Tek 2215. Vertical Amplifier Issues.

[M3VUV51]

Hi all,ive just brought a tek 2215 60mhz scope for spares or repair for £15,it has an issue with the trace being positioned way low on the screen,if i inject a sine wave into it ,half of the trace is bellow the bottom of the screen,the position knob only moves the trace to the midpoint on the screen,it does it on either channel,i have checked the resistors around the deflection plates and they measure fine,my guess is transistors q386 and q 387,apparently these are q386 is = to a brf96s and q387 is = to a 2n2369a,they are both npn,could i use a bc 108 or a bfy 50 as subs for these anyone?

[frsimen]

The BFY50 with its FT of 50MHz isn't a good substitute for a 3.5GHz BFR96S. The BC108 isn't quite as far off the mark but is still not ideal.

If all you want to do is prove a point, they may do for a quick test, but the 'scope is unlikely to meet its specified performance with the substitutes you are proposing.

I think I would prefer to do some simple meter tests on the transistors that are fitted to confirm whether or not they are actually faulty.

Paula

[Diabolical Artificer]

It sounds more like a DC or trace offset issue. I'd look at the manual first and see if there is a preset to adjust the vertical.

Andy.

[M3VUV51]

the transistors test ok with betas of around 80,the two resistors that feed the deflection plates measure 57 ohms,they should be 51,could that cause it?,im running out of ideas now.

[dave cox]

Do you have a 2nd working scope to diagnose this ?
( some say this is essential with an old Tek scope )

It is usually possible to diagnose with a meter only, as this amp will work down to dc.
This output amplifier drives the plates in anti-phase from 2 identical single ended amplifiers.
1st check that the dc voltage on the output plates while adjusting the position.
Do they both change ?

dc

[loulou31]

Hi
the transistors test ok with betas of around 80,the two resistors that feed the deflection plates measure 57 ohms,they should be 51,could that cause it?,im running out of ideas now.
No the problem is ouside of these components.
Did you check positive and negative power supplies mainly high voltage power supply ( about 100 to 150V) used to the last stage of deviation amplifier?

Jean-Louis

P.S : there is a Tektronix very good publication that explains how to repair Tek oscilloscopes https://www.sphere.bc.ca/test/tek-pa...ing-scopes.pdf

[loulou31]

Hi

I have checked the output stage of the tube and there only one 30DV power supply.
Could you check voltage on base of Q350 and Q360? The differential voltage can be positive or negative following trace position.

Jean-Louis

[Diabolical Artificer]

1st check that the dc voltage on the output plates while adjusting the position.

Meter set to DC volts, black probe to ground, red probe to vert plate, even better two meters each on one vert grid/plate. When V position adjusted, one should go up in value, whilst the other goes down,they should seesaw. As your trace is stuck at the bottom, it follows that that one vert driver is stuck. The vert position is adjusted by a pot, have you checked it? Check any caps around the driver circuit too, a shorted or leaky cap will screw with DC conditions.

It's good to include a schematic and pics of the circuit in question in your threads/posts, you may more answers that way. We may see something you've missed.

Andy.

[tony brady]

it's also worth checking if one of the Y deflection wires going to the side of the tube has come off

[PJL]

The service manual is readily available.
First check the power supply rails (5.3 page 74).
The vertical amplifier is covered on page 159. The differential amplifier starts at Q331/Q341 and runs through to Q377/Q387. There are various voltages marked up and I would start by setting the scope on channel 1 only and adjusting the vertical position so it is as near to the centre as possible then check the base voltages against those in the manual.

[M3VUV51]

well ive measured the deflection plates,the top one when viewed from the sidemeasures from -3v pos control fully ccw to 16v fully cw,the lower plate sits at 20v with no change when the pos pot is moved,thesr measurments are relative to chassis ground

[M3VUV51]

i would if i could find the test points on the pcb,all i can see is ground.

[M3VUV51]

Well,i located the test points,all the voltages are within about 100mv of what the manual states.

[Diabolical Artificer]

the lower plate sits at 20v

Right, there's your problem, or one of em. Can't read the schematic you posted, hold on, I'll download the manual.

Right, if in doubt follow the first rule of electronic diagnosis "Thoult shalt check voltages" If by lower plate you mean that connected to Q386/387 then take voltage readings and compare to the schematic. The scan I have isn't very good and I haven't read the manual but it looks like you should have -14v on the plate and emitter of Q387 (when vert position set to midway?), then work your way back, check Q386's base V, working your way back to Q360.

If you look, at R361, it says 8V6 (2?), that looks like a zener voltage, a V reference, I'd check that.

If you get lost, follow the second rule of electronic diagnosis "Read the manual" Tektronix made very good service manuals, in yours it will have a vertical amp circuit description. You have to have at least a rough idea of how things work, blindly checking components only gets you so far. Inna nutshell the vert amp is just an amplifier, albeit one with a wide frequency range. It will have an input, preamp, driver and output stage.

Therefore it follows if the OP stage is playing up, first check it, then the driver, then the preamp.

Hope that helps, Andy.

[DMcMahon]

[QUOTE=Diabolical Artificer;1416987]

If you look, at R361, it says 8V6 (2?), that looks like a zener voltage, a V reference, I'd check that
Hope that helps, Andy.

I see that the +8V6 (2) is one of many numbered separate +8.6V rails that are derived back through the power supply distribution wiring connections back to main +8.6V supply that is derived from bridge rectifier (diodes CR971 - CR 974) followed by filtering components.

Some of the separate numbered +8.6V rails have in line resistor plus capacitor decoupling.

David

[Diabolical Artificer]

I see that the +8V6 (2) is one of many numbered separate +8.6V rails that are derived back through the power supply distribution wiring connections back to main +8.6V supply

Ah, so no zener. I didn't look at the PSU. For the bottom end it's MINUS 8.6v.

Some of the separate numbered +8.6V rails have in line resistor plus capacitor decoupling.

Those R's & C's will need checking if you haven't got -4.3v on Q386's base.

On looking closer at the V OP stage I see it's AC referenced to ground by C399, worth a look at. The vert plates are tied to a +30v source, through a potential divider consisting of R368/9 & R 378/9 four 340r resistors, check em. This means that the plates are not DC referenced to 0v, but offfset. Hard to read the voltages but it looks like you should have +4v on one plate and - 49v on the other.

I also see the V driver stage is connected to the beam finder button, so what happens if the beam finder button is pressed? It should center your trace in the center of the CRT. If it doesn't something else to investigate.

As a meddler and fixer of old Tek scopes I've found you have to be systematic as mentioned in post #14. Print off the vert OP schematic, check your voltages and write in blue all voltage reading you find in blue say, the wrong readings in red. Another thing I try and do is keep a record of what I've done in a notebook, it's easy to get lost, go round in circles and get nowhere with complex gear like this.

Good luck, Andy.

[M3VUV51]

Is it OK to power it up with the CRT out of the unit, or will it cause issues with the anode disconnected?

[DMcMahon]

Originally Posted by Diabolical Artificer

Ah, so no zener. I didn't look at the PSU. For the bottom end it's MINUS 8.6v.

Yes I incorrectly read the post as +8V6 so followed that, as you say the -8V6 comes off the bottom end of the same bridge rectifier and my comments about the separate numbered rails equally applies.

David

[M3VUV51]

trouble is i cant do anything realy without powering up the scope,as it has the crt removed,finding out if its ok to power on with the crt removed is the most important thing,i am suprised no one seems to be able to answer this !!

[M3VUV51]

look at post 17 folks.