Ran into some difficulties exacerbated by my own stubbornness. Voltages were not good on the NE5532 U4 and U5. Upset, I asked for help on the Yahoo forum. I decided to step away for a week (had work commitments in any case.) Cooled down, heeded advice and got it fixed! Troubleshooting thread follows (tl;dr) …
Tue Mar 30, 2010 1:23 pm
I will appreciate any assistance with my Ft. Tut-80 build. Let me start by making an admission (#1): I measured voltages on V1 that were in error but questioned my results. As such I forged ahead with the rest of the build since the system seemed to behave correctly. I am sorry I did not stop and ask these questions.
Symptoms are follows:
1. Sidetone and Spotting function works
2. Was able to hear and establish VFO frequency on my “Big Rig”…currently set to 3584 (pending securing of L9 with wax)
3. No received signals
Things were proceeding fine until I go to the installation of IC4. I had been testing with a wall wart rated at +12V 4A. Admission #2: I measured the actual voltage and found it to be +17V!
Upon installation of IC4, voltages were not matching either there or IC1 (where they were fine before). As I mentioned, I continued with the build since the CPU-based functions were OK (I think I realize the errors of my ways).
I am not listing the voltages here in this message as I need to ask how best to debug. I have checked component locations and values and all look good. I have checked soldering and all looks fine. I have been very careful to make sure temporary connections have not been shorted. Transformers windings have been checked and counted.
Is it possible my mistake of running 17V has damaged a component? Is it possible the NE5532s were toasted somehow (U3, U4…and possibly U1). What would influence low voltages on U1 if this IC was not damaged?
I appreciate your thoughts (and don’t build your Tut-80 like I did. I did and now I have problems!)
Re: Troubleshooting Help
Should read U1, not V1. Sorry for mistakes caused by haste.
Tue Mar 30, 2010 2:35 pm
Yikes! I don’t want to be presumptious ‑but I am concerned about possible battle damage. Wal-warts are often envisioned to draw a lot of current, to bring the voltage down since these things typically lack regulation. The tut on receive of course draws tiny current.
The datasheet implies the NE5532 can handle 22 volts — but I can imagine some caveat’s involved.
I suggest waiting for someone more familiar with the design and components to guide you into locating what is most likely to be damaged. Even if you have NE5532 spares you could do damage doing an unnecessary repair.
To be a useful power supply to test projects like this — you must add a regulator with appropriate capacitors on it. A set of batteries with enough voltage can be used as a power supply, FWIW.
Lesson learned — check out all ‘unknown’ power sources with a DVM. I can imagine learning something new myself on my next trip to the workbench, if I pay attention.
Yes I did indeed learn my lesson. I was shocked (and ashamed since I know better…I least I thought so…) I am now only using a stiffly regulated bench supply.I accept possible battle damage as you say, but I don’t want to prescribe this as the failure mode either…at least concerning the op amps. I agree with you Curt, no unsoldering until I get some more input.
I do appreciate your comments!
73 Brad “trying to not let the blue smoke out” WF7T
As far as damage goes, I would think it would be pretty limited. First, check to see if the 5v regulator is working ok. Check 5v at pin 16 on IC6, the 74HC4053 mux part. I would expect that the 5v regulator is ok as it is good for 30v.If you can hear the sign on “v1” on power up, the PIC is ok and IC3 is likely ok.
If you have IC 3 and IC 4 installed and they are working ok, pin 1 on both IC3 and IC4 and in 7 of IC4 should be 5v. Pin 7 of IC3 should be 4.1v. If these are ok, the op-amps should be ok. The op-amps are good for 36v, so I don’t really expect a problem there.
The regulator protects a lot of things. The two places where you could have problems is IC1 (CA3086) which is rated to 15v, and the 11v filter transistor Q1 (2N3904). Check U1 pin 5 to see if you have about 1v less than your input supply. If the input is 12v, you might see 11v here.
If you see something like 5v either Q1 is blown or U1 is shorted or both. Let me know what you see.
If you could send your voltages for U1 as well as what you supply voltage is, I could see if there is a problem. The expected voltages are listed in the manual assuming a 12v input. Look at the voltages on page 13 of the part 2 manual on line. The voltages there are correct except that pin 5 ought to be 11v because L1 was not installed yet when that reading was taken. The problem is that with the VFO connected, these voltages will have both a DC and an AC component (due to the VFO running through it), so the voltages may move depending on how the AC voltages affect you meter.
I really do not expect 17v to affect that much (U1 and maybe Q1), so this should not be a huge hit.
- Dan, N7VE
Dan, thanks so much for taking time to review and respond. Here is what I measured…
Supply Voltage = 13.7v
Power up sends “v1”
IC6 Pin 16 = 5v
IC3 Pin 1 = 1.3v
IC3 Pin 7 = 4.1v
IC4 Pin 1 = 0.7v
IC4 Pin 7 = 0.3v
IC1 Pin 1 = 0.1v
IC1 Pin 2 = ‑0.3v
IC1 Pin 3 = 0.1v
IC1 Pin 4 = 0.9v
IC1 Pin 5 = 0.1v
IC1 Pin 6 = 2.4v
IC1 Pin 7 = 1.6v
IC1 Pin 8 = 8.6v
IC1 Pin 9 = 0v
IC1 Pin 10 = 0v
IC1 Pin 11 = 13v
IC1 Pin 12 = 0v
IC1 Pin 13 = 0v
IC1 Pin 14 = 13v
Q1: emitter 13v
Q1: base ~0.1v
Q1: collector ~0.1v
Some wacky voltages for certain. Your thoughts are appreciated…
73 Brad WF7T
The 5v regulator looks good, the PIC12F508 is good, IC3 must be ok, at least the second half. On the schematic, IC4B is biased from 5v from R16 and C20. Check the voltage at this point. That 5v biases IC4b, whose output biases IC4a, whose output biases IC3A. If the voltage input to IC4B pin 5 is low, this string of three op-amps in a row will also have a low voltage output. The output voltage of one stage should be the same as its DC input voltage which should be 5v. Look around R16, R17, R18, C22, C23, C21 for shorts, or bridges or to see if you have a joint you forgot to solder (it happens).
I take it that the input to Q1 (collector) is 13v and that the base and emitter are zero. Q1 seems either shot or has an open circuit. Check from IC1 pin 5 to ground and see if you have a short. The first two transistors in IC1(pins 1, 2, 3, 4, 5) do not look good. It may be that simply replacing Q1 will fix this. Transistor pins 6, 7, 8 of IC1 looks good. The other two transistors of U1 will not do anything unless the rig is keyed. If the finals are not installed, you can do the keying test and check these transistors.
If there is not a short to ground as seen from IC1 pin 1, replacing Q1 with any NPN type transistor of the same pin out (2N4401, 2N2222, 2N3904, etc) will work. This stage requires nothing special, just plain Jane generic NPN transistor. It is a ripple reduction circuit. Its goal is to provide additional isolation from the supply to the first couple of low level stages so that we can avoid feed back from the output audio stages to the input audio stages via the supply voltage (aka, “howl”). It helps a lot.
It may be that replacing Q1 is all you need. Q1 is easy to blow, but it is also easy to replace. If you don’t’ have a replacement part, I can send you one. If you use a replacement (like a 2N2222) Google on line for the data sheet for the 2N3904 and your replacement part and double check that the pin out is the same.
- Dan, N7VE
Took a while for me to get back to this due to work commitments. Dan, thank you for this.
For the sake of accuracy I identified and measures the voltages at Q1 (2N3904) as I thought I got them incorrect:
Q1 E: 0.14v
Q1 B: 13.05v
Q1 C: 13.05v
voltages at R16: 2.94v
Check from IC1 pin 5 to ground and see if you have a short = I measured open.
Taking measurements with a Fluke 8062A True RMS Multimeter…
I have not replaced Q1 as of this message (although I do have a stash of generic
NPNs of some sort.) Didn’t want to do that yet once I measured again at Q1 and
Solder joints look ok at this point and no shorts noticed in the areas you recommended searching.
Replacing Q1 seems like the next course of action, do you agree?
73 Brad WF7T
ah HA! Replaced Q1 with another NPN (an old Radio Shack 2N2222 clone I have had around in le Junque Box for years) and the voltages tested very nicely!
Connected to my G5RV and I hear beautiful signals from the Georgia QSO Party tonight. I must say I am very pleased at the dynamic range of this rig! Bone-crushing signals right next to ESP-level…I can hear them all without any nasty pumping and crunching. I knew this was going to be a great RX…totally exceeds my expectations!
I am going to finish my TX testing tomorrow, but wanted to report my success and absolute satisfaction…thanks to Dan and all…
73 Brad WF7T