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Mdoc
Ehh... munch munch... what's up, Doc?
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join:2007-03-27
Sterling, VA
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reply to neonhomer

Re: Tektronix 485 - no power up

If DS1824 is blinking, the 115v power is ok up to this point before the inverter and protection circuit. And this means either the startup circuit (VR1831, C1829) is not kickstarting the inverter (Q1834, Q1844) or the protection circuit is preventing the inverter start up. My guess is the latter, but you can isolate that.

To do that, see the first 4 entries in table 4-4, starting on pg 4-7. Make some of the checks noted.


neonhomer
KK4BFN
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join:2004-01-27
Edgewater, FL
DS1824 does light with the power on.

Keep you posted....


neonhomer
KK4BFN
Premium
join:2004-01-27
Edgewater, FL
Removed comb "U", bent pin 3 out of the way, and plugged it back in. Same thing.

I can't find TP1951...


Mdoc
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diagram 14, U1910 pin 2, that's the balance node input. U1910 is part of the protection circuit on A13 power board.


Mdoc
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reply to neonhomer
Click for full size
said by neonhomer:

I can't find TP1951...

Found it.


neonhomer
KK4BFN
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join:2004-01-27
Edgewater, FL
Reviews:
·Bright House
Once you said U1910, I found it.... must be blind... LOL

From ground to the BAL point, I get 60-350mv, and it bounces around....

I get 160V at the shell of Q1834, and between -70 and -140v at the shell of Q1844

So it sounds like T1960 might be bad.....
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton


Mdoc
Ehh... munch munch... what's up, Doc?
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said by neonhomer:

Once you said U1910, I found it.... must be blind... LOL

From ground to the BAL point, I get 60-350mv, and it bounces around....

It's supposed to "bounce around" if you're using a DMM. The proper way to measure is not with a DMM but with a working scope with external trigger on TP1926. For the first 4 entries in table 4-4, do what you can with a DMM. See what you can do to borrow a working scope.

The voltages at Q1834/Q1844 may be from attempts to start the inverter, so it's meaningless at this point. The voltages are supposed to be double the 115v AC input voltage, or the p-p value of the line voltage. Read "Line Input Circuit" pg 3-6 2nd paragraph.

And I doubt T1960 is bad; we can't say it's bad if the problem points to circuits before T1960. It is working (in a manner of speaking) because the secondary voltages are showing the continuous inverter startup attempts made by the startup circuit. Something is preventing this, and the best method to find this out is by monitoring TP1951 with a working scope.


Mdoc
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1 edit
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.)


neonhomer
KK4BFN
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join:2004-01-27
Edgewater, FL
Reviews:
·Bright House
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


SmokChsr
Who let the magic smoke out?
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join:2006-03-17
Saint Augustine, FL
reply to neonhomer
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.


Mdoc
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reply to neonhomer
Yes, try that.


neonhomer
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Edgewater, FL
You mean unplug the high voltage lead, or all the wiring to the CRT?


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


neonhomer
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Edgewater, FL
Reviews:
·Bright House
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


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


Mdoc
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reply to neonhomer
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.



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


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


neonhomer
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Edgewater, FL
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.


neonhomer
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join:2004-01-27
Edgewater, FL
Reviews:
·Bright House
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


drjim
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join:2000-06-13
Long Beach, CA
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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.


cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to neonhomer
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*.


neonhomer
KK4BFN
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join:2004-01-27
Edgewater, FL
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....


Mdoc
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1 edit
reply to neonhomer
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).


neonhomer
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Reviews:
·Bright House
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


neonhomer
KK4BFN
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join:2004-01-27
Edgewater, FL
Reviews:
·Bright House
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


SmokChsr
Who let the magic smoke out?
Premium
join:2006-03-17
Saint Augustine, FL
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.


Mdoc
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reply to neonhomer
Click for full size
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.


neonhomer
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Edgewater, FL
Reviews:
·Bright House
reply to SmokChsr
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


Mdoc
Ehh... munch munch... what's up, Doc?
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reply to SmokChsr
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.