Mtc 9110 keeps blowing F1 2AMP Fuse

[rfr341]

Just got an operation thunderbolt witha dead monitor. It is a 25" tube with a MTC 9110 chassis, when you power it up the the F1 2 amp fuse blows. What could be causing this? I have followed the flow chart for this chassis with no luck so far. Any ideas what to try?

[grantspain]

one of the diodes in the  primary circuit

[rfr341]

I have replaced  the diodes D21, D22, D19 and D20 which  I assume are the diodes in the primary circuit with no luck. Any other ideas?

[grantspain]

is the fuse blowing straight away and also black

[rfr341]

Yup, it blows as soon as you turn the power on and it is black.

[grantspain]

ok thats a dead short so should be easy to find
look at tr19,tr20

[rfr341]

I have checked the tr20 and it might be suspect so I have ordered a new one so I just have to wait for it to arrive, I'll have to loacted the tr19 and check that and get back to you.

[grantspain]

check the HOT also,common faults on mtc9000(very similar) were the psu transistor and the HOT going short circuit,sometimes it would manifest itself with the large load resistor glowing orange

how is the ptc connected in circuit on that chassis-does it have seperate fuse?

[rfr341]

I have checked the HOT and it looks good but I have ordered a few and will change that. Not sure what the PTC is , if you could expand on that I will check it. Just a quick question regarding the TR19 , what order on the transistor are the legs when it comes to base, collector and emitter for some reason I can't figure this transistor out on the order.

[grantspain]

PTC is positive temperature coefficient,it controls the degauss coil-its marked as PTC 1 on the mtc9000 chassis-if it goes short then fuses blow crapless

in regards to tr19 just google the transistor code and download the datasheet-always replace with exact match

[rfr341]

How do I go abouts testing ptc1 and I tested the tr19 and it looks to be shorted.

[grantspain]

you can meter the ptc,its a thermal switch so it should be open circuit

[rfr341]

Looks like the ptc is good, so now I am in a holding pattern until the parts I ordered arrive. I had to get them all on line because the electronic stores where I live are pathetic and don't seem to carry anything. I will let you know how things go once I get the new parts installed. Thanks for your help so far. 

[rfr341]

My parts have finally arrived so I replaced the Hot and the voltage regulator transistor and the fuses does not blow. But now the big 330 ohm resistor gets very hot and starts to glow orange, so I assume that means my flyback is shot, am I right on that? If it is shot where would be a good place to get a new flyback and is that resistor still good or do I have to change that also. If I have to change the resistor where can I find one, I don't seem to be having much luck finding a replacement when I look it up.

[grantspain]

could be flyback but check the transistors do not require insulated sheets between then and the heat shield

[rfr341]

The transistors do have insulators between them and the heat shield, also I am not getting a glow from the neck of the tube or any sound from it.

[grantspain]

i have had quite a few of the mtc9000 flybacks go bad
http://www.giz10p.co.uk/monitors/parts/hantarex-mtc9000-lopt-/-flyback-28021200-/prod_14.html

looks like hrdiemans make the flyback replacement

[rfr341]

The big 330 ohm 30 watt cement resistor looks to be damaged, the inside rod the coil is on is broken but when you measure it there still resistance so I don't know if i can still use it. I am not having much luck findind a replacement cement resistor with that high of wattage, but i have found an aluminum resistor that is 330  ohm 50 watt rating, can I use and aluminum resistor to replace the ceramic cement resistor? As for flyback I am going to be ordering a flyback and cap kit from bob roberts and hopefully that fixes the problem, I have tested all the voltage regulators and everything else  the flowchart shows which could be causing the problem and they ll seems fine.

[grantspain]

i have seen big ali resistors put on these chassis although i would suggest the original material for heat dissapation
if it reads correct then its probably ok