Recent posts
#21
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.
#22
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
#23
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
#24
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.
#25
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?
#26
Technical Support Announcements / October 2024 Tech Support News...
Last post by admin - October 07, 2024, 09:07:22 AM #27
Obsolete Software / Re: workstation 3.5 and window...
Last post by Al1234 - October 05, 2024, 08:19:22 PMthis was very helpful tonight. about a couple of years later. thank you so much for keeping these up.
#28
Out of Production Hardware / Re: Protek 1
Last post by Al1234 - October 05, 2024, 01:32:38 PMI remember I had no trace on a KJ3, I made some adjustment for trace alignment in both the advanced mode and regular and on the inside board (3 potentiometers on the tube board mounted vertical to the left of tube) turned up the intensity and move right, left, up, down and trace appeared. I think one of those potentiometers makes the trace completely fade away.
#29
Out of Production Hardware / Re: Lost trace line on 2700
Last post by fetron - October 04, 2024, 02:09:11 AMOkay!
On what side of the drawing is C62?
On what side of the drawing is C62?
#30
Out of Production Hardware / Re: Lost trace line on 2700
Last post by P3_Orion - October 03, 2024, 05:37:15 PMWell, 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.
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.