Tektronix Oscilloscope problem

[WM6]

Yes, vertical position circuit (or Y position circuit) belong to vertical amplifier.

Are you tried to connect scope calibration signal (from scope calibration output) to both of scope channel input? It is a square waveform signal. After connecting try with different setting of Volts/Div knob to se what happen. Read manual first.

You say power supply is ok and that you measure all voltages. Does this mean that you measure all voltages on power supply output according service manual? If not, then do this step.

All parts are there for reason, so you need to replace faulty capacitor with new good one.

Regarding safety switch, we now know that reason to safety switch trip was in filter module.
But, not necessary, that this module is someway faulty. Safety switch is working on difference between in-coming and out-coming current (sense possible leak of current to protective ground). Power filters need some leakage current to work properly and can put mains installations conditions at safety switch current limits (about 30 to 300mA depend on factory switch settings) which can be "deceived" trough filter back EMS on scope switch OFF in connection with filter capacitor discharging (so delay in your safety switch trip).

You can try with disconnecting all other electrical consumers in the house and the test scope on safety switch trip, or try to connect your scope power cable to other mains power point in house and see what happen.

[SVEN1]

Here's the Tektronics user group worth joining, 6200 members and everything you ever needed to know on servicing your Tek, along with parts sources, etc.
http://tech.groups.yahoo.com/group/T...guid=334758051

Very active group average 1400 posts a month.

[sido]

Hi Wm6

Are you tried to connect scope calibration signal (from scope calibration output) to both of scope channel input? It is a square waveform signal. After connecting try with different setting of Volts/Div knob to se what happen. Read manual first.

Yes i connected internal calibrated square wave signal. It is present but very small amplitude and varying the volts/div i cannot expand signal on display.

You say power supply is ok and that you measure all voltages. Does this mean that you measure all voltages on power supply output according service manual? If not, then do this step.

I measured all power voltages in power supply section as per Service manual. all are within Spec.

You can try with disconnecting all other electrical consumers in the house and the test scope on safety switch trip, or try to connect your scope power cable to other mains power point in house and see what happen.

Tested and everything is good.

I have posted the fault on the Tek forum. Waiting for reply's. In the meantime i will check all other low power voltages to each sub-section's as per schematic. The schematic's have other low voltage check points and hopefully i can narrow it down to a particular area in the circuit.

Thanks for your help Wm6.

Cheers sido

[WM6]

I have posted the fault on the Tek forum. Waiting for reply's.

Good choice, sido, they should know better than we here.

But one more suggestion. If all with power supply is ok and you can not get satisfying calibrating signal on screen, then we need to go back to Y-Amplifier stage.

There is a circuit (or IC chip) in vertical amplifier stage that commutate both chanel signal together (something like in past popular DIY circuit called commutator that convert one-channel scope to two or eve multi channel scope - the same functionality). Try to search faults (to measure voltage first) around those commutating circuit (IC).

[sido]

Hi Wm6. a bit of update. I got a response from the Tek forum and i am being pointed to the vertical amplifier section also

Here is a quote from a fellow on the Tek forum.....

"Assuming all the low voltage points are within specification then you next suspects are in the vertical output amp section ...starting with Q254-Q257 and working backward. IF any of the low voltage points are out of spec those must be dealt with first"

So there seams to be a problem there wm6 What i have noticed so far is the measured voltage between r266 and r271 at the 6 x 150 ohm resistor voltage divider network. +30v is present in the input of the divider network, but the upper vertical deflection output voltage is +21.7 volts and the lower is +15.1v with unit turned on...They should be both +8.8v. The supposed +8.8v X 2 measured voltages go to the CRT, but do not look to good so far.

The measured on board resistance between each resistor 150ohm's x 6 are all 141 ohms. I think its within spec because me multimeter might not be that accurate at so low ohms readings.

I have done other tests on the sub boards from the front panel and all are good. so it looks like i am in the right part of the main circuit board.

Hopefully i get it going soon. I intend on refurbishing the power supply section to new updated equivalent parts when all is working ok so i get longer life and hopefully problem free for years to come.

Cheers Sid

[WM6]

Hi Wm6. a bit of update. I got a response from the Tek forum and i am being pointed to the vertical amplifier section also

Here is a quote from a fellow on the Tek forum.....

"Assuming all the low voltage points are within specification then you next suspects are in the vertical output amp section ...starting with Q254-Q257 and working backward. IF any of the low voltage points are out of spec those must be dealt with first"

So there seams to be a problem there wm6

Fine, go along their instructions and please report what you find.

Can you post Y-amplifier part of scope schematic here, in readable resolution, to imagine what we are talking about?

[sido]

I hope this is readable. I have a on-line scanned copy of the schematic and is hardly readable for me too.

Cheers Sid

[WM6]

Yes, it is readable, thanks.

But what you posted is Y deflection amplifier, a part of whole vertical scope circuit (yellow marked on block diagram I posted).

My presumption on faulty working is on red marked part of circuit or something around it:

[WM6]

Additional check:

I downloaded 2215 service manual now and found this part of troubleshooting diagram, that suggest this check too: to short momentary delay line leads for check of trace moving:

[sido]

Hi Wm6, only one response from the Tek forum so far. More useful information here and thanks once again to you.

I noticed it says to short the delay lines to see if the beam centers in the middle of the CRT....Does that mean to physically short the delay cable between R338 and R348 on your schematic.

BTW your schematic is for the 2215 model, same principle, but different component labeling. Not a problem here. Circuit block diagram on your 2215 document is slightly arranged different to my 2215A document. See below. Which circuit block are you referring on my document compared to yours posted below??

Another question....when measuring voltages around this circuit is the deflection output wires supposed to be disconnected from the CRT?? See Pic below.

Note: Very hard to work with this Service Manual unless i print out the necessary pages. A large printer paper format would make my job much easier. Will have to copy documents on to USB stick and take it to a large paper print Company for larger schematics or i might print smaller sections as needed.

Cheers sido

[sido]

Which circuit block are you referring on my document compared to yours posted below??

Cheers Sid

[WM6]

Which circuit block are you referring on my document compared to yours posted below??

Cheers Sid

I think your analogue circuit part is to find here:

[WM6]

Yes, momentarily only, and look between shortage at display what happen, then consult troubleshooting diagram I posted:

[WM6]

I noticed it says to short the delay lines to see if the beam centers in the middle of the CRT....Does that mean to physically short the delay cable between R338 and R348 on your schematic.

Yes, you need to physically short it for a moment. Use two (instrument) binding cable with clamp on one side and connect it to delay line leads. Look at display and short cable end for a moment. Consult troubleshooting diagram on what you see on display.

Another question....when measuring voltages around this circuit is the deflection output wires supposed to be disconnected from the CRT?? See Pic below.

No, you don't need to disconnect leads to CRT deflection plates. Probably your voltage is according your beam trace deflection position and you can take it as OK for now. Check first marked commutating circuit that integrate both channel together (measure all voltages around it and check visual part status, if possible measure some parts value - electrolyte C at least if exist).

[sido]

Hi Wm6, I momentarily applied a short circuit to the delay line and the trace did not go center ... actually moved slightly further up on CRT.... therefore the service manual was referring me to the likely cause of fault in the Vertical amplifier section below.

I therefore tested most components so far on the below circuit and have found the Q256 transistor shorting which is starting to look as the problem i am experiencing. Every other component nearby Q256 tested ok.

The part is a LT4403 manufactured by TRW (No longer in Business) and the part has been discontinued.

The only reference to a suitable replacement is a BFR96 as noted below. I cannot even find the datasheet for LT4403 so i can compare pin layout or spec's to BFR96.

I happen to remember i have a few BFR96's from some old UHF radio gear from me radio days, which i will remove and re-fit. I will further test the rest of the components to be 100% certain that the new/used part does not fail again due to other component failure.

Now i got to find where me old radio boards are.

I hope this is me only problem and nothing more with the scope.

Once again Wm6 thankyou for your help.

Cheers Sido