Technical > Electronics > Tektronix 485 - no power up

reply to Mdoc

Re: Tektronix 485 - no power up

reply to neonhomer
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.

DS1824 does light with the power on.

Keep you posted....

Removed comb "U", bent pin 3 out of the way, and plugged it back in. Same thing.

I can't find TP1951...

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

reply to 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....

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

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.)

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

Yes, try that.

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

all wiring to the CRT (leave the HV in)

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

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

reply to neonhomer

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

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

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.