1084 and collapsed picture *fixed*

[dj_pirtu]

Got myself a 1084 yesterday but it's broken. Picture is collapsed in the middle. White line moves if I tune vertical and horizontal pots. I've used it only seconds so the line won't get burned on to screen.
I already looked for bad solder joints but will continue doing that. Have been googling about the problem and it can be almost anything, bad cap can be one reason.

Do you have any ideas where to start looking for the problem?

 

[DeluxePiantXX]

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[Kyle]

I have the same issue with my 1081 monitor.
I ordered a new set of caps hoping that changing them the problem will be solved.
In fact if I stay with monitor off for a long time the image come back on video but collaps again after few minutes.

 

[dj_pirtu]

This was working years ago and put away, and now this. It tells me it's cap(s), those die even not in use, or just because of that. And of course the IC (TDA2653A) can be bad too.

 

[powerGui]

Hello,

I don’t have much experience in CRT repair, but from what I see in the Dead Mac Scrolls, this “single horizontal line” syndrome is most likely linked to a cracked solder joint, or (at least on classic Macs), or it could be a burnt transistor on the vertical sweep circuit. It could also be the field effect transistor there.
Hope you can save your screen.

 

[roy_bates]

this is called vertical collapse

if it was me,i would check power first during a inspecton,if its getting power,then its either the vertical ic or some other problem

i do repairs,and this is a fairly common fault

 

[roy_bates]

and,if you can read schematics

there is a service manual for it,get it and look at it,itll help alot to find areas to probe for expected voltages etc

 

[roy_bates]

bad caps,is all i hear and see on the net

thing is most of the stuff i look at the fault had nothing to do with caps,it wouldnt be my first port of call,unless it looked bad or tested bad

 

[dj_pirtu]

Voltages are OK from the PSU, without cable connected to main board or cable connected. Voltages are the same, around +16V, +26V, +126V.

 

[roy_bates]

voltages come into the vertcial ic on pin 5,so check the voltage on either side of the fusable resistor R348

also as a side thought,becuase ive seen this happen,check the vertical size pot for function electrically and that iots actually connected to the board

 

[dj_pirtu]

There was around +12V in pin 5. Didn't find R348 yet... Vertical size pot is good.

But, R346 looks bad, 4R7 and it gives kilo-ohms.

 

[roy_bates]

sorry it was typo,that is the fuse

i suspect the vertical ic is dead

 

[roy_bates]

if you like checking caps there should be two caps on the other end of that fuse,id check those as well,to see if there ok and not shorted
its unlicky,but you never know

 

[roy_bates]

as a side note,all the hot ic's (parts that get hot)have thermal paste under them,i would suggest changing the paste,it may be obvious to some as its not just you reading this
the paste does dry up after so many decades

dont use cpu thermal paste,use the white paste,you with me?
i dont remember the code for the type at the moment,but if asked ill go look and come back and type out what i use it isnt anything special

 

[dj_pirtu]

Poked around with multimeter and didn't find shorts or anything suspicious... Swapped new resistor in there and it works. Been using it for an hour maybe, new resistor don't get hot.

Very good picture, actually better than on my other 1084. This has sharpness pot and scart from the factory where my another 1084 don't.

Need to repaste the IC, I think I have somewhere the white stuff. In finnish it's piitahna

 

[Kyle]

Great news, well donne
Can you show me where you swapped resistrors? In which area?
So I can try the same on my 1081 monitor.
Still waiting for the new capacitors...

 

[dj_pirtu]

I think 1081 is little different. R346 near the IC, it was burned. But why it burned, that's a mystery...

 

[roy_bates]

hey at least it was cheap,right?

i was honestly expecting the vertical ic to be dead

 

[roy_bates]

oh,by the wayi have seen the fuseable resistors go open,on their own for no reason
so there is that,i havnt seen them burn out like this though,that would assume a short,usually,you would probably agree

 

[dj_pirtu]

Paid - for this and with that cheap fix, not bad

Power button is going next, it turns on easily but powering off is harder.