Sunday, January 24, 2021

New Toy: HP 8656B Signal Generator

 


It was time to upgrade my repair bench with a new piece of equipment. I bought this HP 8656B (w/ Opt. 001) to replace my HP 8640 and Heathkit SG-8 for customer repairs. This is a very nice signal generator and easier to use than my older models. I placed it under my spectrum analyzer since both units are used to adjust radios for optimum performance.

If you have a shortwave radio or ham radio that you would like repaired, then please send me a message.

 

 

 

73,

JJ W9JES

Vizio M50-C1 Smart TV Repair

 



One of the other projects over the holiday's I managed to fix is my Vizio M50-C1 smart TV. This TV is one of the early 4K models introduced in 2015. The TV has been great and is on for 15 hours a day on average. It was used for playing games and watching shows/movies.

One day, it stopped working and wouldn't power on. My immediate thoughts were bad capacitors in the power supply since I've repaired several flat screen TVs with similar issues. 

China doesn't offer schematics for this model so troubleshooting had to be performed the traditional way. The Vizio M series TVs from this era all used a similar, modular board design where each major function was contained to a separate board. For example, there is a power supply board, a scaler board (GPU, sound processor, and inputs), inverter board and T-Conn board.

Fortunately, the power supply was fine after checking all voltages and signalling. I noticed the scaler board had a bi-color LED and would turn purple when a power on sequence occured and turn red when the TV was off.

I figured that the board must have a fault, but wanted to rule out the inverter and T-Conn boards. I disconnected the inverter board from the scaler board and applied ground to a SCR (Silicon-controlled Rectifier) input on the board. I was able to see the backlight turn on, but no picture. At least the backlight and inverter board were working to some degree.

I disconnected the T-Conn board and ran some tests. It seemed to be working fine and would only affect how the picture was displayed on the screen. If it were faulty, then I would see only part of the screen or solid colors.

I removed the board and saw this when I flipped it over. Nasty flux corrosion on the board! Talk about subpar garbage coming out of the Chinese factory.

 I moved on to the scaler board as the culprit and headed over to the Badcaps forum for assistance. I quickly learned that this model along with the others from 43" up to 75" had similar issues. The main cause is cracked solder joints on the BGA chips under the heatsink.This occurs over time from power cycling the TV causing expansion/contraction from hot to cold. I attribute this to poor engineering, poor design, and shoddy assembly more than typical wear and tear.

My options were to either buy a replacement scaler board, send the board out for repair, reball the BGA's with a rework station myself, or try an experimental heat gun reflow.

I looked around for a replacement scaler board and came up empty handed. Unless I wanted to spend upwards of $200 for a board (1/3 cost of the TV). I opted to try the heat gun reflow approach.

The design of this board and massive heatsink made it very challenging to perform a heatgun reflow.

 

I ended up using a temperature probe and Harbor Freight heat gun to perform the reflow. I preheated the board from the back side and brought it up to 230 F over several minutes. Then I increased the temperature to about 400 F and heated the board evenly paying special attention to the BGA chip area. I kept the board at this temperature for about 15 minutes to reflow the solder balls, then let it slowly cool down to about 120 F. 

I let the board sit for 1/2 hour and place it back in the TV. It powered up and worked! The TV has about 80 hours of "TV time" without any issues.

Please note this is most likely a temporary fix and not a replacement for a proper reball of the BGA chips. I added some 40mm brushless fans to the heatsink and cut holes on the TV cover to reduce the 200+ F temps down to 160 F while using the TV.

If you have similar issues, please head over to the Badcaps forum for assistance. You can also watch this video for performing a heatgun reflow yourself. If you want your board professionally repaired, then I suggest Nick's TV service.



73,

JJ W9JES


Tektronics 465B 100MHz Oscilloscope Repair

 



 

I previously mentioned that my old analog scope needed repair. I use this 465B on a regular basis to diagnose and repair electronics and was disheartened to see it failing. All radio projects came to a halt as I had to bring the trusty 465B into the operating room for revival.

 

Symptoms

The scope was operating normally until I was using it to diagnose a TV board. The front panel lights would turn off and back on at random times. The CRT would also blank out when this occurred. Turning the scope off and on would sometimes remedy the situation for 5 to 20 minutes until it completely died.


Diagnosis

I removed the covers and measured voltages at the test points indicated in the manual. All voltages were correct +/- 1% except for the 5 volt rail. My initial thoughts were the old rectifier capacitors were shorted. I tested the capacitor in circuit and it wasn't shorted so I moved on to the bridge rectifier (CR1551). I measured 55 volts DC as expected.


Next, I moved on to Q1556 (MPS-U45). This transistor appeared to have a solder blob shorting the base and collector pins. No idea how that happened unless another component got hot? I removed the transistor and tested with my LCR meter. It tested as resistor. I ordered a new transistor and installed it. Tested for 5V and still no voltage present.

 


 

I removed one leg of R1559 to see if there was a short to ground from Q1556 or Q1558. Nothing appeared to be shorted.

I measured voltages of the pins on the U1554A IC chip (MC1458 Dual Op Amp) and noticed pin 3 had no voltage. It should be 5 volts. Pin 8 was fine at 15 volts and pin 4 was fine at -8 volts. Pin 1 measured at less than 1 volt (it should be approx 6.7 volts).

 

Repair

The MC1458 Op amp was internally shorted. I ordered a replacement at Mouser p/n 595-MC1458P and installed it. The scope came to life and is working great!

 


 

73,

JJ W9JES

Icom 728 PLL-VCO Repair

 


 

Hello Radio Friends.

I had an opportunity to pick up an Icom IC-728 transceiver over the holidays. I used to own the this model years ago before trading up for a Kenwood TS-2000. The 728 was a fun and simple to use radio and got me deeper into enjoying HF communications.

Initially, I offered to repair this radio for a fellow ham, but he decided to sell it to me at a great price instead (I guess his Icom 7600 meets his needs, haha!).

The 728 is a basic HF transceiver covering all HF bands/modes and general receive with up to 100 watts output. It utilizes a triple conversion receiver and selectable band pass filtering. This radio does not include a built-in antenna tuner and most of the functions are accessible on the front panel buttons to simplify the deep menu driven learning curve of modern gear. The IC-728 came to the market in 1992.

I met the local ham who said this radio was owned by a silent key and he obtained it in its current condition. Everything worked as it should except no TX/RX on 8MHz to 15 MHz. No receive or transmit on 20-30 meters. The ham suspected faulty BPF circuitry.

 I brought the radio home and started to look it over. Examining the schematic, I noticed the filter board is embedded deep inside the rig. Suspecting a bad coil or relay; I removed the top and bottom covers and dug in. I checked the relays and voltages to each filter stage and everything was in spec.




 
 

 I worked my way backwards and checked the VCO section. Bingo! This radio splits the VCO into 4 sub circuits which activate their respective band pass and low pass filters.



I checked the voltages on each VCO and found #2 out of spec at 4 volts. I adjusted trimmer cap C46 and brought it back to 7 volts. The radio started working again between 8 and 14 MHz.

Reading a bit on these rigs, I discovered that the trimmer caps are notorious for going bad or out of spec over time. The proper way to fix this issue is to replace the capacitors with new ceramic ones.

I ordered some caps from Digikey and replaced all four of them. Here are the part numbers and values in case you run into the same issue.

VCO1 0.5-7.99999  C35 Trimmer Cap #4610001130  CVSSA1001  10pf
VCO2 8.0-14.99999 C46 Trimmer Cap #4610001130  CVSSA1001  10pf
VCO3 15.0-21.99999 C59 Trimmer Cap #4610001000  CVSSA0701  7pf
VCO4 22.0-30.0 C70 Trimmer Cap #4610001000  CVSSA0701  7pf




73,

JJ W9JES




Monday, December 21, 2020

SDR Showdown $25 VS $120

Hello radio enthusiasts. Many of you know of or have heard of Software Defined Radios (SDRs) especially if you read my blog. Well, I recently purchased another SDR to add to my gear. I wanted to try out one of the higher end SDRs on the market and see how they stack up against the RTL-SDR Blog V3

I looked at reviews, videos, demos, and feature comparisons of SDRs in the $100-160 range and narrowed it down to two devices. The SDRplay RSP1A and AirSpy HF+ were top contenders in this price range based on features and performance. Black Friday sales significantly brought the price range of these devices very close together. There seems to be a lot more reviews for SDRplay products so I ended up buying the RSP1A.

Here is my comparison between the RSP1A and RTL-SDR Blog V3.



 

Prep and Equipment

I used a 25 foot, indoor, longwire antenna with 3 feet of RG314 coax terminated to a SMA female connector. This antenna was connected to a SMA Tee so I could run the RSP1A and V3 simultaneously on the same Windows PC. Frequencies used were in the HF band in the early evening and late afternoon. SFI was about 85 during the tests.

Contender 1: SDRplay RSP1A ($120 USD) The RSP1A boasts a 14 bit ADC with up to 10MHz bandwidth, simultaneous connections, and selectable notch filters (AM/FM/DAB) using SDRuno software. It's frequency coverage is 1KHz to 2GHz. Installation of the drivers and SDRuno software were really easy. I had the RSP1A up and running in about 15 minutes. Datasheet link here.

Contender 2: RTL-SDR Blog V3 ($25) The RTL-SDR Blog V3 uses a 8 bit ADC with up to 2.4MHz bandwidth. There are no onboard filters for AM/FM/DAB. Frequency coverage is 500 KHz to 1.766 GHz. Driver installation and software installation were not quite as smooth as SDRplay, but it wasn't too bad with the excellent tutorials online. Datasheet link here.

The RSP1A was used with SDRuno and the V3 was used with HDSDR. Using the RTL-SDR Blog V3 with SDRuno is clunky at best with the EXT-IO driver installation.

Both units were configured with medium AGC and full use of the internal RF amplification available in the software settings. Both devices were calibrated to WWV and matched for DB/Signal levels with a other hardware on the same antenna connection (Tecsun PL-880 and Icom-751a).

 

 

Construction





Comparison

The RSP1A displayed  8 MHz bandwidth. It was refreshing to see more range above and below the LO. You may ask why only 8 MHz displayed instead of 10 MHz? It can display up to 10 MHz in some cases, but I am not sure why I was only seeing an 8 MHz spread. I did not see or hear many signals coming through the noise floor. I did not hear any DX stations while tuning the SDR.

The V3 displayed 2.4Mhz bandwidth and I saw more stations coming through the noise floor on this SDR. I was able to tune and listen to a few stations easily.

I was a bit puzzled by the RSP1A and reduced the bandwidth down to 3 Mhz bandwidth for better comparison. I was able to see and listen to some of the same stations as the RTL-SDR Blog V3 now. I could hear DX stations on both devices, but the audio was more intelligible on the V3. This is where things became more comparable between the devices and performance was similar.

The RSP1A had better sensitivity at 3 MHz than 8 MHz bandwidth. The RSP1A had problems pulling out intelligible signals in or near the noise floor. I was hoping for a more sensitive SDR with a wider frequency display using the RSP1A, but that was not the case.

Another observation was the audible noise between the two devices. It seemed the RSP1A had more noise on the signal than the V3. I found some information on SDRplay's forum from others who experienced the same issue. I did not find a good technical response or resolution to the issue.

Another notable feature between the RSP1A and the V3 is the onboard filtering. The RSP1A shines in this area because SDRuno automatically selects the appropriate filters to reduce overloading and interference while tuning. The filters work extremely well as I did not have AM/FM bleed-over on HF. External filters and add-on boards are available for the RTL-SDR BlogV3 to rival the RSP1A's built in features. AM bleed-over to HF bands is a problem with the V3 due to lack of selectable filters.

The RSP1A is housed in a plastic box with some "metallic" spray covering the inside. This is an attempt to reduce EMI and RFI. It did not perform well when I moved a laptop power brick near it as I saw numerous spurious signals on the bandscope.

The RSP1A requires a separate purchase of a shielded USB A/B cable. Those will cost between $7 and $10. Why it's not include with the product baffles me. If you want further EMI and RFI shielding, then you can purchase a metal case for $25 from third party sellers.

The RTL-SDR Blog V3 is housed in a metal case grounded to SMA jack. It also has USB filtering to reject interference. My laptop power brick had little effect on the SDR displaying only a couple spikes on the bandscope. There is no need to purchase a separate USB cable for typical installations.

The RSP1A appears to lack heat dissipation as there are no heatsinks on the processor or other components. I don't know if it is needed and did not notice any substantial drift or performance issues during the test.

The RTL-SDR Blog V3 uses the metal case as a heatsink to keep the processor stable with some non-conductive thermal tape for heat transfer. The metal housing does get warm, but I did not notice substantial drift after hours of use.

 

 

Conclusion

The RSP1A and RTL-SDR Blog V3 seem similar from a performance standpoint. Is the RSP1A worth the 4x price tag of a V3? That is an absolute NO from me!. There are several reviews for this RSP1A from other HAMs and SWLers praising this SDR for HF listening. I don't see what all the praise is about. I do understand the out-of-box experience is a little better with the RSP1A, but that doesn't seem to be enough reason to buy it. The V3 is rather simple to setup with ZADIG and the appropriate driver. Using Direct sampling of the V3 produced rather impressive results too.

The SDRuno software interface is not as user-friendly as it could be. It offers an extensive array of settings for the tinkering mind to spend hours tweaking and fiddling which is great. I found the workspaces thing to be a pain in the butt. I did not like the taskbar littered with several open windows. New versions are coming out frequently to address the numerous bugs in the software so I am happy to see an active development community for their product.

HDSDR is a very simple out-of-box installation as well. It just works with only minor tinkering. It is more user friendly than SDRuno for a new or casual user.

I tested both devices using SDRuno and HDSDR software. The performance of both SDRs was about the same. Keep in mind that using the RSP1A or RTL-SDR Blog V3 outside their native software offerings will require an EXT-IO driver that may reduce functionality.

I regret buying the RSP1A and should have tried another offering like the Airspy HF+. Maybe another review in the future?

 

 

 

73,

JJ W9JES

Thursday, December 10, 2020

A Litte Update

Hello folks!

I wanted to share a little update with you. I am still working on projects and have a few radios in for repair. Most of it came to a halt as my beloved Tektronix 465 scope is on the fritz. I had to change focus to repairing the scope (5V power rail had a short) and waiting for parts. I also picked up another NanoVNA to have some fun with. This VNA will be used with custom firmware and see if we can make some interesting projects out of it. Also got to experiment with a SDRplay RSP1A. You will see a review soon.


 

I have a couple shortwave receivers here to repair and an Icom transceiver. I will try to share some updates as time permits over the holidays.

Speaking of the holidays; our radio club held the annual Christmas party tonight. It was a bit different than previous years due to Rona and was hosted over a virtual video conference. It was fun nonetheless.

Happy Holidays and I will see you soon. Let's hope for more 100+ SFI days to enjoy DX'ing!


73,

JJ W9JES

Saturday, November 28, 2020

Ham Radio Movies

 Who remembers this movie? This is WM1ATE calling HB9RFX. 

High Frequency (1998)

Of course, many of you also remember the movie, Frequency (2000) and a subsequent TV series.

What other shortwave or ham radio movies do you remember?

 

Here is a list compiled by Dave, AD7DB.

"Gone With the Wind" - 1939. Drama. The classic story of Brett and Charlotte as they try to save their 100 foot tower in the worst windstorm to hit Georgia since the Civil War.

"The Longest Yard" - 1974. Comedy. Burt Reynolds acquires the largest property in a new subdivision, then finds his plans to put up a huge antenna farm thwarted by a hostile homeowners association (Jackie Gleason, Loni Anderson, Dom DeLouise).

"The Lost Contest Weekend" - 1945. Drama. Ray Milland in a dramatic battle on 20 Meters for one elusive QSL.

"I Was a Teenage Novice" - 1957. Drama. A troubled teenager (Michael Landon) finds fun and excitement after getting a ham license.

"It Came from Radio Shack" - 1977. Horror. Bill Bixby tries to keep a computer called TRS-80 from taking over the world.

"Rear Window" - 1954. Suspense. Alfred Hitchcock did several marvelous films heavy on the subject of ham radio. In this movie, James Stewart plays a man confined to a wheelchair, determined to break the CC&R's and put up an end-fed wire antenna going out his apartment window - without the neighbors catching on. Grace Kelly and Thelma Ritter also star. Watch for Hitchcock's appearance over in Ross Bagdasarian's apartment.

"The Man Who Knew Too Much" - 1956. Suspense. James Stewart shows up at an FCC testing office for his ham license. What he doesn't know is, he's over-studied for it, and is smarter than the examiners, who force him into working for them! Watch for Hitchcock's appearance as someone taking a code test! See if you can figure out what he's sending!

"The Birds" - 1963. Thriller. The classic about a bunch of people stranded in a Northern California town who find that the only means of communication to the outside is by way of some of them newfangled OSCAR satellites.

Other Nominees:

"Frequency" - 2000. Drama. Ham operator finds his radio can time warp and talk to his dad decades in the past. How does he expect to QSL?

"Contact" - 1997. Drama. Female ham operator (Jodie Foster) controls the Arecibo radiotelescope, where she picks up an extraterrestrial signal. Now that's what I call DX