NT-2701 no deflection

Mongo

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Soooo.... I started with a NeoTec 2701 with horizontal collapse (single vertical white line). I contacted NeoTec for schematics and saw in their block diagram IC401 and IC301 are both complicit in that circuit. So... I pulled the number off the schematic (mistake) for BOTH ICs and ordered them. Since both are high failure parts, I replaced them both and started troubleshooting.

I have now completely lost deflection in both directions. So I grab the old parts and find that IC301 on the schematic is listed as an NTE 7085.... the part I pulled was an NTE 7039. So... off to the parts store to grab an NTE 7039. Got it, replaced it..... and still no deflection. I pulled up the spec sheets and these two chips are WORLDS apart functionally. Anyone care to take a look and see if they can figure out what all I fried?

http://www.datasheetcatalog.org/datasheet/nte/NTE7039.pdf

http://www.nteinc.com/specs/7000to7099/pdf/nte7085.pdf
 
The only troubles I've ever had with 2701's were capkits and flybacks.

One thing I also learned about Neotec's: the manuals are riddled with errors! If replacing parts, get the numbers off the part that was installed on the chassis not what the manual shows.

In general, I would check for shorted diodes/transistors, cooked resistors, popped mylar caps.
 
Right... that is what happened. I trusted a part number given to me that turned out to be the IC for a 25" and not the IC for the 27".... and that put me in the position I am in now...
 
I've had horizontal collapes a couple of times on Neo-Tec's......it's always been the big polypropylene cap (shorted) in line with the yoke. Sorry, I can't remember it's location number. It's in line with the HOT, too.

Edward
 
I went to work on this over the weekend. I started by double checking continuity through my newly installed sockets with a meter. Found that I had bent two legs on one of the ICs on the board. I guess that's what happens when you are frustrated and in a hurry. I straightened that out and my vertical deflection returned!

As for the Horizontal... I traced that circuit and couldn't find any problems with transistors, resistors, or diodes. I ended up spending a lot of time looking at C423 (large polypropylene cap ELutz is speaking of right next to the yoke header) but physically, I couldn't find any damage. I pulled it anyway and it is split open on a spot I couldn't see.

Hopefully that is the problem. I'll know tonight after a trip to the parts store....
 
Problem solved. For future searchers:

NeoTec nt 2701 monitor displayed only a thin vertical line. Cap C423 removed and tested bad. C423 value is 924J 400V which indicates 0.94 Uf at 400 Volts. The parts store didn't have that value and rather than pay $20 from Betson, I bought two 0.47 UF 630 Volt caps, tied their legs together in parallel and BAM! Horizontal restored!
 
Problem solved. For future searchers:

NeoTec nt 2701 monitor displayed only a thin vertical line. Cap C423 removed and tested bad. C423 value is 924J 400V which indicates 0.94 Uf at 400 Volts. The parts store didn't have that value and rather than pay $20 from Betson, I bought two 0.47 UF 630 Volt caps, tied their legs together in parallel and BAM! Horizontal restored!

This is common on the NT-2702, also. I'd guess all the NT series. Don't let it run this way for extended periods of time. You run the risk of taking out the HOT, and possibly the flyback.....and yeah, I haven't been able to find a .94µf polyproplyene cap in several years, either.

Edward
 
Not arguing the point but looking for an electronic explanation: Why would running the monitor with only a single line be hard on the HOT and flyback? It seems like it would be hard on them since you are running one of the deflection circuits without a load but I see so many monitors with lines burnt in them I am lead to believe they can run a LONG time this way....
 
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Not arguing the point but looking for an electronic explanation: Why would running the monitor with only a single line be hard on the HOT and flyback? It seems like it would be hard on them since you are running one of the deflection circuits without a load but I see so many monitors with lines burnt in them I am lead to believe they can run a LONG time this way....

I'll be the first to say.......I'm not for sure why it can happen. All I know is it can happen;)
(experience speaking, there)

Honestly, I think it's a possible issue when that cap shorts (as opposed to when it opens).

Also, these crappy Neo-Tec's are the only monitor I've ever seen that will still pump when the horizontal retrace cap takes a shit. Every other monitor I've ever seen will go into shut down (barring a few old black & white models). Any screen burned line I've ever seen on a tube has been because of vertical deflection issues......NEVER horizontal. I wonder what level of x-rays those Neo-Tec's are putting out when that cap craps out......and the monitor is still pumping along!

Edward
 
Yeah... I can see it being hard on the HOT and flyback due to the lack of load for sure.

A shorted cap definitely likes to take other components with it.

Now that last part I can actually answer. Pin 12 of IC401 puts out the horizontal signal. That signal is used to activate the HOT which in turn powers up the flyback. That same signal also travels to the horizontal driver circuitry where it gets amplified and used to drive the Yoke. Since there is good signal coming out of IC401, the HOT stays activated and so does the flyback. The failure is post HOT but pre Yoke.
 
Yeah... I can see it being hard on the HOT and flyback due to the lack of load for sure.

A shorted cap definitely likes to take other components with it.

Now that last part I can actually answer. Pin 12 of IC401 puts out the horizontal signal. That signal is used to activate the HOT which in turn powers up the flyback. That same signal also travels to the horizontal driver circuitry where it gets amplified and used to drive the Yoke. Since there is good signal coming out of IC401, the HOT stays activated and so does the flyback. The failure is post HOT but pre Yoke.

Good info, there! I've never looked into it that closely. That kinda sounds like a bad design, to me. Do you own a geiger counter? Short that cap and take a quick reading!:D I'm now curious.

The handful of times I've had a Neo-Tec doing this.....that cap was a dead short.


Edward
 
A guy here at work (who helped design the cameras that were on the space shuttle) and I went over the schematic together. His assertion is that the HOT acts as a safety of sorts to shut down the flyback if there is no horizontal present. We did not go over whether that was to save the tube from burn or the flyback from running with no load. Either way, he seemed to indicate that it was possible to bypass the HOT completely even if it were dangerous to do so.

As for that cap which turned out to be bad, I will confer with him next time he is in the office and see what the purpose of the cap actually is. I am guessing it is used to buffer the horizontal signal and when it is shorted, the HOT picks up on the short via the collector which puts it into overload...
 
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