Topic 'Re: Tektronix 485 - no power up' in forum 'Electronics' - dslreports.com

Re: Tektronix 485 - no power up

Sun, 10 Apr 2011 12:13:15 EDT

Mdoc posted :

If I do isolate that line, what should happen?

Theoretically, that it should stop clicking.
If it does, you've successfully isolated the problem.

Re: Tektronix 485 - no power up

Sat, 09 Apr 2011 14:18:49 EDT

neonhomer posted : IIRC, the only way to break that connection is to remove the xfmr board again, and to unsolder it.

I just haven't had the motivation to tear the thing apart again to do it.

If I do isolate that line, what should happen?
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Sat, 09 Apr 2011 14:02:23 EDT

Mdoc posted :

said by neonhomer:

I am beginning to think the problem is with the transformer board, more to the point, the diode box thingy...

That's why I wanted you to isolate it by removing R1602 to confirm that. If you can find an easier way to break the line through R1602 to the multiplier, do that if you can.

Re: Tektronix 485 - no power up

Sun, 03 Apr 2011 04:25:37 EDT

anon posted :

said by neonhomer:

Similar...... but only has 5 pins in it, and I don't believe they are electrically conductive to each other.

I am beginning to think the problem is with the transformer board, more to the point, the diode box thingy...

Well.... I can't find parts for this thing... so do I part it out, or just hold on to it and see if I can luck across another one for parts or the parts I need...

is it one of these? »www.sphere.bc.ca/test/tek-parts/···ts5.html you don't need the exact one, just a compatible one. (same voltage and multiplication) even one from a T.V. that would have the same specs would work. or one could be made with HV diodes and caps..

Re: Tektronix 485 - no power up

Sat, 02 Apr 2011 22:43:53 EDT

neonhomer posted : Similar...... but only has 5 pins in it, and I don't believe they are electrically conductive to each other.

I am beginning to think the problem is with the transformer board, more to the point, the diode box thingy...

Well.... I can't find parts for this thing... so do I part it out, or just hold on to it and see if I can luck across another one for parts or the parts I need...
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Wed, 16 Mar 2011 09:51:22 EDT

Mdoc posted :

said by drjim:

I've probably seen them, but can't visualize what they look like.

It's not one of these! :D

Re: Tektronix 485 - no power up

Tue, 15 Mar 2011 20:54:59 EDT

neonhomer posted : Yeah. I've only bent it out of the way once. So if I have to do it again, I am going to swap it with a different one So I don't stress the same one.

Re: Tektronix 485 - no power up

Tue, 15 Mar 2011 20:20:10 EDT

drjim posted : I've probably seen them, but can't visualize what they look like.
Don't you have to be pretty careful bending the pins out of the way? I'd think they'd crack after a few bends!
--
One man's Magic is another man's Engineering.

Re: Tektronix 485 - no power up

Tue, 15 Mar 2011 18:58:31 EDT

neonhomer posted : No. The combs almost remind me of a resistor pack. It's basically jumper pins in brick of five that interconnect the boards. When I get a chance to tear this thing apart again, I will take a picture of one of the combs...

Re: Tektronix 485 - no power up

Tue, 15 Mar 2011 15:29:18 EDT

drjim posted : You guys keep mentioning "combs". Is that another term for one of the ribbon-type cables that has large pins crimped on the ends of it?
--
One man's Magic is another man's Engineering.

Re: Tektronix 485 - no power up

Tue, 15 Mar 2011 13:28:31 EDT

Mdoc posted :

said by neonhomer:

Okay.... R1602.... problem is this resistor is on the transformer board. So I have to pull the xfmr board, remove this resistor, and then put the board back and then power up the unit.

Is there a way to do this w/o pulling the xfmr board?

Yes, you can do another way, but this will isolate what I don't want isolated: the circuitry for the CRT. You can just remove pin 3 of U comb and put the comb back in, and then test for no clicks. After this, re-insert pin 3.

Remove P1960 (diagram 15). The result should hopefully be that no clicks are heard. If still clicking, the problem is localized to before the P1960. We'll get to that if we get to this bridge.

Re-insert P1960 and do either one of these 2 approaches:
1) Remove everything in the circle (right side of pic above) from the A13 power board and test for no clicks. If no clicks, then re-attach each power line until you hear clicking. When that happens, you've narrowed down the culprit considerably, and that's where you should look much closely for problems. Or

2) Remove power lines singly and test as you go. The approach is similar to above, but inverted.

What you're looking for is a condition where there are no clicks. That's a condition where that part of the circuitry can be ruled out.

I hope the removal of P1960 demonstrates my thinking: that this stops the clicking. If it does not stop, either I'm barking up the wrong tree or my approach is wrong.

Re: Tektronix 485 - no power up

Sun, 13 Mar 2011 23:23:26 EDT

neonhomer posted : No. The resistor is located on the xfmr board, and it is under a cover. So it looks like pulling the xfmr board is the only way. Ugh...

I kinda wish I could have this thing to someone and have them fix it. Unfortunately, I don't have that kind of money...

Re: Tektronix 485 - no power up

Sun, 13 Mar 2011 23:14:25 EDT

drjim posted : How long are the leads on it? You could always clip one lead, lift it, and then solder back to the stub in the board.
--
One man's Magic is another man's Engineering.

Re: Tektronix 485 - no power up

Sun, 13 Mar 2011 22:15:19 EDT

neonhomer posted : Okay.... R1602.... problem is this resistor is on the transformer board. So I have to pull the xfmr board, remove this resistor, and then put the board back and then power up the unit.

Is there a way to do this w/o pulling the xfmr board?

Re: Tektronix 485 - no power up

Sun, 13 Mar 2011 12:54:56 EDT

neonhomer posted : Just a brief update - Still haven't done anything else with the scope. Just haven't felt like dragging it out.

Re: Tektronix 485 - no power up

Tue, 08 Mar 2011 09:31:15 EDT

neonhomer posted : Okay.. will do and post results later....

Re: Tektronix 485 - no power up

Tue, 08 Mar 2011 08:12:25 EDT

Mdoc posted :

said by neonhomer:

Thing is, it only did that when the U comb was removed.

Ah, so it was because the U comb was removed that you saw the flash. OK.

In the last schematic pic I posted, there's a blue dashed arrow. It's pointing at the resistor that connects to the x6 multiplier. Remove it and test for no clicks. (With the U comb in)

Re: Tektronix 485 - no power up

Tue, 08 Mar 2011 00:26:03 EDT

anon posted :

said by neonhomer:

Thing is, it only did that when the U comb was removed.

I didn't notice any continuity between those two pins.

Regardless, I guess I will pull the xfmr board back out and try to clean that area of the board up. I dunno what I can get in there with, maybe a Dremel and a wire wheel on low speed, or a small screwdriver to scrape away the carbon...

the manual says to pull the u comb, bend pin 3 up, then PUT THE U COMB BACK IN. there's a difference from leaving it OUT!. you ARE getting HV!. but the multiplier may be shorted, disconnect that, and see if the clicking stops.

Re: Tektronix 485 - no power up

Mon, 07 Mar 2011 00:14:14 EDT

SmokChsr posted :

said by neonhomer:

I didn't notice any continuity between those two pins.

Not uncommon, think of it this way, the few hundred or so millivolts that your ohm meter uses, don't always find the same current paths that a 3,000 volt power supply will.

Re: Tektronix 485 - no power up

Sun, 06 Mar 2011 23:58:18 EDT

neonhomer posted : Thing is, it only did that when the U comb was removed.

I didn't notice any continuity between those two pins.

Regardless, I guess I will pull the xfmr board back out and try to clean that area of the board up. I dunno what I can get in there with, maybe a Dremel and a wire wheel on low speed, or a small screwdriver to scrape away the carbon...
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Sun, 06 Mar 2011 23:41:44 EDT

SmokChsr posted : If it's flashing HV to ground, Either were getting too much HV or (more likely) something (like a bug) compromised the resistance in that area and caused some carbon tracks.

That calls for a good cleaning and visual inspection and perhaps some HV putty (anyone remember that stuff) or some Krylon Electronic clear after all the carbon tracks are cleaned up.

Re: Tektronix 485 - no power up

Sun, 06 Mar 2011 02:23:39 EDT

anon posted :

said by neonhomer:

What a royal PITA! I managed to weasel the transformer board out of the unit. First thing I noticed is there is a burn mark between pins U3 & U4. U4 is ground.

It looks like U3 is hooked to one of the windings on T1960. One end goes to the 3kv P-P CRT circuit. This looks like it is connected to the 59.4v line, and then continues through a 39ohm and a 470 ohm resistor, then to a diode. This continues to the Balance Node on U1910. Off of this there is 7 resistors for numerous voltages, and a capacitor to ground.

Well, guess it's time to check out this transformer board, and then either leave it apart or put it back in if i don't find anything.

you need to grind off the burned area until you get to clean pc board, that carbon tracking between u3 and u4 at 3KV is like a dead short to it!!.

Re: Tektronix 485 - no power up

Sat, 05 Mar 2011 12:21:04 EDT

Mdoc posted :

said by neonhomer:

I spent a half hour digging on my "flyback" tool (long narrow flat head screwdriver, with a 12" jumper soldered to it halfway down the shaft) last night to disconnect the HV lead. All for not... there was no charge on it.

Heh. No charge? I would think you should get something even though the protection circuit is not letting the inverter get fully turned on.

You checked the resistors, did you check the diodes, too? Check those (not the multiplier, the discrete ones like CR1601 & CR1603).

If so, then... well, let's back-track a bit. You did remove the U comb and the clicking never stopped, right? Time to move on. Try removing T2,T3,T4 (leave T1 and T5 in), check for clicks, and then re-install them and remove the S comb (including T1 link). Did the clicking stop at any time?

If no go, then isolate A11 board by removing DD1, DD3, DD5, BB2, BB5 links. Any change in the clicking?

If still no change, then we need to go somewhere else.

Re: Tektronix 485 - no power up

Sat, 05 Mar 2011 11:03:51 EDT

neonhomer posted : Yeah, the X6 multiplier is a sealed unit.

I did check all the resistors on the board for shorts or opens. They all seemed fine.

I put it back together last night, and turned it on. Click click click click.... Well, I forgot about the scope being on while I was doing something else on my computer. After a few seconds, I noticed the unit was doing something weird.... "click click click .....click click click click" It would click a few times, pause for like half a click, and then keep doing it more.... every once in a while it would pause for a 1/2 second.

I spent a half hour digging on my "flyback" tool (long narrow flat head screwdriver, with a 12" jumper soldered to it halfway down the shaft) last night to disconnect the HV lead. All for not... there was no charge on it.
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Fri, 04 Mar 2011 23:18:07 EDT

Mdoc posted : Also check out the caps and diodes for shorts at the x6 multiplier (red arrow above). It looks like it's on the transformer board, according to diagram 13.

edit: yes, it's on the transformer board. I just noticed that U1600 is a self-contained unit, there isn't a way to test the diodes/caps individually. I'm not sure how you could test it other than with HV probe during operation. But first 3kv must be present.

Re: Tektronix 485 - no power up

Fri, 04 Mar 2011 23:07:24 EDT

Mdoc posted : Congratulations, you've found at least one short, or a burn mark. Question is why did U3 short to ground (U4)? Examine carefully. If there is no foreign matter there, it may be necessary to take measures to insulate U3 from U4 to prevent arcing. But this may not be all to find.

You're correct in your circuit assessment. 59.4v is what is feeding the coil at T1960 to produce 3k volts from it. The 3kv then goes to the red arrow indicated above (diagram 13), and note that this area is still part of the transformer board. The area next to the CRT is also part of the transformer board.

Re: Tektronix 485 - no power up

Fri, 04 Mar 2011 21:16:06 EDT

neonhomer posted : What a royal PITA! I managed to weasel the transformer board out of the unit. First thing I noticed is there is a burn mark between pins U3 & U4. U4 is ground.

It looks like U3 is hooked to one of the windings on T1960. One end goes to the 3kv P-P CRT circuit. This looks like it is connected to the 59.4v line, and then continues through a 39ohm and a 470 ohm resistor, then to a diode. This continues to the Balance Node on U1910. Off of this there is 7 resistors for numerous voltages, and a capacitor to ground.

Well, guess it's time to check out this transformer board, and then either leave it apart or put it back in if i don't find anything.
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Fri, 04 Mar 2011 10:22:52 EDT

Mdoc posted :

said by SmokChsr:

Darn Neo, I didn't realize you were so close.. If you can wait a couple days you can run it up to the shop and I'll take a look at it with you.

Happy troubleshooting!... my parents live in Wesley Chapel.

Re: Tektronix 485 - no power up

Thu, 03 Mar 2011 23:47:09 EDT

neonhomer posted :

said by SmokChsr:

That is if you feel like driving up to St. Aug one evening.

Yeah. I wouldn't mind. Especially if I can get this thing running.

mdoc - Combs "S, T, U, V, & W" on the Power Supply board all go to the transformer board. On pg 4-7, it says to detect a short in the -2950V supply, to pull the "U" comb, bend out pin 3, and put it back in.

I tried it w/ the entire U comb out, and the "flash" was about the same speed as the "click click click".
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Thu, 03 Mar 2011 22:14:34 EDT

Mdoc posted :

said by neonhomer:

Something else. When you disconnect P1960, the unit doesn't cycle. From what I read, P1960 feeds the transformer board.

I just have a bad feeling the transformer board is toast.

I removed the "U" comb and powered the unit up. A visible flash can be seen under the board. The "U" comb is the feed from the power supply board to the transformer board.

Are you talking about the transformer board? And are you talking about a single flash of light? If so, it's worth taking out the board and examining it.

U3 feeds power to the 3KV circuit. U1 IS for the +59.4 circuit, U2 is for +120V, T4 & T2 are the +15 & -15, respectively.

I need to find someone within driving distance of Daytona Beach that I can take this thing to have it troubleshooted more than I can do.

Even if I buy a working scope, it's still going to bug me until this scope works.

If you can find someone, that would be good for you.

This pic shows what you're talking about. You were following "Troubleshooting the Power Supply" on pg 4-7. You're going in the right direction.
--
Descartes: I think, therefore I am.--Christian: I am, therefore I think.

Re: Tektronix 485 - no power up

Thu, 03 Mar 2011 21:42:28 EDT

SmokChsr posted : Darn Neo, I didn't realize you were so close.. If you can wait a couple days you can run it up to the shop and I'll take a look at it with you. I'm swamped right now, (building 2 radio studios, and just had a surprise translator show up today that I had to get on the air.) but give me a little breathing room then I can help. That is if you feel like driving up to St. Aug one evening.

Re: Tektronix 485 - no power up

Thu, 03 Mar 2011 20:55:39 EDT

neonhomer posted : Something else. When you disconnect P1960, the unit doesn't cycle. From what I read, P1960 feeds the transformer board.

I just have a bad feeling the transformer board is toast.

I removed the "U" comb and powered the unit up. A visible flash can be seen under the board. The "U" comb is the feed from the power supply board to the transformer board.

U3 feeds power to the 3KV circuit. U1 IS for the +59.4 circuit, U2 is for +120V, T4 & T2 are the +15 & -15, respectively.

I need to find someone within driving distance of Daytona Beach that I can take this thing to have it troubleshooted more than I can do.

Even if I buy a working scope, it's still going to bug me until this scope works.
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Thu, 03 Mar 2011 16:57:19 EDT

neonhomer posted : Resistance between -9 and +9 points on the board is about 127ohm.

Voltage reading at +9 is between 0.08 to 1.2v
Voltage reading at -9 is between 0.08 to -1.4v

These and all other readings are between GND points on the board and the individual test points.
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Thu, 03 Mar 2011 15:03:18 EDT

Mdoc posted :

said by neonhomer:

+15 : Maybe 1-2v
+5 : 0.2
-5 : -0.2
-15 : -0.2 to -2.4
+59.4 : 0 to 11
-5.5 : -0.5
+120 : 3 to 35
+9 : 0

Assuming you're going to get a scope, in the meantime you could do further checks, based on your quoted post. If there's a short somewhere preventing the protection circuit to allow inverter operation, where is it most likely to be? I think your post might answer this: something on the 9V rail is shorted.

edit: noticed you haven't checked the -9v line. You might want to check the voltage there, and while you're at it, see how much resistance there is between +9 and -9 lines (with power off).

Re: Tektronix 485 - no power up

Thu, 03 Mar 2011 11:06:49 EDT

neonhomer posted : I found a working Hitachi V1100A on Craigslist for $100.....

drjim - I could always ship this thing to you and let you play with it... LOL....

Re: Tektronix 485 - no power up

Thu, 03 Mar 2011 09:14:20 EDT

cowboyro posted :

said by neonhomer:

I think I have reached the limit of my equipment. I hate to have to send this to a shop, as I know it will be a few hundred $$$ to get it fixed.

Yeah you can hunt a working unit if you are patient. I have a 2232 that I got for $100 *shipped*.

Re: Tektronix 485 - no power up

Thu, 03 Mar 2011 00:23:20 EDT

drjim posted : Try and find a local ham radio club. Most of the old guys there (like me!) probably have an oscilloscope, and might be willing to help you track down the problem.
--
One man's Magic is another man's Engineering.

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 23:55:35 EDT

neonhomer posted : Oooookay... Pulled the three connectors that go from the xfmr board to the crt. Nothing. Same thing.

Walked through some of the tests on 4-7. Nothing to note.

I think I have reached the limit of my equipment. I hate to have to send this to a shop, as I know it will be a few hundred $$$ to get it fixed.
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 19:14:28 EDT

neonhomer posted : Haven't forgotten. Just don't feel like opening this thing back up right now. Will probably open back up after the kids go to bed in about 45 min or so.

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 15:07:34 EDT

Mdoc posted : Pull them all off. The big HV lead goes to the tube anode, you can leave that in.

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 14:55:31 EDT

neonhomer posted : You pull the rear cover, and there are three connectors..... one has 3 wires, and two that have one wire each....

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 14:44:49 EDT

Mdoc posted :

said by neonhomer:

Oi vey.. that's going to be a bitch.......

I had the power inverter board and the sweep board out last night, and it was a bitch to get apart.

It says I can pull certain combs to isolate certain areas. I do know if I pull the "R" comb, the "clicking" goes from slow to fast.

The faster clicking is caused by pulling the "R" comb, Table 4-4, pg 4-8, top entry. Nothing new there.

If I'm not mistaken there should be a plug with wires attached to it on the rear of the CRT; you just pull that off.

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 14:30:40 EDT

Mdoc posted : I'll look it up. How fast is fast?

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 14:13:18 EDT

neonhomer posted : Oi vey.. that's going to be a bitch.......

I had the power inverter board and the sweep board out last night, and it was a bitch to get apart.

It says I can pull certain combs to isolate certain areas. I do know if I pull the "R" comb, the "clicking" goes from slow to fast.
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 13:35:00 EDT

Mdoc posted : all wiring to the CRT (leave the HV in)

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 12:04:56 EDT

neonhomer posted : You mean unplug the high voltage lead, or all the wiring to the CRT?

Re: Tektronix 485 - no power up

Wed, 02 Mar 2011 06:35:28 EDT

Mdoc posted : Yes, try that.

Re: Tektronix 485 - no power up

Tue, 01 Mar 2011 22:24:32 EDT

SmokChsr posted : As a quick test I'd unplug the CRT and see if you see a difference. Unfortunately it's not uncommon for a CRT to short.

Re: Tektronix 485 - no power up

Tue, 01 Mar 2011 22:01:00 EDT

neonhomer posted : All I have is a Fluke 789 Process Calibrator, and a Fluke 11 DMM.

I don't know anyone with a working scope. That was the reason I bought one, so I could have one.

I will hae to fight with it more tomorrow. I wish I knew someone locally (Daytona Beach, FL area) who could assist me in fixing this thing. Its either that or I keep searching for a working scope....
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton

Re: Tektronix 485 - no power up

Tue, 01 Mar 2011 21:39:31 EDT

Mdoc posted : And if you can't get a working scope, the best way then is to look at all the inputs to the balance node indicated in the block diagram on pg 3-11 and look for shorts or opens in circuits leading up to those inputs. Look for scorch marks, too. (Cold solder joints is a possibility, too--push/pull on points on the board with a pencil or plastic probe.)