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With TD NULL, the engine having a good start TIT(800°C) and a good acceleration, whereas during Auto start the engine start TIT Struggling to reach the 700°C with a very slow acceleration.

Is there any possibility that the malfunction is related to a defective TD valve?

If so, is there any technical clarification to this point?

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The TD Valve is not your issue. Our books have a "desired" (not a limitation) of 780-810 for a NULL start. You have a good NULL start so look at the TD amp settings.

Quick check can be made by watching (listening) to the TD valve and place the switch to AUTO, you should hear the motor driving you TD valve to take fuel. If if does check your TD amp Start temp limit (830) the pot on the amp may have been "twisted" too far and gone all the way around. This can cause the TD amp to always think the temp is TOO hot and drive the valve to take fuel...

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NATOPS1: The TD Valve is not your issue…

Tusker: I would consider the TD Amp…

Lkuest: Seen the TD AMP do it many times…

Herc308: Sounds to me that your start pot in the amp is u/s.

No doubt;

So, I will keep the “Two TD Valves†attacked by my brothers during this weekend-by the help of the TD tester-as a “Semi serviceable Items†especially when the last one changed was accompanied by “minor†adjustment of TD Amp. Which make the bird to fly.

Note: my next move is to test the “TESTERâ€.:confused:

Thanks to all for the inputs.

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By tester do you mean the box or operator? We had a problem a while back with several of our testers. They kept saying part A was bad, that part would be replaced and come to find out it was part B. Every single tester had bad cables.

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I have recently had a rash of extremely high AUTO starts, AUTO T/O TIT, and fails NORMAL LIMITING check. All

are using solid state amplifiers. TD amp is driving the valve to PUT condition. I have also had an instance where

the Y-box leadset was damaged. Y-box shows everything on the numbers, but on startup AUTO TIT is 830°C,

take off will happily go past 1083° with the throttle still well short of the stop. NORMAL LIMITING check just

overtemps with no TIT cut-back. RICH/LEAN check shows a 50 - 60°C lean

Before I figured out what the problem was, I recalibrated the cells indication system, installed my thermocouple

swap-over relay, and generally spent a lot of time chasing my tail. Also slaved in various relay boxes, J3 leads,

on one occasion a coordinator, and another occasion a TD VALVE, and even thermocouples, t/c harnesses, T-blocks,

and y-lead.

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By tester do you mean the box or operator? We had a problem a while back with several of our testers. They kept saying part A was bad, that part would be replaced and come to find out it was part B. Every single tester had bad cables.

Was this the TD tester? I know you stated the cables were bad, but our indicator is in the tester. Please let me know if you have any problems with our part!!

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Since your engine is starting normally with an 800 degree null start the problem is more than likely to be your TD AMP. Using your TD Amp Tester will assist you in determining the condition of your TD AMP. Follow the entire procedure and not just the potentiometer adjustment section since accomplishing the entire check will test everything in the TD System. Failure to follow through could lead you down the wrong troubleshooting path.

If you are using the Raven or ABB TD Amps (Square) you can actually turn the potentiometers where it seems to have little effect on adjustment. The TD Amplifier Test Procedures are in the 1C-130H-2-73JG-00-2. Pay attention to the note that states some potentiometers may require 15 turns or more to bring to the null position. Following the procedures will bring you back to the point where you can adjust the potentiometers successfully. Lastly, occasionally a TD AMP will actually cause an engine to quit in LSGI if the Start Potentiometer is defective. TD System problems are can be perplexing since what you do to fix an issue one time may not fix it the next.

Good luck!

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By tester do you mean the box or operator?

I mean the operator Part No 6798233.

"Let off " Plaprad,..... I couldn’t resist.

Thanks to ALL for the help.

Anyhow, “Tragedy†started as follow:

Defect was raised on the “Form†With TD Auto:


TP: 12,000 13,000 12,700 12,500

TIT: 1,000 1,000 1,000 1,000

FF: 1,300 1,500 1,350 1,350


TP:12,000 13,000 12,700 12,500

TIT: 970 945 970 970

FF: 1,200 1,200 1,200 1,200

With throttle No.2 “one knob†back than others.

Which mean to me, that the defect we should track is on the TIT indication system, (thermocouples, T-block, harness, etc.) nothing else.

But.., anyhow “team1†received the A/C (no records if they “finger†anything before deciding to use the “TD Test set†Part No.20-6798233

During the TD Amplifier Test Procedures, indication revealed to them was:"failure of TD valve".

“TD Valve1†replaced.

After replacement, engine started (auto); max start TIT was 700°C with very slow acceleration and with RPM stagnation… NULL start was good TIT 800°C with good acceleration to ON SPEED.

New TD AMP replaced; defect of low TIT during Auto start remained as it was.

TD AMP swapped with a known good one, defect remained.

“TD Test Set†connected by “team2†History repeated, TD Valve also failed to pass.

“TD Valve2†replacedâ€, TD AMP adjusted. Defect cleared.

Today a recheck was done to verify the TEST SET operation by connecting the Test Set to a known good engine, all steps of the test passed.

Whereas when the Two TD Valves "previously removed†connected to the same engine, they re-failed to pass the TEST.

As I have “NO Experience†of using the Test Set, I cannot confirm the issue concerning the accurate steps that had been taken by our “Test Set Operators†during the test. But the Steps that had been failed are related to:

1-TD Valve Take To Null Time.

2-TD Valve Put To Null Time.

Main Point of the issue is; my understanding of how system works is disturbed besides losing two costly components.

My understanding that during NULL operation there is no any signal imposed on the TD valve (pure mechanical orifice setting 20% bypass) meanwhile with AUTO selected, during the starting phase the mechanical orifice setting will remain fixed unless singled/actuated by the AMP.

The only possibility that might explained that defect is: if the TD valve once TD switch selected to AUTO it becomes in ARM STATE and due to valve motor failure it starts moving to “TAKE†position. Which neither I read it nor experienced it before.

Note: Engine T56-A-15 / TD AMP part No. 5502636-2/5502636-4

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  • 2 weeks later...

The answer has already been given, but I just wanted to add a tid-bit of followup information for the original poster since he seems fairly new to mysterious engine troubleshooting:

Typically, when I respond to a red-ball for a hot start, I do the following events (a few alterations if necessary):

#1 Of course, shut down the affected motor, #3 engine, for example.

#2 Have them start it in Null. If you get a normal start, then your Hydro-Mechanical (TD Valve) is functioning properly, since NULL takes away the engine temperature computer (TD AMP!).

If it STILL hot starts, then swap TIT Gauges with another engine's TIT gauge (so, #3 gauge is suspected bad, swap it with #4 gauge). Usually at this point, I will have them shut down another motor so I can swap gauges. Start the suspected motor (I do this in Auto, I want to see it again): If it starts fine, then obviously you will start #4, and you'll probably see a hot start. This usually only happens with Cold Starts, as usually gauges like to LOSE indication instead of GAIN indication.

If it hot starts in Auto, and Null, you probably have a TD Valve or Fuel Control Bellows issue, but do not ignore your TD Amp, as it could be sending bad signals, etc.

If it hot starts only in Auto, you most definitely have a wiring, or TD Amp problem; I like to shake wires as much as possible when testing the TD Amp. Also, testing the TD Amp does not show the problem every time. Someone here said the 130 will make a liar out of you; it's true. A lot of times, if I find no other problem, still get a hot start, and the Y-Box (TD AMP Test Set) says it's fine: I'll change the TD Amp anyway, and on several occasions it has fixed it.

If you do restarts, and it doesn't hot start again, then I'll note the wind outside, as well as keeping detailed note in the log book in expectation for it coming back; in which case I will a TD Amp more likely.

This is covered in better, more accurate detail in the 1c-130H-2-70FI-00-1-1. Block 985 if I remember correctly.

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If it hot starts only in Auto, you most definitely have a wiring, or TD Amp problem;

Wrong!! A messed up TD valve has done this to me before. Cost going back over 5 TD amps to verify they were

actually good. For the same price, sticky FCU bellows can have you chasing you tail

Someone here said the 130 will make a liar out of you; it's true.

It just did! If your 5th & 10th bleed valves are closed, you should hit 810° at about 35% rpm in AUTO, at which point

the engine will bog down if the TD system is strong. Alternately, if you are in NULL, you'll be passing 900°C before you

could get the condition lever to STOP or FEATHER.

Don't be fooled by the obvious - double check EVERYTHING, look at (and see) what your gauges are telling you

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Thanks for the feedback and for the steps and tips you gave.

But the enquiry from my side that I was looking for an answer to it is a bit different. Defect issue definitely is not a HOT start in Auto/Null or in both.

Defect issue was:



Engine defect repeated many times during the starts, hot or cooled, head or tail, and the slow acceleration was confirming the actuality of the low TIT indication…..

1- Out of using the TD TESTER; is there any steps/tips to spot the defective component of this specified defect?

2- Is there any possibility that the culprit of this specified defect can be the TD valve?

If the answer for the last is “YES†I request technical justification from the expert brothers.

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Yes brother,

Might be intermittent, but the airplane now on stable condition after changing the TD valve and adjusting the TD amp, so, wise not “finger print†that cable.

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