Getting There
Page 1 of 2

Author:  ecpilot [ Sat Jan 26, 2013 5:14 pm ]
Post subject:  Getting There

I have the bias set for the final amp and it seems to be working, sort of. I get about 30 watts out but only when I probe J16 or J17 or some of the surrounding components with a DVM or scope probe. C45, C37, C38 or the pads where resistors R34 and R35 also when touched by a probe will allow the final amp to generate RF. Without touching any of these areas, the transmitter just keys on and off without putting out RF. Sometimes touching J16 or J17 will cause the radio to just cycle meaning it tries to output some RF for a split second and then shuts down and restarts like a cold power up. I don't know why touching these components (and probably some others I haven't found yet) would cause the radio to act normally (output RF when keyed) while just keying it doesn't. Without touching any of these, when keyed the radio goes thru all the motions you would expect, display changes to TX, meter from S to F or R, a sidetone is generated if in CW, etc. but no RF is produced by the final amplifier unless being "probed". Any suggestions I could try to fix this problem?
Another problem that has plagued me forever is the radio will sometimes lock up and the display "wig out" when tuning very slowly or moving the tuning knob back and forth seems to bring this problem on. The RIT encoder (same unit as listed in the BOM) seems rock solid and maybe it is because I have some .01 uf caps across it. I am using a CUI INC C14 optical encoder for the tuning and this requires some pull up resistors. Do you think putting some caps across this encoder might eliminate the problem?
Thanks for your help and suggestions. I'm slowly "getting there",

Author:  ecpilot [ Sat Jan 26, 2013 5:26 pm ]
Post subject:  Re: Getting There

Another thing I forgot to mention Jim is I can't seem to adjust the output level either with VR1 or the Hi/LO switch on the front panel. It seems to be around 20 - 30 watts all the time and if anything a little higher when the front panel switch is set to 6 Watts. Very strange.

Author:  ecpilot [ Sun Jan 27, 2013 4:49 pm ]
Post subject:  Re: Getting There

I tried a couple of .01 uf caps on the tuning encoder and that seemed to fix the the problem of the radio locking up and the display going nuts when tuning slowly. So that is one less problem to sort out. :D I still haven't figured out the quirk with the final amp not working without some"probing assistance". Still trying to figure that one out.

Author:  ecpilot [ Sun Jan 27, 2013 5:00 pm ]
Post subject:  Re: Getting There

I spoke too soon on the tuning problem going away. It just did it twice in a matter of a minute so that still looks like an open item. Sometimes a key press will have the same result, either the radio will lock, display will turn to garbage, or the radio will actually reset. It doesn't happen often but it has occurred.

Author:  ecpilot [ Fri Feb 01, 2013 4:29 pm ]
Post subject:  Re: Getting There

Well Jim I seem to be taking some steps backward here as now I can't get the final amp to generate any RF even with "probing" like I could previously. I have been reading the "trouble" thread and most of my readings are similar to the ones you have posted. Here is a rundown of what I have:
Measurements made 28.310Mhz mode = CW
U2, Pin 1 840mv RMS, 2.4V pk-pk
U2, Pin 7, 295mv RMS, 880mv pk-pk
U5, Pin 1, 45mv RMS, 140mv pk-pk, VR1 max clockwise
U5, pin 4, 170mv RMS, 740mv pk-pk, varying waveform
U5, pin 5, 310mv RMS, 1.3V pk-pk, varying waveform
U5, pin 6, 200mv RMS, 620mv pk-pk varying waveform
U5, Pin 7, 200mv RMS, 620mv pk-pk varying waveform
C104 and C58, 750mv pk-pk and waveforms look the same
LO, O1, pin 4, 290mv RMS, 730mv pk-pk AC coupling 1V RMS, DC coupling
MX1, pin 8, 113mv RMS, 305mv pk-pk (receive mode) 100mv RMS, 290mv pk-pk (Xmit)
MX1, Pins 3 and 4, 225mv, RMS, 375mv pk-pk
MX1, Pin1, 54mv RMS, 210mv pk-pk
At L3 I get 22mv RMS and about 80mv pk-pk and then maybe 5mv or so going into L2.
Basically the same kind of deal with L5, L6 and L7.
I don't get anything to speak of coming out of the filters to C45 or C49. Going by memory what I believe I measure previously on C45 and C49 was like 500mv and now I am getting virtually nothing. I seem to be spinning my wheels now at this point and have looked at this a number of times and am thinking it might be time to put it up for awhile. Any ideas you might have would be most welcome.

Author:  jimveatch [ Sat Feb 02, 2013 12:22 am ]
Post subject:  Re: Getting There

I may need to power mine up again and see what I get, things seem mostly normal up to the mixer. The LO seems a bit low, should be +7 dBm which is about 500 mV RMS and the conversion loss should be less than 6 dB (1/2 the voltage). The band filters seem to be not working correctly which, if they aren't terminating the mixer properly could be part of the problem.

You mention voltages but can you tell that these signals are on or close to the frequency that we expect them to be?


Author:  ecpilot [ Sat Feb 02, 2013 10:26 am ]
Post subject:  Re: Getting There

I have a bigger problem now as I tried to fine tune the frequency for 6M (it was just a hair low) I connected the PICkit3 programmer to the radio and I get an error "Target Device ID (00000000) does not match expected Device ID (00005500). I tried to program a change and now of course the radio is dead. I have no idea why I am getting this error as the device that is selected is a PICF18F45K22 and the programmer selected is a PICkit3. I didn't have this problem before obviously when I was making frequency corrections. Hopefully I can figure this out. To answer your other question about the expected frequencies for the measurements I gave you, I believe they are correct. The LO was in the 38.6MHZ range, the pins on U2 were 16Khz. I will try to get you more specific information once I breath life into his now dead radio.
Thanks for your help,

Author:  ecpilot [ Sat Feb 02, 2013 12:12 pm ]
Post subject:  Re: Getting There

Wheew, found and corrected that problem. The caps I had put on the encoder were causing the problem. Radio is back alive and doing well and now right on Frequency on 6M. I adapted an old hand mic from a Ranger marine radio and now on SSB I could get the frequency dialed in exactly so that it sounds natural on all 3 bands. Now back to the final amplifer issue.

Author:  ecpilot [ Sat Feb 02, 2013 1:22 pm ]
Post subject:  Re: Getting There

I was thinking that the mixer must be bad but the output is close to what I would expect although lower in amplitude. With the transceiver frequency set at 25.000 MHZ, I am measuring 35.7 on Pin 8 (LO), 10.7 MHZ on pins 3 & 4 (IF) but the output is 25.18 MHZ. Lifting the RG174 from J17 allows me to measure 25.04MHZ at C45 and it has an amplitude of 7mv RMS and about 30mv pk-pk but it is a pretty ratty looking waveform. Maybe I should try a new SI570? The output is less then 300mv and you are saying it should be around 500mv.

Author:  ecpilot [ Sat Feb 02, 2013 2:08 pm ]
Post subject:  Re: Getting There

Thinking back I ordered the LVDS version of the SI570 vs the CMOS version because the CMOS version was out of stock. At the time I thought the only difference was the LVDS version had a little tighter frequency tolerance (20 ppm vs 50 ppm) but it might have a different output level too I guess. My device is marked BBC000141G on the top so I will order the correct CMOS part.

Page 1 of 2 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group