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#1
Out of Production Hardware / Re: Lost trace line on 2700
Last post by fetron - October 09, 2024, 11:57:42 PMHello!
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.
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.
#2
Out of Production Hardware / Re: Lost trace line on 2700
Last post by P3_Orion - October 09, 2024, 05:13:57 PMQuote 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
#3
Out of Production Hardware / Re: Lost trace line on 2700
Last post by fetron - 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.
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.
#4
Out of Production Hardware / Re: Lost trace line on 2700
Last post by P3_Orion - October 09, 2024, 12:05:45 PMQuote 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
#5
Out of Production Hardware / Re: Lost trace line on 2700
Last post by fetron - 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.
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.
#6
Out of Production Hardware / Re: Lost trace line on 2700
Last post by P3_Orion - October 08, 2024, 12:58:40 PMSine 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.
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.
#7
Out of Production Hardware / Re: Lost trace line on 2700
Last post by P3_Orion - October 08, 2024, 12:11:43 PMOk, 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
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
#8
Out of Production Hardware / Re: Lost trace line on 2700
Last post by P3_Orion - October 08, 2024, 11:25:07 AMQuote 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
#9
Out of Production Hardware / Re: Lost trace line on 2700
Last post by admin - 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.
#10
Out of Production Hardware / Re: Lost trace line on 2700
Last post by P3_Orion - October 07, 2024, 11:39:23 AMQuote 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?