Help with a B&K 1077PAL
 

Yes, really, they exist, and I have one!

https://i.imgur.com/BofIs3Ml.jpg
https://i.imgur.com/T2eXFW0l.jpg

I bought this online from a--well, basically, a junk dealer. He got it from another junk dealer, and had no idea if it worked or not (spoiler: it does not).

The only reference to this thing I can find online is the ad I bought it from. No schematics, manuals, nothing of the sort.

I was excited to get this, hoping to have a signal source to start work on this growing pile of TVs in my garage. It has a Type B (US-style) grounded plug with the ground pin cut off, and this notice printed on top:

https://i.imgur.com/Pwq0NILl.jpg

There is no means to switch voltages that I can find. And the power supply looks pretty much like the one in the schematic for the 1077B that's out there on the net, so I can't figure out how this thing is supposed to work over such a huge range of voltages. Based on the plug, I'm planning to stick to 120V for the time being.

I tried to bring it up on a variac (following Phil's excellent-as-always article on his 1077) and...dead. I checked the fuse and here is our first sign of trouble:

https://i.imgur.com/QsWfiWcl.jpg

But it has continuity, and in theory ought to power up, so I took off the bottom. Shit.

https://i.imgur.com/3SV8XQgl.jpg


The HV rectifier socket has a big hole burned through it. At first I thought it had arced, but there is no sign of any arcing on the socket itself, so I figure it may be ancillary damage from when that green thing that used to be a resistor burned up.

It also appears to have had a number of the power supply components replaced with contemporary diodes and electrolytics:

https://i.imgur.com/PRcXjxql.jpg

So, I have some questions:

- The line voltage has me really perplexed. I've gone through it again just now, and the power cord pretty much goes right to the primary of the transformer, no 110/220 switch that is typical of European products from this era. Any ideas here?

- I'll start troubleshooting around that burned up resistor and hopefully the schematic will be close enough to follow along, and figure out what caused that to happen, but what about that giant hole in the HV rectifier socket? Scrape out the carbon and goop it with silicone, or do I need to try to replace it? Finding another one will be a challenge.

- Several of the electrolytics have been replaced, but the main filter in the can and the ones on the PCBs are all original - is it safe to assume I need to replace all of those?

- The flyback looks to have been pretty toasty during its life, is this normal for one of these? I don't have a ringer but can ohm it out to get an idea if it's open or not.

https://i.imgur.com/lCBId6jl.jpg

Any suggestions, advice or other comments are most welcome!

On the American units they were 120/240v as well. They typically came wired for 120v. How they did it is to have 2 120v primary windings on the transformer. You would wire the two windings in parallel for 120v and you'd wire them in series for 240v. If there's only one winding on yours and no taps then your stuck with that voltage... you can test for correct input voltage by observing heater or b+ winding voltage.

I'd try to fix the cup like you suggest before replacing it.

Hopefully your power transformer is still good... lot of factors there worry me.

Without a schematic that's going to be a challenge if there is any more wrong besides the power supply.
Yes, I would replace all the power supply caps. For all you know one of those replacement caps was installed wrong and caused the resistor to overheat.
You may have to trace out and make your own schematic for the power supply. Can you even figure out the value of the burnt resistor? You may have to assume that it is the same as the PS in a NTSC unit.
I think you can clean and patch the HV socket.

Well I dug in a little more and scraped the carbon off the socket. It turns out it was arcing, from where the HV anode lead is soldered to one of the pins in the socket. Somehow that melted resistor, which I have determined to be R-106, 220Ω 7W, measures 219Ω. The various sections of C8 (the main filter) also seem to be OK.

Tracing the power cord to the power transformer, one of the terminals on the transformer has a jumper soldered across to the other side of the transformer, and there is about half an inch of light-green wire soldered to this same terminal that has been cut. My best guess there is that this is the series connection for the two primaries that Tom C is talking about.

I've scraped out all the carbon I can from that socket and dressed the wires away from it. Tonight I will bring it up on the variac again, this time to 240V, and see if I get any fireworks while I wait for some silicone to be delivered.

Thanks everyone for the input. If anyone has one of these and feels like taking a few photos of the way that power transformer is wired it would be really helpful.

Put a meter on the heater voltage when you try for 240 if 6volt tubes are getting 6 at 120 input then your unit is wired for 120 and feeding it 240 will damage the power transformer.

So far, so good! Running it a 240V I have correct filament voltages, and the pilot is lit in standby mode. I also have ~300V at the output of the secondary, before the standby switch, across the first filter. I didn't turn it on due to that gaping hole up there, and the insulation burned off of the B+ wires. Tomorrow I'll try to get my hands on some silicone and patch it up, replace the burned wires, and bring it up slowly to see if it will work.

Thanks again for all the advice everyone.

There is no way all that damage came from arcing alone. For one thing the HV rectifier couldn't conduct enough current to do that. The white cup probably charred from the heat of the resistor and it arced as a result. The wire in that resistor probably was at least red hot to soften the green coating.
The heat also charred the wires. Something caused the excessive current through that resistor.

Yeah, that is my thought too. Here's where I am: I cleaned up the burned wiring, checked resistance on all of the B+ lines and found it fairly high, and brought the device up slowly on a variac. At 235VAC, I have all three B+ sources putting out the exact 225, 150, and 75V that they should; powering on and off I can see the filters charge up and back down as expected. That melted 7W 220Ω resistor gets pretty hot, but I think that's to be expected under normal operation.

The bias supply works as expected.

The screen on the CRT doesn't light, and I'm not getting much of any useful signals from the various jacks around the front panel:

I do have 1kHz audio, though the waveform isn't exactly a sinewave - it looks more like, I dunno, nipples from an old-school baby bottle, I guess?

The vertical sweep drive has a very messy sawtooth waveform. Horizontal has nothing. Nothing on Sync, nothing on Color. I haven't tried the others yet.

So I don't know what caused that meltdown, but it seems it's not there now - a screw fell out when I took the bottom off, I wonder if it had maybe shorted that B+ line to ground? Tomorrow I'll start trying to track down what's not working right, I'll check for boost, and see if there's any other test signals available. Since I really don't understand how this whole circuit works I'm kind of feeling my way in the dark.

If you don't have a horizontal waveform or a light screen then the H osc is not running...It is the same basic circuit concept as a TV H system except for a second H output tube to safely drive an external flyback.

Is the CRT filament lit? And is the ion trap in approximate position? I think they're pretty easy to fix. I found one behind an abandoned TV shop in a shopping center that looked like it had sat out in the rain for 6 months. After drying it out in my furnace room, I only had to change some hi value resistors and capacitors.
It should work on NTSC with no problem. The vertical gets its reference from the power line and you should be able to crank on the HORIZ control on the front panel to slow it down to the NTSC rate. To get the color to work, you'll have to change the 4.43 crystal to 3.58.

:saywhat: Why would he want it to work on NTSC ? I thought the whole reason he was so happy about getting it is specifically because it does PAL , if he needs NTSC there are lots of those units available VS this being the first PAL unit I've ever seen .

Given he lives abroad in a PAL country I'd imagine the PAL version is better for him.

Yeah, I am (or was, I guess) in a PAL country. Most of the sets in my growing pile are CCIR pre-PAL, though I do have a pre-NTSC Predicta, and a goofy-looking bright orange space-age Telefunken PALColor 616. I mailed B&K about this thing asking if they had any documentation, and they told me they never made a PAL version. :)

To answer kf4rca's questions, yes the filament is lit, and the ion trap is in place and hasn't been moved from its original position as indicated by the red mark and copious adhesive. There is no high voltage. I found the original manual and it actually has a brief description of each of the circuits so I'm going to start troubleshooting like it was a regular TV with no HV and see where that gets me. I'll cross the why-are-there-two-horizontal-output-tubes bridge when I get that far.

:) Hi Alan , Tom has already disclosed why there is a second horizontal output tube , one of them is to drive the B&K unit's own (internal) flyback , and the second is for driving an external flyback , presumably in the TV set being repaired by the user of the B&K .

Yup!

That's funny. I hope you emailed them a picture of the impostor piece of equipment. Possibly there was another B&K division over near your country that made them.

Nah, I didn't bother, the lady mailed me the same schematic for the 1077 that is floating around the web.

OK, another day, more head-scratching. I probably picked a tough place to start this hobby, but I'm in it now and hopefully I'll see it through to the end. I really don't understand the architecture of this thing. On a high level yes, but getting down into detail I'm confused. This goes to more general TV circuits and not just the 1077. Here's my understanding, which is clearly wrong, no need to be gentle:

https://i.imgur.com/TK8jyxFl.png

The horizontal and vertical oscillators depend on boost voltage (vs B+) for their plates. The boost generally comes from discharging a capacitor (which I don't see in the 1077) off the damper tube, which conducts as the magnetic field in the flyback collapses after the horizontal output tube stops conducting at the end of each scan line. So...if the horizontal oscillator is not running, there is no pulse on the grid of the horizontal output tube, which does not conduct, which does not cause the magnetic field in the flyback to collapse, which does not cause the damper to charge the capacitor, which means there is no boost so how does the horizontal oscillator start with nothing on its plate? I can see the chicken but there seems to be no egg.

Someone please straighten me out!

The set starts on the 225v B+ supply which has a DC path from the boost supply back through the flyback then through the damper to the 225 rail.... the 225 starts it then once the osc starts switching the output generating boost the boost adds to the 225 it started on.

Voltage checks against the schematic are a good starting point in major failures like this.

Thank you for that. Now I get it.

I was able to track the problem to a shorted filter capacitor (10uf/450V) in the decoupled boost supply that took out a 4.7k resistor. I replaced those pieces and now could hear the horizontal oscillator running (the frequency sounds low to me, especially for PAL).

But I still had no high voltage, and no screen illumination, so I started poking around. I didn't measure the plate of the horizontal output tube since Sams always says DNM on those, but checked the cathode and had about 10V, so presumably there was current flowing through the tube.

I decided to look at the grid with a scope to see if I have any drive, and got a waveform that resembles those I see in tube TV schematics, sort of a cross between a sinewave and a sawtooth. I saw pretty much the same thing on the HORIZ GRID DRIVE jack, and the grid of the top half of the 6FQ7 horiz osc; the moment I touched the probe to the grid of the bottom half of this tube, the horizontal oscillator got much, much louder (still at a frequency that I don't think seems high enough but not really sure), and checking again I have about 4KV of high voltage - no idea what the number should be, there are no voltages on the schematic. And still no raster.

https://i.imgur.com/ZA8HArtl.png

I have double-checked the PCB and don't think it was a mechanical change I made to the circuit when I touched that grid, and poking around further didn't cause any other change. It would really be helpful to have some voltage measurements. Tomorrow I'll get back to it, but for today I'm pretty excited about the progress. Thanks everyone for the help and suggestions.

The schematic shows that C30 is 470 pf. It is part of the frequency determining components. It may be a different value for PAL. The stray capacitance of the probe changed the total on the grid and so probably changed the frequency.

I should have been more clear. The oscillator changed when I touched the probe to the grid, but stayed that way once I removed the probe. It's like I started it, or something.

My manual says approximately 12.5kv for the CRT. Theory of operation starts on page 104 of the manual.

That's interesting. It could be that touching it brought the frequency more in line with what it should be. The flyback circuit performance is frequency dependent so if it is far enough off the generated voltages will be low. This includes the boost which is used to power up the horizontal oscillator. So maybe touching the grid caused the frequency change that increased the boost that got the oscillator running better. This may indicate the oscillator tube or other part that changes with voltage.
BTW, I've got a schematic for the 1076 and a voltage chart for the 1077B that both show the CRT anode voltage to be 11.5 KV.

We. Have. High voltage! There were a few dodgy-looking solder joints around the horizontal oscillator tube socket; I repaired all of them, powered back on, and:

https://i.imgur.com/ekpq5Dvl.jpg

So, it's a looong way from working, but every bit of progress is encouraging.

• There's about 300V of boost, and HV of about 9.5kV.
• The H frequency is way off (way too low), and you can't see very clearly in the photo but the horizontal has a big bright line down the middle. The raster is only about 1cm high, and awfully jiggly.
• Cranking on the CALIBRATE control varies the pitch and intensity of the horiz oscillator, with a tiny bit of change on screen but not much.

At this point it all seems solvable, and it's probably time to start replacing those capacitors and checking resistors. On a whim I checked C30 (it's 390pf in my model) and it's right on the money. I connected a frequency counter to the horiz drive socket and it says 12.925khz. If that is correct, it's not a small amount.

That's great. I don't know what the PAL frequencies are, but you shouldn't have too much trouble finding out.
I suppose you know you should turn the intensity down so you don't damage the CRT phosphor down the middle of the screen.

Yes, I'm pretty stoked! PAL horiz frequency is pretty close to NTSC 15,625Hz, and just found what I guess is the intensity control on the cathode of the CRT - I'll lower it, good suggestion.

According to the service manual:

I can't find anything resembling a frequency adjustment in the horizontal oscillator circuit - could it be something besides a potentiometer?

It seems to me that R52 and R53 are the most likely causes of the off frequency, along with C101. That's what I'll check next.

The horizontal freq is derived by a divide by counter(CD4013) driven by the color burst oscillator. There's a trimmer cap(C100) in series with the color crystal in the grid circuit of V6A that should allow some adjustment.

Before I'd worry much about the horz frequency I'd be looking for the cause of your vertical deflection collapse. Possibly a bad cap, connection, or tube in the vertical section. Possibly even the vertical height or linearity controls.

You'll probably have more correct boost and HV when you get the horizontal frequency on spec. I haven't seen the h osc circuit schematic of one of those in years, but the osc is probably adjusted with a slug tuned coil or possibly a trimmer cap...Dirty secret of most TVs with a hold pot: the pot is the fine frequency and often varies the effect of the AFC tube that pulls the frequency of the oscillator...The course hold is usually slug(s) in the H osc transformer (some sets especially Zenith and portables did away with the pot and made the transformer slug the user control).

On some sets, the boost also feeds the vertical osc/output, and powers other stages...If the vert stage is defective in such a way that it is loading down the boost rail it could be causing the H osc to not get enough boost to run on frequency...May want to prioritize vertical and troubleshooting of boost powered stages first.

BTW may want to pull the photomultiplier tube if you are operating with the lid removed and fluorescent shop lighting. The flying spot CRT produces ultraviolet light as does some non-incandescent lighting (especially fluorescent) and if you overload the photomultiplier with more ultraviolet light than the CRT makes you could damage it.

One thing to keep in mind with this series of instruments is that unlike a TV set where the deflection circuits are intended to sync to an external signal, these instruments originate the sync. Of course the intent is to generate these signals to the relevant standard.

So. Bump I guess. I have the exact same symptom as that photograph. I.e. virtually no vertical deflection. Mine is a 1077B and the horizontal oscillator is fed by a couple of J/K flip flop ICs. I have found one circuit diagram with that arrangement, but my circuit is different in that it has a 8FQ7 rather than a 6FQ7. I can’t find a voltage chart that I can be sure matches my circuit so testing the voltages of that tube seems a little pointless.

I have a CD coming that supposedly has the 1077B manuals on it - we’ll see. In the meantime I wonder if you got to the root of this problem (lack of vertical deflection).

Is your circuit board designation marked as 8GC7? If not it's possible the previous owner was following the wrong schematic. I have two 1077 schematics here and on the 8GC7 version it does not use the JK flip flop. There's a possibility that there are revisions of this devise we're not aware of. Otherwise for loss of vertical check the 50uf cap on the cathode of V1B vertical output. Other than that you pretty much have to get in there with a scope and see where you're loosing your vertical waveform amplitude.

The label that shows the tube placements has it as a 8FQ7/8GC7. The voltage on the cathode of V1B is correct and flat on an oscilloscope, though the vertical disappeared after I replaced the the electrolytic can with new electrolytics. Basically I’ve checked a bunch of voltages and resistor values. I’m trying to get my hands on the voltage specs for a 1077B. They are different than the 1077, so until I get the right ones I’m not going to spend any more time on it, unless the OP chimes in with what happened with their unit.

The 8FQ7 and 6FQ7 are the same exact tube with the exception of heater voltage. The 6FQ version probably has a 6V heater transformer with parallel wired heaters and the 8FQ is probably a series wired heater unit. If the heaters are the only circuit difference and they are lighting properly then you can use the voltage chart and just ignore the heater pins...

Hi Tom,

The schematics with the 8FQ7 and the 6FQ7 both have them series wired. Makes me wonder if the designation is an error in the schematic. It would be interesting to hear from someone else with a 1077B what tube is actually installed.

Not getting anywhere with this. I’ve replaced the 8FQ7, which has no effect. Test point 17 shows a good waveform. At test point 3, it also looks good until I move the switch from stby to on, then the peak to peak voltage drops from 12 to 7.6. At test point 5 the peak to peak voltage is around 90, it should be 120. I’ve tested all the resistors around Q1 and Q2 and they appear fine. In my version the B-13 rail also powers Q4 and the J/K flipflops. Other than that I can’t find anywhere else it is used. I also checked the resistors that are used to form the negative rails, they are all fine too and I replaced those capacitors.

Just in case I tried a different cap to pin 3 of the 13GF7A, it made no difference, and anyway voltage on that pin is fine.

I wound up finding a modern Philips device with similar functions so I put the 1077 to the side while I work on the pile of TVs I have.

If anyone has a working 1077B with the J/K flipflops, could you test the B-13 rail when the unit switch is 'on' (not 'stand by')? It would help me rule out a whole section of the circuit, or narrow the problem down to precisely that part of the circuit.

Hey everyone, remember this? I pulled it back out to continue working on it and have replaced a couple more electrolytics that were shorted and had related open resistors.

Only one problem now...when I put it in storage it had a raster, more or less, but only have about 1cm of vertical sweep. The entire vertical circuit is working OK but no sweep. One of the vertical deflection coils measures 34Ω, the other measures 156K. So, it's not exactly open, and I have never had occasion to measure the dc resistance of a yoke before so I'm not sure, but it seems to me that this is likely my problem.

Any opinions on why it failed and if it might be fixable? I'm pretty sure I'll never find a replacement. An additional challenge is that I'll probably also never get it off the crt; the base is already slightly bigger around than the neck of the tube, and the plastic of the yoke has shrunk so that it is very tight on there.

ETA: came across an old Shango video where he repairs a yoke with the same problem and says it's common on the 1077s. It looks like quite a job.

OK, I got the yoke off and managed to get it apart following the old Shango video. He says that he's repaired 3 1077s with bad vertical windings, and says you have to look for the "green", where there is a little spot of corrosion. The one he repairs in the video has a clearly broken wire right under the spot. Wire reattached, and the device works again.

My yoke had an identical green corrosion spot in exactly the same place as the Shango video, but the wire is intact. In fact I've spent the last hour with my 3.5x goggles going over every part of this yoke and can't find any broken/corroded wire. Verified that the winding measures 1.2M.

A couple of questions: first, shouldn't it measure open? What's going on there?

And second, how does one go about finding the point of failure? I'm pretty sure it's not on the surface. Are yoke windings interchangeable to the point that I might be able to pull one (either a yoke or another winding) off of another set? I guess it would have to be one with a really narrow deflection angle...

Thanks everyone.

Maybe it will be worthwhile to get a yoke from a USA 1077, but I do not know if it will be different due to the line and frame rate differences.