Lost trace line on 2700

[P3_Orion]

Ok, so pretty much every test point on page 6 of the schematic is showing nothing, Fuse 1 is removed but there is nothing on either pin anyways. Never did find F2 ?? SMD perhaps??

All the IC's have their VCC, VEE and grounds, but do not appear to have any inputs or outputs, Its like the entire upper portion of the board is dead.

TP7 does show a small AC signal as measured before, but TP9, 10, 11, 12, 33, 34 all are essentially showing zero DC voltage.

I thought it might be the signal amplification circuit but it seems to go back much further, much much further. Uhgg 

[P3_Orion]

Sine Generator circuit on Page 5 checks out. On the sine out I measure 1.7 VAC at solid 2Khz, this checks out on TP7 on page 6. All the inputs and outputs on both U30 and U31 seem to check out.

I don't know if 1.7VAC is correct but the circuit appears to be working as expected from the schematic (pg5)

So moving the other direction to pg7, I am working on the fact I have no reference voltage signal going to any of what I assume are relays? So Q5-Q9 all seem to get the appropriate 5v signal on the gate when the different resistance settings are pressed on the front panel. I get the 5v signal to the source of Q5-Q9 and when one is selected that 5v goes to nothing as it is being pulled to ground, my assumption. This should trigger the relay, but there is not reference voltage to pass through to Resisitors 144-148.

So at this point it looks like IC U50 is working correctly, the transistors Q5-Q9 are operating as expected and potentially the relays K3-K7 are simply not getting the reference voltage needed to operate.

That takes me to the reference scaling circuit on page 6 which appears to be dead in terms of functionality. Looks like it might get a signal from a circuit on page 2?? I will have to check back later, I have to do actual work, so will check back in later. Also in terms of the reference circuit on page 6, R89 has no signal, both CR3 and CR4 both have +25 and -25v signals. I know they are technically +/- 28 but 25 is close enough for the moment.

[fetron]

Hello Orion!

On page 8, R179, R180, R181 (zero Ohm) should be checked (maybe open?).

Next step:
Switch on the Huntron 2700, set 20V / 2kHz / 100 kOhm range and measure +5V voltage on K3 relay coil pins
(do not measure on Q5 pins).
Is there voltage on the relay coils K1 and K2?

Next step:
How much do you measure with an oscilloscope at the TP8 test point?
How much do you measure on U46 / 3 pin?
How much do you measure on U46 / 13 pin?
I would like a photo of the oscilloscope measurement.

[P3_Orion]

Hello Orion!

On page 8, R179, R180, R181 (zero Ohm) should be checked (maybe open?).

Next step:
Switch on the Huntron 2700, set 20V / 2kHz / 100 kOhm range and measure +5V voltage on K3 relay coil pins
(do not measure on Q5 pins).
Is there voltage on the relay coils K1 and K2?

Next step:
How much do you measure with an oscilloscope at the TP8 test point?
How much do you measure on U46 / 3 pin?
How much do you measure on U46 / 13 pin?
I would like a photo of the oscilloscope measurement.

Hello and thank you for the help, it is much appreciated.

Resistors 179,180,181 are all intact and measuring 0.1ohms on my meter. Check Good!
Set the 20v,/2khz/100k, measure +5v, now I cannot measure directly on the coils since they are on the bottom of the board and I would not at this point taken the board out from the unit. Now measuring on the transistor pins I do have +5v prior to the relays. If I must take the unit to pieces to get this measurement then I will do so.

On U46, Pin3 = +0.035vdc
on U46, Pin13 = +0.035vdc (across from pin 8 counting upward towards pin16)

Pin 8 is a clean sine wave @ ~3.37acv

Image located at the following link: https://drive.google.com/file/d/1f75N0vrxHlkROPWaqEqptG-ZE0GoPvxB/view?usp=sharing

[fetron]

Hello Orion!

Switch on the Huntron 2700, set 20V / 2kHz / 100 kOhm range and measure +5V voltage on K1 and K2 relay coil pins.

Measure TP33 and TP34 with oscilloscope.

Measure R144 (both end) with oscilloscope.

[P3_Orion]

Hello Orion!

Switch on the Huntron 2700, set 20V / 2kHz / 100 kOhm range and measure +5V voltage on K1 and K2 relay coil pins.

Measure TP33 and TP34 with oscilloscope.

Measure R144 (both end) with oscilloscope.

Hello Fetron,

So since you asked again I took the unit to pieces and got her fired up and checked the 5v signals on K1-K2-K3. I will attach a link to a video that shows me grabbing the 5v signals best I can. Hopefully that's enough.

TP33 and TP34 as I previously mentioned are dead and the oscilloscope confirms this. R144 has ~3mV signal on both sides of the resistor.

Video of checking 5v on relays: https://drive.google.com/file/d/1_WeVqjJAJECQ9r3VnyWAFsXxFdlr9LLS/view?usp=sharing

Oscilloscope setup @ 500mV

TP33: https://drive.google.com/file/d/187LpcNQeBZblsnv8XN7sRww4mmp1hvGY/view?usp=sharing
TP34: https://drive.google.com/file/d/1UsVsMMWk3dho9eKIhNJS6U9yVN1L54CG/view?usp=sharing

[fetron]

Hello!

You wrote that +28 / -28V you only measured +25V and -25V.
Switch on Huntron 2700.
You should try to increase the mains voltage (from 110V slowly to 120V) with a variac transformer.
Meanwhile, measure +28V / -28V. As soon as it reaches a good value, stop increasing the mains voltage.

Huntron 2700, set 20V / 2kHz / 100 kOhm range
Measure the points marked with a question mark with an oscilloscope.

Measure +28V / -28V and +15V / -15V with an oscilloscope.

Next: Switch off Huntron 2700.
Measure the capacitors, diodes and resistors shown in the drawing.
If these are good, AR14, Q1, Q2, AR7, AR12 may be faulty.

[P3_Orion]

Hello Fetron,

Thanks for the help on this situation. I have ordered all the parts you have suggested might be faulty, in addition to several new fuses. I think first step will be to pop in new fuses and make sure I aint chasing my tail. If they pop again I am just going to replace all the parts in the circuit you suggested and go from there.

Most likely update mid week.

Thanks Again!

[P3_Orion]

Alrighty then....

Hey Dummy, if the fuses are blown replace them first, DoH!

It appears to be working now. I ran it through the diagnostic test procedure and it runs all the way through without issue and using the Huntron ASA test board I am getting what I would expect to be good signals. I have not yet compared with our 2 workhorse 2000's.

I do have yet another question, the signal line on the display is 'pulsing', is this normal behavior for the 2700? (We bought this machine used and it has never been used since it was not working so we do not know what the expected behavior is supposed to be.)

Personally I like the green phosphorous displays, no flicker, no pixelation, no pulsing. Just good clean signals. We also have VI Curve Tracer setup on an old Tektronix and it is bright, instant response and super clean signaling.

I want to thank everyone who has helped in this thread!

[admin]

Good job! The 2700 was our first Tracker with a LCD and was not very good as far as display speed. If you are used to CRT Trackers than the 2700 is less than stellar.