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  #1  
Old 12-06-2018, 06:41 AM
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AlanInSitges AlanInSitges is offline
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Help with a B&K 1077PAL

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




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:



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:



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




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:



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.



Any suggestions, advice or other comments are most welcome!

Last edited by AlanInSitges; 12-06-2018 at 06:53 AM.
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Old 12-06-2018, 10:36 AM
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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.
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Old 12-06-2018, 10:46 AM
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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.
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Old 12-06-2018, 11:36 AM
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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.
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Old 12-06-2018, 12:05 PM
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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.
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Old 12-06-2018, 07:19 PM
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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.
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Old 12-07-2018, 12:21 AM
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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.
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Old 12-07-2018, 06:05 PM
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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.
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Old 12-07-2018, 07:35 PM
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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.
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Old 12-08-2018, 03:14 PM
kf4rca kf4rca is offline
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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.
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Old 12-08-2018, 07:29 PM
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Quote:
Originally Posted by kf4rca View Post
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.

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 .
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Old 12-08-2018, 11:50 PM
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Given he lives abroad in a PAL country I'd imagine the PAL version is better for him.
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Old 12-09-2018, 06:08 AM
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AlanInSitges AlanInSitges is offline
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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.
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Old 12-09-2018, 09:18 AM
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Quote:
Originally Posted by AlanInSitges View Post
I'll cross the why-are-there-two-horizontal-output-tubes bridge when I get that far.
Quote:
Originally Posted by Electronic M View Post
...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.
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 .
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Old 12-09-2018, 11:09 AM
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Quote:
Originally Posted by init4fun View Post
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!
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