View Full Version : Another Motorola VK-106 restoration attempt


pdr-fml
11-24-2016, 02:55 PM
Happy Thanksgiving everybody. I am in process of trying to restore a 1948 Motorola VK-106 that i had found at estate sell. I have never done this before so I am on the learning curve soaking in information when I can. Mine is very similar to the one Banderson posted a few weeks ago so I wont include too many pics. When I got the set I did not know anything about the current condition whether or not tubes were all there or CRT any good. Well so far things have turned out pretty well and have not run into any project stopper problems so far I think. I do have a problem I would like to get an opinion on and I will detail this a few post down but first just a few pics of project and what I have done so far -see posts below.

Here is pic of set the day I got it and by the way I paid 50 and not 100 so not exactly a bargin.

pdr-fml
11-24-2016, 03:00 PM
Here are some more pics of set. All tubes were there except for HV rectifier tube and one tube was wrong type.

pdr-fml
11-24-2016, 03:23 PM
I have been busy last few weeks with this whole thing just hoping that CRT was going to come to life. My hopes were up because i found some problems that may have been reason for shelving the set that were not CRT related. Two burned up resistors and a blown fuse so I kept thinking CRT may be okay. By the way I did check crt filament and tube filaments and none were open. I restuffed two can caps and relocated two to inside chassis bottom.

pdr-fml
11-24-2016, 03:43 PM
After recap job and replacing few resistors I cranked her up saw a flame up down below in chassis. Turned out to be a tapped power resistor that had one bad section that I had bypassed with new dale screw down power resistor but was still shorting out. Ended up replacing whole thing. I do have variac and was gentle with set at first. All tubes were glowing and static from speaker (no signal attached just looking for raster) but nothing at all on tube. adjusted ion trap all over the place and nothing at all. Also appeared to have high voltage using screwdriver arc test. Pulled all tubes out and let crt filament glow for a couple hours. Still nothing. I looked at voltages at crt neck and looked at schematic for orgins of voltages and started doing a little trouble shooting and pulled 12au7 video output tube. Had put everything back to normal and powered back up and still nothing. Decided to adjust ion trap again and finally got a raster. I got a replacement tube from a source and reinstalled. I am not a 100% percent about tube being problem but am going to test one day. I was really getting discouraged but now very hopeful.

Current problem I am trying to solve is shown in pic below. I got a old tv repair book and for the white vertical strip problem I am seeing as shown the book suggest either damping tube or bad deflection yoke. What do you guys think?

Kevin Kuehn
11-24-2016, 05:58 PM
Very nice job on replacing those caps and resistors! :thmbsp: I'd agree the damper tube is generally responsible for those type defects on the left side of the picture. First thing I'd try is replacing the damper tube, possibly try a few. Adjusting the horizontal drive control could also have some effect.

decojoe67
11-24-2016, 08:41 PM
Great job. I think you got a great bargain with that set. Those Motorola's a fairly uncommon and a classic '40's console. The CRT alone would cost at least $50.
Enjoy it!

pdr-fml
11-25-2016, 09:35 AM
Very nice job on replacing those caps and resistors! :thmbsp: I'd agree the damper tube is generally responsible for those type defects on the left side of the picture. First thing I'd try is replacing the damper tube, possibly try a few. Adjusting the horizontal drive control could also have some effect.

Thanks for the advice. Well I am fresh out of damper tubes -calls for a 5v4g so I guess I will place an order might get two just in case. I will try the drive control before I do that and see what happens.

pdr-fml
11-25-2016, 09:39 AM
Great job. I think you got a great bargain with that set. Those Motorola's a fairly uncommon and a classic '40's console. The CRT alone would cost at least $50.
Enjoy it!

Thanks. I guess I lucked out on the 10bp4 not being a dud. Have not tested it but it seems bright enough. Just to add the crt appears to be a rebuild to me due to the neck having a cut line around it.

kvflyer
11-25-2016, 10:39 AM
Looking good and you are certainly on track for a complete restoration. The 5V4 could be a 5V4GA also if that is easier to find and I guess you got a HV rectifier since you have a raster.

Nice job, keep the pictures coming.

Kevin Kuehn
11-25-2016, 10:44 AM
You can use a 5V4GA in place of the G. The audio guys covet those G style for their more curvy sound. ;)

pdr-fml
12-04-2016, 05:09 PM
Very nice job on replacing those caps and resistors! :thmbsp: I'd agree the damper tube is generally responsible for those type defects on the left side of the picture. First thing I'd try is replacing the damper tube, possibly try a few. Adjusting the horizontal drive control could also have some effect.

Ok. I got rid of the white vertical lines by adjusting the horizontal drive control. When I went to adjust I found that trimmer screw was completely missing. Stole screw from another from trimmer in tuner for channel that will not be used. Unfortunately I have other problems with set and have decided that I need to test all tubes before I go any further. I know someone at work that has a tester and will try to get this done shortly.

pdr-fml
03-13-2018, 05:48 PM
It has been over a year since my last post about my motorola vk106 and I have been working on it every now and then but still have issues with it but I am determined to get this thing working. I was just wondering if anyone has actually seen one of these up and running properly or are they all just works in progress like mine is? I guess this would include the VT105 and VT107 which have similar chassis.

decojoe67
03-13-2018, 08:34 PM
It has been over a year since my last post about my motorola vk106 and I have been working on it every now and then but still have issues with it but I am determined to get this thing working. I was just wondering if anyone has actually seen one of these up and running properly or are they all just works in progress like mine is? I guess this would include the VT105 and VT107 which have similar chassis.
A long-time repairman friend of mine has that model in storage and I've hinted at acquiring it for many years now. He never seems to care about parting with it. I believe he mentioned that those are good players once restored. Here is the only example of that chassis that I've ever seen working. It's the tabletop VT-105 version: https://www.youtube.com/watch?v=MvVt7lppTKQ
I had the chance to get one of those locally years ago. Should've of went for it! Those 10" '48 Motorola's are uncommon.

Eric H
03-13-2018, 09:46 PM
. I was just wondering if anyone has actually seen one of these up and running properly or are they all just works in progress like mine is?

I have a 105 that I restored and it has a beautiful sharp picture. I haven't run it in a while though.

I nearly forgot I have a (crappy) video of it on YT.
https://www.youtube.com/watch?v=MvVt7lppTKQ

Phil Nelson
03-13-2018, 09:56 PM
still have issues with it but I am determined to get this thing working.What are those remaining issues? Seems like you must be getting close . . . .

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

pdr-fml
03-14-2018, 07:49 PM
What are those remaining issues? Seems like you must be getting close . . . .

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

I guess my main problem is that the set has virtually no reception when I hook my digital convertor box up to it. It has actually gotten worse from what it was last time i checked it which was many months ago. I was getting a very faint picture with audio every now and then but now it is next to nothing. Right now I am going to go thru the tedious task of verifying component location and values which is probably a good idea since I did a major recap job shortly after getting the set. I think my tubes are good and I have checked them on a tester. I may be asking you guys about the best way of injecting video from convertor box into the video circuit to try to isolate problem better.

Electronic M
03-14-2018, 09:27 PM
Have you confirmed the DTV box RF signal quality with a different analog TV? Some cheap RF modulators (like those built into most home video sources) suck. Have you tried the set with a different modulator?...Sometimes a set happens to not like a specific modulator despite the modulator working with other sets...RF can behave like black majick sometimes.

Have you cleaned the tuner contacts, and tested the tubes in the tuner and IF? If the set has AGC have you adjusted it and verified it's operation? Is the internal tuner balun (usually mounted outside or inside the tuner box and linking the ant lead to the first tuner tube) still good?....Lightning killed a lot of tuner baluns back in the day.

Do you have a B&K 1075/76/77 series analyst? Those can modulate and inject IF carrier into the IF strip. Doing test injection with such a tool can id dead tuners and IF stages.

Have you compared socket voltages in the tuner and IF to those listed in the service literature?...If a stage has a major defect it should show up in the voltages.

These are all the easy steps to fix it or get you chasing a likely source of the problem....Beyond this lies the dark art of alignment, and or the engineering art of video injection.

pdr-fml
03-14-2018, 10:25 PM
Have you confirmed the DTV box RF signal quality with a different analog TV? Some cheap RF modulators (like those built into most home video sources) suck. Have you tried the set with a different modulator?...

Yes I did verify its operation with with my old Panasonic "flat screen" crt set I keep up in the attic now.

I just found two problems tonight while verifying actual wiring with the schematics. One problem is what looked like a small solder bridge not real sure though and the big one is I hooked up a resistor wrong that I replaced when I did cap job. The resistor was supposed to be feeding a cathode of Horiz osc/control tube off the B- supply and instead of going to B- I had it hooked up to the opposite grid on same tube. NO wonder the horizontal has always acted crazy.
I will try to repair tomorrow and check more things. Thanks for the advice.

pdr-fml
03-31-2018, 06:00 PM
Yes I did verify its operation with with my old Panasonic "flat screen" crt set I keep up in the attic now.

I just found two problems tonight while verifying actual wiring with the schematics. One problem is what looked like a small solder bridge not real sure though and the big one is I hooked up a resistor wrong that I replaced when I did cap job. The resistor was supposed to be feeding a cathode of Horiz osc/control tube off the B- supply and instead of going to B- I had it hooked up to the opposite grid on same tube. NO wonder the horizontal has always acted crazy.
I will try to repair tomorrow and check more things. Thanks for the advice.

What I mentioned above turned out to be wrong the resistor was in correct location. In fact I have verified the proper connection of every single component and did not find anything connected wrong.

I have a few questions. I have included pic of my converter box. It is a Apex model DT250A. Does any one have any experience with this box working or not working with older set? My other question is can I feed the coax rf output (channel 3 or 4) from this box into the RF converter/mixer grid and expect a good signal or is it too weak. This would be bypassing the RF amp tuner stage where I think I may have a problem. I have successfully injected a 21.9MHz (audio IF for my set) FM modulated signal from my signal generator into the grid of the mixer and did alignment on sound IF (atleast I think I did - everything sounded good afterward). After I did the sound alignment my next check was going to be to see if I could get good audio using converter box. Well it did not work. All I got was buzzing noises. I am going to reverify my signal gen output accuracy but I think it is dead on it is a HP synthesized model. I even jacked around with the local osc adjustment for channel 3 and all I got was several FM radio stations coming thru nicely. I tried viewing signal with oscilloscope and never found anything that looked like video signal. So am I going to have to go thru tuner and RF amp?

Kevin Kuehn
04-01-2018, 12:39 PM
My other question is can I feed the coax rf output (channel 3 or 4) from this box into the RF converter/mixer grid and expect a good signal or is it too weak. This would be bypassing the RF amp tuner stage where I think I may have a problem.

You can not run the rf channel 3 or 4 directly though the mixer because it will not provide the needed IF frequency. The correct IF frequency is generated by the rf channel frequency beating with the receivers local oscillator freq. See below for more info.

I have successfully injected a 21.9MHz (audio IF for my set) FM modulated signal from my signal generator into the grid of the mixer and did alignment on sound IF (atleast I think I did - everything sounded good afterward). After I did the sound alignment my next check was going to be to see if I could get good audio using converter box. Well it did not work. All I got was buzzing noises. I am going to reverify my signal gen output accuracy but I think it is dead on it is a HP synthesized model. I even jacked around with the local osc adjustment for channel 3 and all I got was several FM radio stations coming thru nicely. I tried viewing signal with oscilloscope and never found anything that looked like video signal. So am I going to have to go thru tuner and RF amp?

You can set your generator to the video IF frequency and check the mixer and IF stages, similar to how you did the sound IF alignment. Just make sure you have the channel set to a blank position between 2 and 13, to disable the local oscillator. You may also use your signal generator as a video test bar generator by AM modulating the IF frequency with 1200hz. If 1200hz is not possible it's OK to use 400 or 1000hz. 1200hz in theory will give you 20 horizontal test bars on the CRT screen. The AM modulation beats with the receivers vertical sync oscillator and provides black and white test bars on the CRT screen. Normally you would start at the Video IF closest to the detector and work your way back towards the antenna input. You can even set the frequency generator to any channels video carrier(61.25mhz for ch 3) and connect it to the antenna input(same AM modulation will produce bar pattern). In this instance you do need to tune in the channel so that the local oscillator will beat with the video carrier freq and produce the correct IF.

It's always a good idea to use a coupling cap in series with you generator output just in case you accidentally hook into some high voltage source. Generally you'll be feeding the signal into the the grid of each stage.

Phil Nelson
04-01-2018, 05:41 PM
I even jacked around with the local osc adjustment for channel 3 and all I got was several FM radio stations coming thru nicely.The FM radio band is located between channels 6 and 7. If you turned the channel 3 oscillator to receive FM radio, that's pretty far off (i.e., somewhere between channels 6 and 7) from where you want it to be.

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

pdr-fml
04-01-2018, 10:27 PM
You can not run the rf channel 3 or 4 directly though the mixer because it will not provide the needed IF frequency. The correct IF frequency is generated by the rf channel frequency beating with the receivers local oscillator freq. See below for more info.

When I aligned the sound IF I did as you said and turned tuner to blank position like the instructions say to do in the manual. When I hooked convertor box to mixer grid I then set the tuner to channel 3. Wouldn't this enable the local osc? You gave some great ideas for testing video IF. My signal generator I got should be able to do this no problem. I discovered though it is quite limited for sweeping functions. I disabled all the high voltage and removed the crt for what I am doing right now so I will try that later when I reconnect everything. I did verify my signal generator accuracy by using my Sony multiband radio using the SW band and tuning in to generator.

pdr-fml
04-01-2018, 10:39 PM
The FM radio band is located between channels 6 and 7. If you turned the channel 3 oscillator to receive FM radio, that's pretty far off (i.e., somewhere between channels 6 and 7) from where you want it to be.

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

This was only after I started to adjust it thru its limits just to see what would happen. I eventually got it back roughly to where it was originally. I guess the fact that I was able to tune to anything tells me the local osc is working. I am thinking my video signal was not strong enough to pick up the audio channel but then how is that not strong enough yet I am pulling in FM radio stations off the air? I will get it figured out one of these days hopefully before I break something. I sure do appreciate the advice I get from you guys.

Kevin Kuehn
04-02-2018, 09:46 AM
When I aligned the sound IF I did as you said and turned tuner to blank position like the instructions say to do in the manual. When I hooked convertor box to mixer grid I then set the tuner to channel 3. Wouldn't this enable the local osc?

The problem is that the local oscillator can't generate it's proper frequency when you inject your channel 3 rf directly into the grid of the mixer(see below edit). If you feel your rf amplifier is the defective stage, then I would suggest you make voltage and resistance checks around that area per the SAMs info. I'd like to point out that starting at the antenna end is sort of working the problem backwards, as it creates a lot of unnecessary confusion. The logical way to troubleshoot these things is to inject a signal as close to the output stage as possible. Once you have a picture or sound, you work your way back through the stages towards the antenna input. When you lose the signal, it's at that point that you have found the problem area.

[edit] After looking at your sets tuner circuit more thoroughly, I believe your injecting the rf channel 3 or 4 directly into the mixer grid will load down the oscillator signal feeding that same point through the 1.5 pf cap. I believe you would need some type of isolation or impedance matching circuit between your signal generator and the grid of the mixer. Even then I think without the gain provided by the rf amp, it would not mix correctly with the oscillator, or at best it would provide a greatly reduced amplitude IF signal. Keep in mind that your HP generator likely has a 50 ohm output impedance.

It would be great if one of the EE engineering types hanging around here could explain these type circuits so that everyone(myself included) could better understand their operation. ;) I only know from experience that injecting an rf signal at a critical mixing point tends to load down the circuit and create errors.

pdr-fml
04-03-2018, 04:56 PM
I think after I check a few more things I am going to look over my antenna input section real good to make sure there is no damage there. Someone said it is possible it could have been damaged by lightning which makes sense. If I can give that section a thumbs up then I will hook my converter box to antenna input and not have to worry about injecting into mixer.
On a side note I just noticed locally on Craigslist someone if trying to sell a Motorola VT 107 which has same or nearly same chassis as the one I'm working on right now. According to the ad it has been in storge since the 60s. They are asking too much right now but I will grab it if the price is right. I guess I've got the bug.

pdr-fml
04-10-2018, 09:51 PM
Have made some pretty good progress last few days with my VK-106. My reception problem looks like it was due to a bad antenna lead connection. I did not realize it until I removed the antenna tuning unit but the twin lead goes to a pin and socket type connector and I think one side was not making up good. I found this out by pushing in real hard and voila my audio came in much clearer. I still have crt disconnected. I resoldered the antenna wires to the pins and squeezed the sockets with some pliers for a tight fit. In response to the reception problem I thought the worse and have been spending last couple weeks learning how to do an alignment or at least how to attempt to do an alignment. I think I the sound IF aligned nicely since I had the equipment to do it with -got a pretty nice S curve. My HP8643a signal generator which was a impulse ebay purchase is a great piece of equip but is limited in its sweep capabilities. It will only do a 600kHz sweep width in its "phase continuous" mode. I got a tip off one off bandersons vids which suggested you could plot curve out on piece of graph paper and that is what I did for the video IF alignment. I will try to post a pic of that maybe tomorrow.

pdr-fml
04-11-2018, 08:37 PM
Here is the result on graph paper after my IF alignment. I know it has some issues but going on some info I've read from different sources it isn't too bad. I think I will purchase a sweeper sometime in the near future so I can more easily touch it up. I plotted every 100kHz.

Kevin Kuehn
04-13-2018, 12:06 PM
Here is the result on graph paper after my IF alignment. I know it has some issues but going on some info I've read from different sources it isn't too bad. I think I will purchase a sweeper sometime in the near future so I can more easily touch it up. I plotted every 100kHz.

It does look pretty good. If you could just slide the lower side to the left a little, so that 22.4mc is about half way down the slope, you will have it very close. As-is your limiting your video bandwidth a little. Also you want your 21.7mc audio carrier to be right in the crutch at the bottom of the slope. Make sure you're using the correct set of frequencies from the Sams chart per your specific chassis number.

pdr-fml
04-15-2018, 10:55 AM
It does look pretty good. If you could just slide the lower side to the left a little, so that 22.4mc is about half way down the slope, you will have it very close. As-is your limiting your video bandwidth a little. Also you want your 21.7mc audio carrier to be right in the crutch at the bottom of the slope. Make sure you're using the correct set of frequencies from the Sams chart per your specific chassis number.

Thanks for the info. I am going to try touching up on it some more. Actually my audio carrier is 21.9 for this set I don't know why they didn't just make them all the same. The good news is that I think I am in the homestretch now. I reinstalled my CRT and after some fiddling around I am finally getting a stable picture. I think my original problem (after I had recapped and replaced tubes and the other standard stuff) was the loose antenna connection. That led me to monkeying with nearly every adjustment so I am still going to spend some more time with trying to get the alignment right. There are some other little problems but I at least I know everything is for the most part functioning as it should. It was pretty cool watching Johnny Carson last night on this 70 year old set!

Kevin Kuehn
04-15-2018, 02:16 PM
Sounds good. So long as you're getting a respectable picture and sound at the same location on the dial, that's really all that matters. :thmbsp: