TekScopes@groups.io

Re: Tek 465 no display

The +, +5 and -8 are all referenced from the +55 volt line. One of them can short it out, but if it is gone, they are gone.

Re: Tek 465 no display

#149232

On Wed, Jun 20, 2018 at 04:33 pm, musicamex wrote:

My sn is B 317000. But i am not having much luck in finding the downloads for
this later version.
The one on this page says SN B 250000 and up 

I can't give you the exact URL because I had to "upgrade" my browser and now instead of just saving the file it insists on displaying it. Another function I used GONE. 

But it says 465.pdf, noting else. Then there are some other versions, M, B whatever. But I got the one and it does say 250000 and up.

Re: Dead 7603

#149231

On Mon, Jun 25, 2018 at 10:37 pm, Craig Sawyers wrote:

THEN YOU SHORT THE EXPOSED TIP OF THE CRT WIRE TO GROUND
Sorry, I didn't take that as meaning the lead from the CRT, I thought you meant the lead out of the multiplier. 

Doing that after it is powered up and down, if it has an arc you have cleared the CRT and the multiplier, but don't yet know which one is bad if it doesn't. 

So you didn't say to turn it on and arc the anode lead (output of the multiplier) to ground. This appears to be my mistake. You probably agree that it is not a good idea to arc the source while running to ground, but you never said that it was. 

I'm sorry, it's my mistake.

Re: Tek 465 no display

#149230

Hi Fabio,

Thank you so very much for this information!  I will make some time tomorrow afternoon to put this all to use, or to the test in the real and figurative sense.  I have been truly bewildered by the complexity of this circuit and the high probability that anything that I need will have to be part of my early October trip to the states.  Although I  have an inventory to repair 95% of all tube amps that find their way here, I dont have much at all for this attempt.  Tube amps are so logical and similar that they might have given me a false sense of my abilities.   But I am determined not to relegate this highly regarded and clean 465 to the bone yard.
I was feeling like I was lost in a big city without a map and with your pinpoint instructions I hope to start to find my way.

For some reason 3 of my posts never showed up here. It might be my cobbled together internet connection.  I live about 4 km outside of our town and there was no internet at all before.  And marginal cell service on top of a nearby hill.  I rigged a few solutions, but now that we are in the monsoon season it can have its challenges.  One attempted post had some measurements including voltages on the main filters. I'll pull out my notes and try to repost along with the results of the suggestions and guidance you just gave.

Thank you again. Russ

Btw, I just bought a TDS 460A with a "passed self test" screen.  I want to have at least 1 working scope for each 2 work station bench and one for me to demo with.  I probably should stick with analog scopes from the same family like my 465 and 485, but I  was browsing ebay late one night recently and the 460a popped up with minutes to go .  I had a GAS attack and shot a low bid and got it.  I just know it will get me additional scrutiny as my carryon just like the last 2.  At least this one is lighter?

Re: Dead 7603

#149229

On Mon, Jun 25, 2018 at 09:38 pm, lop pol wrote:

Ok. You can't just leave it there. How do you discharge the CRT? ?\_(ツ)_/?
When dag was no longer ground in TVs we used a HV probe, usually 1090 meg which with the meter made 1100 meg. 

But the capacitance, (Leyden jar) is to ground, not the cathode. With  it OFF you can just arc it. It is a problem when you do it when on. When you short the ON "top" (+) HV to ground the "bottom" of that transformer winding shifts all its voltage to the cathode circuit. 

It has a quadrupler, that means the 3 KV on the cathode end is simply rectified, but quadrupled into the + so0urce for the ultor. If the + shorts that will cause double the voltage to the cathode circuit. That is just about the right amount to blow a bunch of shit before the rectifier or filter shorts out. 

I am not looking right now but many Teks have a shunt regulator tube for the cathode end, if you burn that out, where do you get one ?

I have worked on some damn expensive equipment and have learned to be careful. Had some sort of car diagnostic machine once, them people will work on anything, or actually have me do it. no red. the other guy, normally competent, decided to rejuv the CRT. I said no. they did it anyway and still no red. I had to go to the video subsystem of a computer and find a bad gate IC. then we got red, but not the formally pristine cathode has now been stripped so guess which gun is going to go first. 

I INVENTED the dim bulb test., I do not claim to have invented it first, but when I figured it out I had never heard of one. It was house wiring, a fuse kept blowing. I screwed a light bulb into the fuse socket and it lit and I started disconnecting things until it went out. Non destructive testing. You don't want to know my age but, I hadn't yet gotten my first hardon. 

Point is, destructive testing is only for when it  is absolutely necessary.

Re: Tek 465 no display

#149228

Hello Russ,
I've already suggested some vague, not quite specific, approaches... and then kept following this topic from a distance for a few days to see if someone with more specific knowledge on the 465 would jump in, but it seems there's silence on the radio for a while.
Maybe everybody is expecting you to produce some more information with the hints you already got, and maybe you're waiting to be "taken by the hand" a little bit further before proceeding... so this is stalling.
I`m not particularly experienced with the 465. I have a 464, whose Low Voltage Power Supplies (hereby on, just LV, or LVPS) are quite similar to the 465, so I hope this will suffice.
By looking at the name of the test points you reported earlier, I assume that I`m looking to the same schematics that you have but, to avoid further misunderstandings, I`m looking at the manual whose part number is 070-1861-00 (written on the lower left side of the cover) which states "SN B250000 & UP".
When I mentioned the current sense resistor on my previous post (message #149051), I was talking about R1549, of 1.1 Ohm and, answering to your question, no it's not individual to each tantalum capacitor.
The voltage drop on this resistor, when exceeded a given amount of current, turns on the fold-back current limiting transistor (Q1548, R1456 and R1457) which steals away bias from the +15V pass transistor, Q1546.
So, from several things that may cause the voltage of the +15 LVPS to be zero, one of them could be the +15V shorted to ground.
From all possible causes for the +15V to be shorted to ground, the various dipped tantalum decoupling capacitors are the most common causes, almost a chronic disease on scopes of this vintage. *** dipped = a radial tantalum capacitor that looks like a color striped epoxy blob, not the more rare wet tantalum that looks like a metallic cylinder with axial terminals.
Only to serve you as an example, it can be C1559, right on the +15V output, or C1339 on diagram 8 (SWEEP & Z AXIS LOGIC) connected to the +15V via a 22R resistor, or C891 on diagram 5 (A & B TRIGGER GENARATORS) conneted to the +15V via a 2.7uH inductor, or C4498 on diagram 4 (VERTICAL OUTPUT AMPLIFIER, discrete version) connected to the +15V via L4498//R4498, or C346 or C358, both on diagram 3 (VERTICAL SWITCHING), etc, etc...
What sucks about finding shorted decoupling capacitors is that they're - sort of - all in parallel, and if one is shorted, it takes the whole rail down.
Of course, some of them can be ruled out right away, like C1339 above, which is not connected directly to the +15V, but through a resistor, and in that case, it wouldn't be able to short the rail down to an absolute 0V like you measured.
As a matter of fact, for the +15V to be reading a dead zero volt (as you measured), it's unlikely the problem to be a shorted tantalum alone (because the voltage drop on the PCB's copper tracks, plugs and connectors, would make some small voltage to be present at the +15V TP),
But a shorted tantalum may have caused something else to burn open, and in that case, you may be looking at two problems, and not just one.
Measuring the voltage drop at R1549 (the current sense resistor) is a good way to see if the +15V supply is sourcing any current (which may be shorted to ground) or if it's sourcing no current at all, or if R1549 is open altogether.
If you measure a very low voltage (say < 0.1 V) across this resistor, probably the +15V power supply itself has a problem (an opened pass transistor Q1546, or lack of drive from U1524B) which will need to be troubleshoot further.
If you measure something between 0.7V and 1V, then it means the +15V power supply is trying to source its juice, but it's being turned down by the over-current protection (an indication of a short circuit downstream).
Finally, if you measure a higher voltage across this resistor, maybe up to the full unregulated voltage (say 24V), it may be R1549 itself open.
You can probe a few things to help troubleshoot further:
1. Voltage across R1549 for a starter.
2. Voltage (in relation to ground) at pin 8 of U1524B. There must be 22V there. Lack of such and the +15V will fail.
3. Voltage at pin 5 of U1524B must be a 15/55th proportion of the +55V power supply (at the current state of affairs, it must be at 12.79).
4. Voltage at pin 6 of U1524B must be whatever voltage you're measuring at TP1548, in other words, it should be reflecting the actual +15V PS voltage.
5. If all voltages at topics 2, 3 and 4 above check, then the OpAmp should be at full thrust. i.e. anything from around 2.4V (the sum of Vbe of Q1544 + Q1546 + Voltade drop on R1549) up to about 21V (whatever volttage is at pin 8 (the IC + supply pin) minus 1V.
6. Voltage at the collector of Q1544 and Q1546 must be the same as the +15V UNREG voltage. As per your very preliminary messages, this should be at about 24.5V (it's the voltage that you measured on both sides of the internal fuse, F1419, which is fed from the same voltage.
*** There's a missing piece of information on the schematics... The +15V UNREG voltage that feeds the high voltage inverter IS INDEED, the voltage that is going into the +15V PS regulator (the collectors of Q1544 and Q1546), but this information is not mentioned anywhere in the PS diagram.
From the 6 measurements above, you will be able to draw a conclusion, or report back and someone here surely will.

KRgrds,

Fabio

Show quoted text

On Sat, Jun 23, 2018 at 08:52 pm, musicamex wrote:


Harvey, Thanks for your reply.  I referred to the manual suggested here by
other members, 465 Late, as my sn is the later model.  On pg 215 and for the
next several pages it explains (to someone with more savy than I have re these
circuits) troubleshooting the lv circuits.  All voltages seems dependent on
the 55v working properly.  I wonder if I need to first bump the 55v up from
its out of spec 46.9v first?  I have very limited experience with transistors
and their proper function in this circuit.  But i  did notice most seem to be
plug and play connections  instead of soldered like l am familiar with in old
tube amps.  That makes the plug in 40ish yr old connections throughout this
scope suspect imho.  I hope I'm wrong.

Any coaching with specific instructions for a guy with a pretty well equipped
lab but limited sources here in Mexico for technical help.  In the late 60's I
was able to fix a Perkin Elemer Atomic Absorption Spectrophotometer in a lab I
ran in Alaska with phone coaching from PE saving perhaps months of down time
during a very short productive prospecting season.  I have much better repair
tools than I did then, so l am confident with the diagnostic veterans here
helping, that i can get this otherwise  clean old scope working again.

Thx, Russ

MEDIA MAIL (Re: [TekScopes] I have two Tek manuals I don't think I need)

#149227

They are trained NOT to tell you. You have to ASK for it or as the previous poster said it is available through PayPal shipping includes tracking. Tell them it just a "manuscript" and DO NOT INCLUDE any correspondence. You put a one page letter in there and suddenly it is a 1st class mail

For a description google is your friend

-DC
ArtekManuals.com

Show quoted text

On 6/26/2018 1:40 PM, John Griessen wrote:
On 06/26/2018 11:26 AM, David Berlind wrote:
what is "media mail?"? when I go to the post office, they offer me a slew
of options.. but "media mail" is not one of them.use paypal shipnow to get a label for media mail with a little extra discount.

-- 
Dave
Manuals@...
www.ArtekManuals.com

Re: Opinion on tds 460a

#149226

Congrats on your new TDS460A. Sounds like a bargain.

As far as whether a late-90s unit will be free from the capacitor issue, I can only say that my TDS460 (not "A"), with a build date of Nov, 1992, had the capacitor leakage problem. Some traces on the ACQ board were in rough shape, but it was possible to clean, repair, and recap it without too much bother. 

If your caps have not leaked, it is pretty easy to remove them and replace them. Once they have leaked, things get trickier. It might be worth doing the replacements now; IIRC the cost for a complete set of new Nichicon caps from Mouser was less than $30.

A couple of other repairs were needed on my scope; they might or might not be something that could show up on your '460A. First, one of the electrolytic caps in the housekeeping supply section of the main switcher went open circuit (no leakage, interestingly enough). This made a couple of the negative supply outputs to go way out of tolerance. An easy fix, as it turned out.

The other issue was that the optocoupler used in the soft power ON/OFF control if the switching power supply degraded to the point that it was apparently trickling charge into the base of its output transistor, so that the coupler never really turned off all the way. That was reflected in erratic behavior of the front panel PWR pushbutton. Another easy fix, after which the scope settled into working reliably.

BTW, I put my TDS460 on eBay a couple of days ago as part of a lab clean-out effort. It is listed with Best Offer enabled, and I would be please to extend a TekScopes discount if a member were interested (item 263779628201; please excuse the plug).