That's what I like to hear!

If its not a 9000 it's darn close, between this and my 'proper' 9000 (the squealy one) the sub-systems seem to be mostly identical but with components in different places on the board.

I have the clips stored for when I'm finished, as I'm prepping all the transistors for replacing tomorrow. The insulation is there also =) (If a little tattered)

I''d be very interested to find out what model this is, then. I always thought it was rather odd. Prototype maybe?

The only reliable way I've found to identify what components should be is following the actual schematics, as more of than not (but not always) these match up

[grantspain]

could be an early production run,yes its very similar to a standard mtc9000 apart from the large metal resistor strapped to the frame and the transistor near it
this may have been modified for the smaller tube
the key to your success with the sync is tracing every track and checking continuity

[grantspain]

you have checked the sync switch is not knackered?

[Nipedley]

For what I can tell, the resistor on the frame is doing the job of the ceramic resistor on the other chassis - it's listed as 330 ohms. That transistor near it is typically on the board as well (TIPL762A or something like that) only for some reason this time it's mounted and connected by wires o.o.

I know it works for negative-positive switching, other than that I can't be sure. I know that when I switch it to positive, the picture goes very very wrong

[grantspain]

when you get this back together if it still shows the problem can you post a pic of the screen

[Nipedley]

Sure thing, transistors should arrive today so life pending might have her back together tonight if not tomorrow

Here's something I always thought a little odd, at least once when the screen rolls over, when the "top" of the picture is about halfway these lines (above the 'top players' in the picture) would always show up around it. I never figured out what would cause those.

[Nipedley]

Oh my god xD. It works! It actually works o.o I can't believe it xD.

After my 4th mega-repair (replaced 18 components today, including all 4 major transistors and every 548B and 558B I could find - I think it was one of those that was the problem). The only component not replaced left is the LOPT. So much work. But it was worth it, because I essentially now have a brand-new monitor

Included is a picture of the newly installed monitor. It's not all set-up properly but it is half 9 and I have school tomorrow so I dont have the time. And also, a picture of the leftovers of all the components I took out in the 4th 'mega-repair'.

Ahh, I'm happy. Thanks to everyone who helped out (especially grant, been there all the way )

[grantspain]

well done bud,you beat it

[Nipedley]

I just wish I knew which of those little b******* it was so I could keep it as a momento. I never thought one of those would be the problem. But it's all over at last xD.

[grantspain]

the experience you have gained is priceless,although this has been a hard slog i think it would have been difficult even for some of the most experienced techs to repair such a delicate fault
you should be real proud of yourself,if i ever come back to the u.k i want you to be my trainee