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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 6:25 am 
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tbone8 wrote:
It was set on 50μs.

I mean the horizontal display mode: A, A Intens, Alt, B Delayed.

I suspect Q2105 is the culprit, unless you had the horizontal display set to ALT. (Kind of like a game of Clue:" I suspect Col. Mustard in the Green room with the lead pipe." :-) )

Would you please measure the voltages on the emitter, base, and collector of Q2105? And check the base-emitter and base-collector junctions with the diode check function on your DMM?

On the other hand, your resistance measurement between pins 2 and 3 of U2225 is suspiciously low. I don't know the value of the internal resistor in U2225, but judging by the other resistances in the bias network, I suspect it should be much larger than roughly 30 ohms. But let's check Q2105 first.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 6:48 am 
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stevebyan wrote:
tbone8 wrote:
It was set on 50μs.

I mean the horizontal display mode: A, A Intens, Alt, B Delayed.

I suspect Q2105 is the culprit, unless you had the horizontal display set to ALT. (Kind of like a game of Clue:" I suspect Col. Mustard in the Green room with the lead pipe." :-) )

Would you please measure the voltages on the emitter, base, and collector of Q2105? And check the base-emitter and base-collector junctions with the diode check function on your DMM?

On the other hand, your resistance measurement between pins 2 and 3 of U2225 is suspiciously low. I don't know the value of the internal resistor in U2225, but judging by the other resistances in the bias network, I suspect it should be much larger than roughly 30 ohms. But let's check Q2105 first.


Sorry, its in A mode. Q2105 is soldered to the darn board I will try to get readings on it but will they work being attached? Good grief... :(


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 6:52 am 
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tbone8 wrote:
Sorry, its in A mode. Q2105 is soldered to the darn board I will try to get readings on it but will they work being attached?

Yes, you can check the transistor junctions in-circuit using your DMM's diode check function.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 7:05 am 
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stevebyan wrote:
tbone8 wrote:
Sorry, its in A mode. Q2105 is soldered to the darn board I will try to get readings on it but will they work being attached?

Yes, you can check the transistor junctions in-circuit using your DMM's diode check function.


Ok, I am trying to get back there.


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 7:13 am 
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tbone8 wrote:
stevebyan wrote:
tbone8 wrote:
Sorry, its in A mode. Q2105 is soldered to the darn board I will try to get readings on it but will they work being attached?

Yes, you can check the transistor junctions in-circuit using your DMM's diode check function.


Ok, I am trying to get back there.


Ok B-E was 1.57V and B-C was .683V, so that transistor is bad?! :D


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 7:24 am 
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tbone8 wrote:
Ok B-E was 1.57V and B-C was .683V, so that transistor is bad?! :D

Looks that way, but let's check the voltages on the base, emitter, and collector to be sure.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 7:40 am 
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stevebyan wrote:
tbone8 wrote:
Ok B-E was 1.57V and B-C was .683V, so that transistor is bad?! :D

Looks that way, but let's check the voltages on the base, emitter, and collector to be sure.


Ok, B+ to E- 1.57V
B- to E+ 1.57V
B+ to C- .832V
B- to C+ OL
C- to E+ .832V
C+ to E- OL

Bad right? If so, that one rascal is doing all this?


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 7:48 am 
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tbone8 wrote:
stevebyan wrote:
tbone8 wrote:
Ok B-E was 1.57V and B-C was .683V, so that transistor is bad?! :D

Looks that way, but let's check the voltages on the base, emitter, and collector to be sure.


Ok, B+ to E- 1.57V
B- to E+ 1.57V
B+ to C- .832V
B- to C+ OL
C- to E+ .832V
C+ to E- OL

Bad right? If so, that one rascal is doing all this?

No, I mean power up the scope and check the DC voltages with respect to ground.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 7:51 am 
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stevebyan wrote:
No, I mean power up the scope and check the DC voltages with respect to ground.


Ok, that will be a little tricky.


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 7:56 am 
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Base .000V
Emitter -7.95V
Collector .038V


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 2:12 pm 
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Yep, that transistor is toast. It's just being used as a switch, so just about anything should work as a replacement. Try a 2N3904 or a 2N2222 or a 2N4401.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 10:38 pm 
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stevebyan wrote:
Yep, that transistor is toast. It's just being used as a switch, so just about anything should work as a replacement. Try a 2N3904 or a 2N2222 or a 2N4401.


I obviously have to pull the darn board to change this out, do the two little wires going to the CRT just pull off? I will dig up a transistor and hopefully have it done this evening.


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 10:46 pm 
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While you have the board out, lift one end of one of the 47 ohm resistors (such as R2328) to open the bias loop, and measure all the resistances in the bias feed to pins 2 and 3. There may be some reason why the transistor failed.

Check R2103 and R2104 in Q2105's base circuit, too.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 10:58 pm 
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stevebyan wrote:
While you have the board out, lift one end of one of the 47 ohm resistors (such as R2328) to open the bias loop, and measure all the resistances in the bias feed to pins 2 and 3. There may be some reason why the transistor failed.

Check R2103 and R2104 in Q2105's base circuit, too.


OK :D


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sun 03, 2016 12:10 am 
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stevebyan wrote:
While you have the board out, lift one end of one of the 47 ohm resistors (such as R2328) to open the bias loop, and measure all the resistances in the bias feed to pins 2 and 3. There may be some reason why the transistor failed.

Check R2103 and R2104 in Q2105's base circuit, too.


I lifted one end of R2328 and the resistance between 2 and 3 is 30.6Ω. R2103 and R2104 are right on the money. I have a pirated 2N3904 transistor ready to solder in if you give me the thumbs up :) .


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sun 03, 2016 1:00 am 
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I decided to check all the resistors on the left half of the board, 3 were off, R2323 67Ω, is that off enough from 75Ω to be an issue? The other 2 are off by half.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sun 03, 2016 4:38 am 
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tbone8 wrote:
I decided to check all the resistors on the left half of the board, 3 were off, R2323 67Ω, is that off enough from 75Ω to be an issue? The other 2 are off by half.

They are probably OK. You'd need to check those out of circuit to avoid parallel paths that reduce the total resistance.

The resistance between pins 2 and 3 of U2225 seems rather low to me, but I'm not a good enough circuit designer to have any valid intuition. I'd replace the transistor and give it a try.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sun 03, 2016 5:48 am 
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You guys are geniuses!!!

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sun 03, 2016 6:11 am 
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Glad it's showing signs of life. It was a fun puzzle! Thanks!

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sun 03, 2016 6:20 am 
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stevebyan wrote:
Glad it's showing signs of life. It was a fun puzzle! Thanks!


Thank you! That is what I love to do is figure stuff out. In this case obviously I didn't do much of the figuring but I did learn a bunch. I can't believe you guys were so patient with me, very cool. I am probably too old to ever be a wiz at this but I sure am gonna try... :D


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