Before we start doing anything drastic like pulling transistors there might be another way of trouble shooting this.

You have a working scope, right? Channel 2 works.
We may be be able to trouble Channel 1 using Channel 2.

Give me some time to come up with a trouble shooting strategy.

 

Here is a up close pic with voltages labeled.

The collector of Q331 goes from -2.14 to -3.26 when ch1 VERT POS is moved full CCW and CW respectively.

 

I also resoldered all parts in question to include the solder joint between ground plane and the bolt below the Q335 label (it was cracked). No change.

Again, Thanks for your time.

-Dave

 

Excellent posts. You are doing a great job!
Give me some time to analyze your findings.

 

Does this have any bearing or has it been narrowed down past this yet?

If it is a step worth doing, what is it that the book is calling the leads for the delay line? It is DL350 board location: chassis; schematic location: 5I

 

You said that CH2 works fine. Hence the problem is before all of this.

 

Your photos with the voltage readings are very clear and easy to follow.

However the readings at Q341 and Q331 are way out of wack.
According to the schematics, here are the expected readings for Q341 and Q331

C -0.7
B +2.1
E +2.9

Your readings are:

Q341 Q331
C -2.93 +2.10
B +1.94 +1.84
E +2.67 +2.67

Set the channel select switch to CH2, set CH2 VERT POSITION to bring the trace to mid screen and repeat the measurements.

 

Set both CH1 and CH2 VERT POSITION to mid range.
Set channel select to CH1 and measure the voltages at the two points shown in RED.
Set channel select to CH2 and repeat the two measurements.

 

---------Left Arrow--------Right Arrow
Ch1 +.79 +4.37
Ch2 +4.37 +.80
Both
ADD +4.39 +4.39

(Left arrow going to R317, Right arrow going to R318)

Voltage in schematic says +.8 and +5.0 coming from the flip flop.

 

When I short across the delay line lead, a trace on Ch1 appears in the center of the display. It cannot be adjusted while shorted.

I know you already narrowed it down past this, but just FYI.

I am not understanding how these voltages in the attached pic highlighted in red and yellow are coming about.

 

Let's back up a bit and move to an earlier part of CH1 & CH2 VERTICAL PREAMPS (Circuit 2).

Set CH1 input select to GND.

Look at Q157 and Q167

Here is what to expect:

C -3.4
B +4.3
E +5.0

We are looking for balanced voltages between the two transistors.

 

Q157
C -3.01
B +4.25
E +5.0

Q167
C -3.76
B +4.25
E +4.84

Definitely not balanced except for Base, but they are in common base config.

 

Me again,

Using the TEK Concept Training for Service Technicians' Troubleshooting Your Oscilloscope: Getting Down to Basics, I used the test depicted in the attachment (I jumpered the base of Q331 and Q341).

I got a trace displayed for Ch1, and it adjusts vertically. Ch1 nor Ch2 adjust the whole vertical range while those two bases are jumpered. So if I am understanding it properly, the problem lies prior to the Q331/Q341 pair.

It may be worth while, if just for the process of elimination to replace Q177/Q187. It seems those specific transistors went out with the BeeGees, although I can find some online shops selling them for ridiculous prices. I'll pull the datasheets for them and see if I have anything close to the specs or order some.



-Dave

 

Here's what I found.

On the schematic, Q177 and Q187 are clearly PNP transistors. In the service manual, replaceable electronic parts section, it lists both of them as NPN transistors Tek PN: 151-0712-00 and Motorola PN: SPS8223.

Xreferencing them in the Tek Semiconductors Parts Catalog (as PNPs) it lists this part as similar: MPSH81

Here is a link to it on mouser: link

Although these are going EOL also.

 

Sorry, I haven't had much time to look at this.
My suspicion is that the problem is earlier than this, possible at U145 on circuit #1.

I would hold off replacing any component until we can narrow it down.

You can try the same thing with Q177 and Q187, i.e. jumper across the input signals at R177 and R187 and see if the CH1 POSITION is working.

Edit: I noticed you've already checked the voltages at Q157 and Q167. Do the same there. Jumper R151 to R161 and see if CH1 can be positioned.

On figure 9-7, A10 - Main board at location D5, measure the voltages at the four pins at W1011 and four pins at W2011.

 

Any time you give is appreciated. Can't complain about free, or especially learning for free.

I jumped Q177 and Q187 and I get a perfect trace in the center on Ch1. It will only adjust vertically about a half inch. Ch2 will fully adjust while jumped.

If I jump Q157 and Q167, I get a noisy trace on Ch1 that CAN be FULLY adjusted to both vertical extents. It is a noisy trace. Same amount of noise regardless of coupling mode. Changing V/Div has no change of magnitude of waveform. Ch2 trace is smooth and can be adjusted fully.

-Dave

 

On figure 9-8, Solder side of A10 - Main board at location D5, measure the voltages at the four pins at W1011 and four pins at W2011 (while CH1 and CH2 inputs set to GND).

 

Looking at the scope, the vertical preamps look like they are from the future (back in the 2213's day). They appear to be the only SMD components in the scope besides the resistor array for the attenuator.

 

W1011
0, +4.85, +5.00, 0

w2011
0, +4.90, +4.90, 0

 

On W1011, jumper the two inner pins, i.e. pins 2 and 3.

I have a hunch that U145 needs replacing. This is a CA3127 in a 16-pin DIP package.
Newark appears to have them in stock.

The one problem is that this will be a pain to have to replace. It is on a postage stamp sized board on the CH1+CH2 ATTENUATOR board and even that is difficult to reach.

But before we do that, there is one more check. If you can get at pins 1 and 9 on the 10-pin board (see circuit #1 at L3) and jumper between pins 1 and 9 (where they show 0V) this might tell us if U145 is at fault.

(I believe this is not going to be easy to do.)