TV IF alignment

[DaveWM]

I have a B&k 415 and doing a google search I found a thead "B&W alignment almost too easy" but it was back when we had video in the audiokarma forums, nothing comes up when I try that link.

Needless to say it caugh my attention. Looking for some pointers on how to use my new toy, esp after I goofed up an IF alignment on an old B&W tv.

I Have the 415 and a HP 10mhz scope, just dont know how to use it. I am chasing down a manual, trying to get one from a guy that posted in ARF, just sent him a PM, waiting to hear back.

If anybody has heard of a video link that goes thru the process of an IF alignment on a TV I sure would like to see it.

[Phil Nelson]

If you lay your hands on a 1950s TV servicing book, it will usually have a chapter on alignment. Those books are cheap on the used market.

The first sentence is invariably a warning. "Do not attempt alignment unless you are absolutely sure there is no other cause for the symptoms."

I have read the procedures a few times and never been tempted to try it myself, although I have aligned many AM radios and a few FM sets.

Phil

[DaveWM]

well I popped for an eico sweep gen so that will be coming in a couple weeks.

[DaveWM]

If i understand this right, you pic a med point like 44mhz, then sweep that with a 10mhz sweep (34-54) and watch the detected signal on the scope.

Looking for the correct IF shape, using markers to see where the curve is.

At least that is the way I understand it. I have attempted alignments on FM receivers using sweep gens and scope.

I have had a hard time getting results to look right, dont know if its me or my equipment or both.

Anyway I will press on and post my results.

[Adam]

You can see my attempt at alignment, and the RCA alignment equipment in my thread in the b/w forum. For the older sets, you'll need a unit that'll sweep down around 25Mhz. It is interesting to see the different equipment they made. There's that thread about the Sencore units now in the rectangular set forum too. And I remember a post a while ago about an older all-in-one unit that even had the scope built in. I think it was a Philco? I'd like to see a discussion comparing the different alignment equipment that was made, I came down here to start a thread on that but figured I'd post in this thread already here.

I did a quick search on here for threads discussing IF alignment:

Philco unit with the scope built in: http://www.videokarma.org/showthread...ight=alignment
Sencore speed-aligner: http://www.videokarma.org/showthread.php?t=246891
my RCA KCS47 alignment with RCA equipment: http://www.videokarma.org/showthread.php?t=246398
what sweep generators do the older IF frequencies: http://www.videokarma.org/showthread...ight=alignment
aligning a DuMont RA103: http://www.videokarma.org/showthread...ight=alignment
alignment of 1963 Philco color set: http://www.videokarma.org/showthread...ight=alignment
ctc-16 alignment: http://www.videokarma.org/showthread...ight=alignment
sweep generators: http://www.videokarma.org/showthread...ight=alignment
630ts sound alignment: http://www.videokarma.org/showthread...ight=alignment
630 sound part#2: http://www.videokarma.org/showthread...ight=alignment
ctc-15 IF alignment: http://www.videokarma.org/showthread...ight=alignment

[DaveWM]

Great collection of post.

I had some luck with my B&K 415, but I need to review all those others 1st.

I managed to get a trace that looked like it should (well close anyway) and the markers from the 415 are neat as it allows mutilples.

I did check the marker freq 1st since I had no idea of the calibration of the unit, they all tested right on the nose.

the odd thing is the scope had a mirror image with the lower freq markers on the right side and the higer ones on the left.

I had to play with the amplitude some and the AGC bias a lot to get the shape right. Guess that is where the real experiece comes into play.

[DaveWM]

you can see the markers are a little off from where they should be on the left side (hi side) like the slope is too vertical, and there in no visual hump between the 1st two markers where there should be. This is from a working B&W set that looks fine, so I will not mess with it. I have 3 of these particular chassis, all working fine, so the idea is to compare the setups and see how they look. I need to get some confidence that I am on the right track. Then I will try my hand at an actual alignment of a goofed IF (I was the idiot with the diddle sticks) to see if I can make an IF curve look right.

[Adam]

It's reversed from left to right for me too. Mine was also upside down, but I just flipped the vertical polarity switch on the scope.

I can't produce all those markers at once with the equipment I have. It's either 1 marker at a time, or markers spaced 4.5, or 2.5mhz apart. Actually, it says you can take an additional signal generator, and connect it up to the marker generator, setting it to the difference in frequencies between the 2 markers you want, to get 2 different markers at the same time.

[DaveWM]

well I just realized my 415 has a horz seep norm/reverse for the trigger, so I just need to get a cable to hook it up to the external sweep and I should be able to reverse that image.

[DaveWM]

did the hookup of the to horz on scope, rev and normal did not reverse the image, just moved it over, oh well, not a big deal I just wanted it to look like the display on the the 415.... guess I could look at the scope or the 415 in a mirror...

will be hooking it up to another tomorrow, again same chassis just anohter TV so hopefully I can make a pretty much direct comparison, I will leave all the settings alone (bias,sweep,amplitude) and just compare IF strip to IF strip. I hope the next tv has a slightly better curve/marker profile, that way I will know I am getting the correct results. If they match this one, then I have to wonder if I am setting it up right, since a match to the same wrong profile may mean I am detuning something with the hook ups.

[DaveWM]

another set, this time with the injection point being the Osc tube with a ungrounded shield. I added a 44mhz marker, shown in the center of the two main humps

The second from the right is the picture marker, the far right are the two audio markers, there is supposed to be a small hump there, but you cant see it at the bias setting I am using to keep from flattening out the two main humps.

[DaveWM]

I am learning about this OJT, the TP was right next to a IF coil, actually INSIDE the can (removable shield). the shield alone would drasticly effect the tuned response as would the TP leads etc (this is for the demodulated IF signal). Anyway care must be taken for lead dress when hooking up to these TP's.

[jshorva65]

This thread http://www.videokarma.org/showpost.p...26&postcount=8 has a recent post from me which includes my "Top 3" recommended units for alignment of 24 MHz IF systems.

I recently scored the (presumed absolutely Unobtainium, but just REALLY hard to find) RCA WG-295B Video Multi-Marker unit and its companion WG-304A RF Modulator. I haven't found an RCA WR-70 Marker Adder yet, but I have the WR-69 Sweep and WR-99 Marker Generator units. I'm still evaluating the WG-295 / WG-304 and the "VSM" (Video Sweep Modulation) Alignment technique covered in TAB Books' volumes (and other textbooks of the era) on RCA receivers.

The WG-295 and WG-304 are both passive units, the WG-295 establishing its Marker intervals by use of an array of Series LC Traps to create "suck-out" points at its output when a Sweep of 0-5MHz is applied to its input. The output of the WG-295 then connects to one of the two inputs of the WG-304. The desired Picture Carrier frequency is to be injected to the other input of the WG-304. The result is a sweep signal with marker suck-outs at fixed intervals whose Picture Carrier frequency may then be set to any desired value (25.75 MHz for RCA 630TS and similar, 26.40 MHz for Dumont RA-103 and similar, or the RF value of Picture Carrier frequency required for an individual Channel during Tuner Alignment. This setup is adequate, but is subject to the same limitations as any setup which utilizes pre-injection of Markers as opposed to post-injection. An alternate setup using the WR-70 Marker Adder is shown in the Procedures published by TAB et al. Still, the WG-295 / WG-304 setup has proven, although adequate, a bit on the "Rube Goldberg" side.

Has anyone tried utilizing a B&K 415 coupled to one input of a Mixer circuit having a suitably flat response and a fixed Oscillator (20.000 MHz for old-band RCA, 19.350 MHz for old-band Dumont)? Such a setup should shift the B&K 415's sweep output from its 44 MHz center frequency to a center frequency of 24 MHz. Since the B&K 415 uses post-injection for its Markers, however, it seems that a duplicate Mixer would need to be inserted into the Marker channel of the 415, perhaps utilizing a single Oscillator whose output could be fed to the added Mixer stages in both the Sweep-channel and Marker-channel via a buffer amplifier having two well-isolated outputs.

[jeyurkon]

Originally Posted by jshorva65

This thread http://www.videokarma.org/showpost.p...26&postcount=8 has a recent post from me which includes my "Top 3" recommended units for alignment of 24 MHz IF systems.

I recently scored the (presumed absolutely Unobtainium, but just REALLY hard to find) RCA WG-295B Video Multi-Marker unit and its companion WG-304A RF Modulator. I haven't found an RCA WR-70 Marker Adder yet, but I have the WR-69 Sweep and WR-99 Marker Generator units. I'm still evaluating the WG-295 / WG-304 and the "VSM" (Video Sweep Modulation) Alignment technique covered in TAB Books' volumes (and other textbooks of the era) on RCA receivers.

The WG-295 and WG-304 are both passive units, the WG-295 establishing its Marker intervals by use of an array of Series LC Traps to create "suck-out" points at its output when a Sweep of 0-5MHz is applied to its input. The output of the WG-295 then connects to one of the two inputs of the WG-304. The desired Picture Carrier frequency is to be injected to the other input of the WG-304. The result is a sweep signal with marker suck-outs at fixed intervals whose Picture Carrier frequency may then be set to any desired value (25.75 MHz for RCA 630TS and similar, 26.40 MHz for Dumont RA-103 and similar, or the RF value of Picture Carrier frequency required for an individual Channel during Tuner Alignment. This setup is adequate, but is subject to the same limitations as any setup which utilizes pre-injection of Markers as opposed to post-injection. An alternate setup using the WR-70 Marker Adder is shown in the Procedures published by TAB et al. Still, the WG-295 / WG-304 setup has proven, although adequate, a bit on the "Rube Goldberg" side.

Has anyone tried utilizing a B&K 415 coupled to one input of a Mixer circuit having a suitably flat response and a fixed Oscillator (20.000 MHz for old-band RCA, 19.350 MHz for old-band Dumont)? Such a setup should shift the B&K 415's sweep output from its 44 MHz center frequency to a center frequency of 24 MHz. Since the B&K 415 uses post-injection for its Markers, however, it seems that a duplicate Mixer would need to be inserted into the Marker channel of the 415, perhaps utilizing a single Oscillator whose output could be fed to the added Mixer stages in both the Sweep-channel and Marker-channel via a buffer amplifier having two well-isolated outputs.

I considered something similar. But 20MHZ seemed too close to 24MHZ since you're looking at over a 3MHZ bandwidth for the TV and it seemed like the 20MHZ would be difficult to filter out and still achieve a flat response. So I was thinking about upverting it before down converting it. Adding another step.

If I understand the 415 circuitry correctly, you wouldn't have to do much to the post injection if you do the shift from 44 to 24 accurately.

John

[jshorva65]

Originally Posted by jeyurkon

I considered something similar. But 20MHZ seemed too close to 24MHZ since you're looking at over a 3MHZ bandwidth for the TV and it seemed like the 20MHZ would be difficult to filter out and still achieve a flat response. So I was thinking about upverting it before down converting it. Adding another step.

If I understand the 415 circuitry correctly, you wouldn't have to do much to the post injection if you do the shift from 44 to 24 accurately.

John

Interesting point! I'm pretty "rusty" at circuit design in general, and even more so with Solid State and PC Board design work specifically. My last design project used tubes and a hand-wired chassis and that's been a few years ago. Last time I designed anything with a Transistor or IC was nearly 10 years ago, and just a simple Audio device built on a pre-fabbed prototype PC board. Last time I actually etched a board from a published template was over 10 years ago. It's been even longer than that since I designed anything from scratch all the way to board layout and etching. Back before the Net existed and when CAD software and a suitable PC still cost as much as a new car. Back then, photocopying hand-drawn artwork onto special transparency stock sold under a trade name of "Tech 200" and using that like an "iron-on" transfer to get the mask onto a copper-clad board blank was the only way to economically do any kind of one-shot photo-etching. The "Tech 200" stuff also worked nicely with a printed Template from a magazine article provided any flaws in the Original were touched up before making the transfer on the "Tech 200" stock. Basically, the toner deposited on the "Tech 200" would "transfer" (like an iron-on decal to a t-shirt) to a copper-clad board when heated properly with an ordinary iron (or make a serious mess, ruining the "Tech 200" sheet and virtually wrecking the board blank if not heated evenly).