crossfire xp1400D tl494 specific voltages - diyAudio
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Old 26th July 2009, 10:12 PM   #1
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Default crossfire xp1400D tl494 specific voltages

I am looking to find out what the specific readings I should be getting at the tl494. The amp is in protection and was wondering what I should be seeing at pins 1,2 16,15 and possibly what circuit they are fed from. If my memory is correct: Currently null at 1, 4.99v at 2, 4.99 at 15 and 7.6+ at 16.
Also after looking through primer from Mr Babin, I see that I will get my hands on his dvd, it covers some really interesting topics. If the DVD is more thorough than his exhaustive posts, I know I will thoroughly enjoy it.
Thanks aot
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Old 26th July 2009, 10:41 PM   #2
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Post the DC voltage on each of the pins of the 494. Place the black meter probe on chassis ground. Place the red meter probe on the point where you need to measure the voltage. Copy and paste the following into your reply.


IC#
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:
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Old 27th July 2009, 01:51 PM   #3
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Quote:
Originally posted by Perry Babin
Post the DC voltage on each of the pins of the 494. Place the black meter probe on chassis ground. Place the red meter probe on the point where you need to measure the voltage. Copy and paste the following into your reply.

All measurements are +DC with grounding at neg input term of amp
IC# ti TL494 Board marking u1
Pin 1: 0.00 3.7ohms to ground (short?)
Pin 2: 4.99
Pin 3: 0.02 100ohms
Pin 4: 0.01 2.2kohms
Pin 5: 1.51
Pin 6: 3.71
Pin 7: 0.00 3.7ohms
Pin 8: 13.95
Pin 9: 0.00 240ohms
Pin 10: 0.00 240ohms
Pin 11: 13.95
Pin 12: 13.95
Pin 13: 4.99
Pin 14: 4.99
Pin 15: 7.66 fluctuating AC .074v
Pin 16: 4.99
I am a little rusty , sorry if this is just a case of shorted outputs (pin1), can't get test leads into transistors easily, tight amplifier still in case. Thanks for the help.
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Old 27th July 2009, 02:27 PM   #4
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is amp working in any way?
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Old 27th July 2009, 03:14 PM   #5
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Protection light in fan stays red never blue. No output or voltage on output or rails.
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Old 27th July 2009, 04:30 PM   #6
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The IC appears to be defective if the voltage on pins3/4 are correct. The voltages indicate that it should be producing output but pins 9 and 10 have no voltage. I'd replace the IC.
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Old 27th July 2009, 08:40 PM   #7
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Excellent, I was thinking the same thing but was reluctant to try due to SMD soldering involved. My old tenma solder station managed well though.

Yes, the tl494 was bad, amp fired up and almost fired up my test speaker.


Thank you Mr. Babin.
Could you briefly explain what was the voltage supposed to be on 3/4, 9/10 I closed up the amp prematurely. Just too happy to get it off my bench.
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Old 27th July 2009, 09:28 PM   #8
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Pins 3 and 4 must be below the top of the sawtooth waveform on pin 5 for it to produce output on pins 9 and 10 (in amps that use 9 and 10 as the output). Pins 3 and 4 can be driven directly. Pin 3 can also be driven high by the two internal error amplifiers (1/2 and 15/16).

When troubleshooting this problem, you confirm that the IC has supply voltage (pin 12) and ground (pin 7). If the IC has more than ~7v (pin 7 to pin 12), pin 14 should have ~5v.

If those are OK, you check 5 and 6. They should be approximately what you had in your amp.

If they are OK, then you look at 3 and 4.

If 4 is too high, it's likely being driven high by an external source.

If pin 3 is high, you have to look at the inputs to the error amp as well as external drive sources (often a PNP transistor connected to pin 14 of the IC). Pin 1 should be below pin 2 and pin 16 should be below pin 15.

For some amps, in good working order, 1 will be precisely the same as pin 2. This is because they are using that error amp for voltage regulation. I've never seen 15/16 used as the regulator but it can be used in the same way.

If pins 9 and 10 are being used as the outputs, pins 8 and 11 will have ~12v. Sometimes they are connected to the same source as pin 12, other times, they have a different source (direct connection to B+ or connected to B+ through a resistor).
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