Howdy,
New user here trying to get help with a failed 2700. The unit was working but the trace line was starting to go crazy with random zig zags and wild fluctuations in signals. It has now mostly stopped working although it does randomly show an inconsistent trace line that might span only an 1/8 of the screen width and then shoot across and retreat or just go away completely.
I asked Huntron for schematics or repair manual without success, although they must have them if they repaired their own products in the past. But I understand its all proprietary so here we are trying to figure this out from scratch.
Since the trace line from my understanding is an AC output signal, I have been starting from the connector trying to work back. I am only showing AC voltage at the probes in the mV range. I checked voltage at the 2w output power resistor. Again only showing erratic mV readings, this traced back to an output buffer (OpAmp, 634U) that I believe controls the output current. I again have erratic voltage in and out signals and the chip does have a proper DC supply voltage of I believe was 15v.
Since the input voltage is low and erratic I think the problem is further back, but I could spend forever trying to trace back to the transformer I am assuming. I do see there are 7 Voltage Regulators, 6 LM317 Mosfet style, all warm without to the touch and consistent so assuming they are all doing there job, then their are 2 'jellybean' BJT style voltage regulators that I can only assume work. There is no way to test them live as the risk of shorting is too high. I see test points all over the board, but again without a schematic I have no idea what any of them are tied to.
I didn't mention this before but the entire screen works normally and all the buttons appear to function correctly and the unit was working before the trace line become erratic and now mostly non existent.
Hopefully this might be a common failure and someone has a magic bullet to hand me :)
Thanks Again!
Sometimes you have to talk with the right guy. :)
I think these have been posted to the forum before but here they are again.
Main board (https://huntron.com/privatesales/technical/2700main-pca.pdf)
Test procedure (https://huntron.com/privatesales/technical/2700test-procedure-revE.pdf)
Absolutely Brilliant!
Thank You! ;D
Quote from: admin on September 24, 2024, 03:56:42 PMSometimes you have to talk with the right guy. :)
I think these have been posted to the forum before but here they are again.
Main board (https://huntron.com/privatesales/technical/2700main-pca.pdf)
Test procedure (https://huntron.com/privatesales/technical/2700test-procedure-revE.pdf)
Ok I have been testing and tracing for a few hours now and one thing stands out the most to me.
Everything DC seems to be working fine, and I have checked quite a few chips and I have the powers and grounds expected for the most part. Some outstanding issues I also encountered where the following:
On U46 the 5v VCC on pin16 was only 3.9, VEE on pin 7 read -4.9
On U49 5v VCC on pin 16 was 0.00V so I assume that is a problem and possibly tied to the lack of 5v on the following:
I am missing the 5v signal to all the source pins of Q5 through Q13. From the diagram these look like they should power the inductors which would then send a signal to the front banana jacks.
When I change the resistance selector 10,100,1k,10k,100k, that all triggers a 5v signal to the gate pins, but since there is no 5v signal on the source it never activates the inductors K3-k11.
When I run through the test procedure I fail on the voltage checks as there is no voltage present at the jacks. When I test for frequency all I get is 60hz, changing the frequency on the panel does not result in a change.
When I run it through the diagnostic procedure it passes on initial voltage checks but quickly fails on the offsets and will not proceed past this point.
Examples of this look like the following:
OFF = -32 -12800
OFF = -5 -3237
OFF = -11 -4257
OFF = -6 -2372
I can keep hitting proceed and I just get repeats or different figures but they all follow this same pattern forever. Actually, I didn't try forever, but probably about 8 times. Hold on now.....Ok so I can get past that but then it goes on to 'Set Compensation' and that just seems to go on forever without result.
Lets start with this. I have been on this for a few hours now so going to take a break and hopefully someone can guide me to the missing 5v signal?
Thanks in advance.
Vcc on U46 and U49 should both read the same (as well as any IC attached to +5VA) since they attach to +5VA. Are you seeing +5V at TP18 (+5VA at the voltage regulator)?
Yes, I have 5V on TP18.
Current Points Tested:
TP4 Oscillating 1.5 to 5.3
TP7 1.7 AC
TP14 0.0 ??
TP15 5
TP16 23 < 28
TP17 14.67 < 15
TP18 5 = 5
TP19 -23 < -28
TP20 -14.8 = -15
TP21 -4.9 = -5
TP22 4.99 = 5
TP23 3.3 = 3.3
TP24 31 > 30
TP25 9
Hello!
Check R158, R162 1kOhm 1%.
Check CR5, CR9 1N914 diode.
Check C14, C24 25V 47uF and C16, C19, C27, C72 0,1uF and C26, C70 25V 10uF.
Quote from: fetron on September 25, 2024, 11:12:24 PMHello!
Check R158, R162 1kOhm 1%.
Check CR5, CR9 1N914 diode.
Check C14, C24 25V 47uF and C16, C19, C27, C72 0,1uF and C26, C70 25V 10uF.
Ok so I am getting some weird reading on everything here and more. Not sure if my Fluke meter is not able to read things correctly but let me at least explain my findings.
On Resistor R158 I am reading 854 Ohm, far below the 1% rating
On Resistor R162 I am reading 964 Ohm, far closer but still out of the 1% spec.
Most resistors are returning expected values but some are returning half values or unexpected values that could be from being in circuit with other components?
CR5 and CR9 are not 1N914 diodes, they are BAT54 style diode. Regardless of style they are passing voltage both ways, and not just CR5 and CR9, but all of them on the board of the same part number are acting the same way. A couple will allow the voltage passing through to climb to 2.3v before the meter goes OL.
On Capacitors, I have a huge amount that are reading OL, others are reading far outside the expected ranges. Examples would be C14 and C24 reading 230uF, C15, C25, C28 reading OL, C70 reads 231uF
Literally almost every capacitor measured reads either OL or some unexpected value. I put a new battery in the meter and results are the same.
I would think that if this was some kind of systemic failure throughout the board I would have much bigger issues then just losing the trace line, but I could be wrong?
On the capacitors, its possible my meter cannot measure some of the finer .01uF values, but larger values like the 47uF should be pretty obvious.
I would really like to verify these diodes and capacitors, I need a solid confirmation of what is good or bad so I don't feel like I am in the electronics Bermuda Triangle of lost souls :o
Hello P3_Orion!
The components should be measured removed from the circuit. Otherwise, you will measure an incorrect value.
You could replace the capacitors and resistors named above without measuring.
If you still want to measure a capacitor, you must measure it with an ESR meter (e.g. U1733C or ESR70).
Quick update, I have ordered a dozen BAT54 diodes and am just going to replace them all. Since they are a SOT23 component, desoldering and testing them is fine but I might as well replace them while I am in there.
On the capacitors, its very possible my meter will not measure them correctly in circuit. I do have a capacitor/inductor tester so I will pull a couple suspects out when I tackle the diodes and test them on the cap meter.
Shame huntron won't support these any more, we would gladly spend the money to either have it factory repaired or even purchase a known good main board. We are a small shop and purchasing a newer unit is too costly and our older 2000 units are fading fast.
2000's have been the foot soldiers of the shop and have been going to 30+ years strong, but they are showing signs of dying soon. We really would like to get this 2700 up and running reliably.
I want to say thanks to everyone who has helped so far, will post up as soon as I get some parts replaced. Hoping its just a couple simple diodes, that would be cherry!
Well, I replaced all 16 bat54 style diodes, the other axial diodes tested good. Well its not fixed but it did make some progress I guess. It again passes all the voltage diagnostic tests, but fails on the other tests as before.
In the diagnostic menu if I select wave test, I at least get a line, its not a wave but its a line none the less so I at least know its capable of outputting the line to the display. I was briefly getting a partial line but when I grounded the probes together it did nothing and eventually just went away.
I put it in scan mode and alternate mode and I do get an alternating 5v signal on all the output transistors Q5-13, Except, Q11 has 5v constant and Q10 seems to be doing nothing with no voltage output.
Lets see TP4 that had a huge oscillation from 1.5v to 5.3 is now stable at -4.5 volts, interesting it flipped polarity.
C62 exhibits some odd behavior, it shows -14v on one side and -11v on the other. All the other caps show approximately zero voltage on one side and signal voltage on the other side, typically 2.5, 5, 14, 26, positive or negative, etc.. All the caps seem to be working, none are dead shorts or open, except maybe C62??
Other than that haven't made any progress really. Not sure what to do?
If there are any experienced Huntron gurus that think they can fix this board for a fair price I would entertain sending the board out for repair.
Okay!
On what side of the drawing is C62?
Quote from: fetron on October 04, 2024, 02:09:11 AMOkay!
On what side of the drawing is C62?
Looks like C62 checks out. Its tied to U53 which is the IC for brightness control which works just fine. The C62 is tied directly -15v and is in a comparison circuit for the IC. So no issues found so far.
Problem is I am unsure where to be looking for the problem. I know this is directly related to the wave form signal output the screen but I am unsure what drives that signal output.
Perhaps someone could point me in the right direction?
One thing I forgot to suggest you look at was F1 and F2. These are in the signal amp circuit located near the back edge of the PCB. Newer models had resetting fuses but older ones did not.
Quote from: admin on October 07, 2024, 01:52:49 PMOne thing I forgot to suggest you look at was F1 and F2. These are in the signal amp circuit located near the back edge of the PCB. Newer models had resetting fuses but older ones did not.
Thank You, fuse F1 (100mA) is indeed open, I do not see a F2 fuse (50mA). But I am at least in the right ballpark I hope, I will start testing everything within the signal amplifier stage and see what I can come up with. As a note I had checked that fuse but the device diagnostics testing did not flag any incorrect voltages so I assumed I was perhaps testing the fuse incorrectly, as I mentioned I am in the Bermuda Triangle of electronics repair where absolutely nothing is as it seems :(
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 :'(
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.
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.
Quote from: fetron on October 09, 2024, 12:48:06 AMHello 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
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.
Quote from: fetron on October 09, 2024, 12:24:13 PMHello 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
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.
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!
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!
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.