Date   
Re: Clearing error log in THS720A

 

On Sun, Oct 21, 2018 at 10:29 PM, zenith5106 wrote:


If you connect a PC running a terminal program to the serial port of the THS
you can try sending first PASSWORD PITBULL and then ERRLOG CLEAR.
Thanks a lot, Håkan.
Will try that during the coming week and share result.

Raymond

TEK 475 Q1478 2n5859

piodelreal@...
 

hello to all, i can´t find the part 2n5859 here in Mexico, this part number is critical in the -15v regulator performance or permits substitution ? any possible subtitutes?

any help will be really appreciated.

best regards.

Pio

2247A PSU Troubleshooting

Nicholas Keller
 

Hello, first post here and first real scope. A tech friend of mine gave me this in broken condition and said I could keep it if I can fix it. So here goes....

It doesn’t boot. Nothing happens when I turn it on.

I have disassembled the unit and visually inspected the PSU board as he said it had been repaired once before and was likely the same fault. He can’t find the service record. I couldn’t tell that anything had been replaced, and couldn’t see any obviously bad parts (swollen, leaking caps, for example).

I reassembled and powered up to test the power headers on the underside of the unit. They are all basically dead, however I did measure some mV on one of the high voltage pins.

I have a PDF of the schematic. I saw mentioned in a previous post about a record of some common issues with this PSU, but I couldn’t find the old post detailing these. Can anyone give me some suggestions before I attempt to trace signals? Is it safe to remove the PSU board and apply power to it even though some connections appear to be via other boards?

Thanks so much,
Nick

2465B vertical shift problem

ppppenguin
 

When I move channels 1 or 2 down the screen the trace is compressed at the bottom. As if the gain near the bottom the screen is about half that at the top. The effect is identical on both channels. Channels 3 and 4 are OK. Channel 2 output is OK. This looks horribly like U400 is in trouble and I've heard these hybrids are unobtanium.

I'd like to look at the differential outputs of U100 and U200 (and U300 for that matter, simply for comparison) where they feed into U400 in case there's a silly amount of common mode offset which might be causing the problem. But I can't see anywhere on the topside that I can probe. Getting at the underside looks tricky.

I've checked the power going to U100/U200. The +5V, +6.2V, -15V, -8V and -5V rails all seem to be within 2% of nominal.

I've looked at this article which isn't 100% relevant but illustrates an interesting fault and showing that U400 isn't always to blame: http://worldphaco.com/uploads/TEKTRONIX_2465B_OSCILLOSCOPE_MAIN_BOARD_INTER-TRACK_LEAKAGE..pdf

Your help, wisdom and advice would be very welcome. Even if it's only to say that U400 has definitely failed and the getting a replacement is well nigh impossible.

475 Z-Axis Amp Woes

agwnorden@...
 

Dear TekScopes

Could someone a bit more competent than me help with analysing the problem I am having with the Z-Axis Amp on my beloved 475 which has served me incredibly well for over 10 years.

The initial symptom was no trace. All power voltages and ripple were fine.

Using the XY setting to debug, I found the following. A spot will only appear in XY mode when Beam Finder (BF) is activated. BF, as I understand it, overrides the Z-Axis amp and sets the Amp O/P to about 25 Volts (from 6V) which then goes into the DC Restorer. Voltages at TP1364 confirm this works OK. (please see CRT circuit and Z Axis Amp circuits attached; apologies for quality but the best I have). This is also confirmed by simply putting -8V on the junction of R1342 and R1346; the spot reappears. X and Y position controls work fine with BF on.

The operation of the Z-Amp is described as follows in the manual:-

Z-Axis Amplifier
The Z-Axis Amplifier circuit controls the CRT intensity level from several inputs. The effect of these input signals is to either increase or decrease the trace intensity, or to completely blank portions of the display. The input transistor Q1338 is a current-driven, low input impedance amplifier. It provides termination for the input signals as well as isolation between the input signals and the following stages. The current signals from the various control sources are connected to the-emitter of Q1338 and the algebraic sum of the signals determines the collector conduction level.

Q1344, Q1352, Q1354, Q1358, and Q1362 compose a feedback amplifier stage. R 1369 is the feedback element, C 1352 provides high-frequency compensation. Q1344 is an emitter follower that provides drive to the output complementary amplifier made up of Q1352, Q1354, and Q1358. Q1358 is a device with higher frequency characteristics than Q1354 and is used to improve the overall frequency capabilities of the Z-Axis Amplifier. On the fast positive going output signal peaks, Q1358 depletes the charge on C1358. Then, on the negative-going signal peaks, Q1362 is pulsed on to renew the charge on C1358. CR 1367 provides protection to the Z-Axis Amplifier circuitry in the event of short duration arcing in the CRT High-Voltage Power Supplies.

My problem is, I think, that I do not really understand the circuit! When I rotate Beam Intensity I see no change in the voltage on the emitter of Q1338 (even with all other inputs (Q1332 etc.) disconnected. The voltages on Q1338 are Ve -2.498, Vb -1.729 and Vc 0.467 so Vbe is ~0.75 forward biaseed. Perhaps this always pulls Ve down when the Intensity Control is changed? Voltage measurements perhaps of little use in a summing amp like this?

If CR1341 is lifted as per the troubleshooting instructions below I do get the specified change in Vc of Q1338 which swings from +7.8 volts to –1.3 volts while turning INTENSITY control from full counterclockwise to full clockwise

Troubleshooting the Z-AXIS Circuit (CRT Circuit). Set TIME/DIV to 1 ms (lock knobs) and set TRIG MODE to SINGL SWP. Disconnect and lift one end of CR1343. Check the voltage at TP1364 for approximately +6 volts (OK). Press the BEAM FINDER pushbutton and check the voltage at TP1364 for approximately +25 volts (OK). If these voltages cannot be obtained, check the voltage across VR1362 for approximately +6.2 volts. Remove Q1362 from its socket and check the voltage at the base of Q1352 for approximately +1.3 volts. Check the base of Q1344 for approximately +0.6 volt.

If the above-mentioned voltages can be obtained, disconnect and lift one end of CR1341. Check the voltage swing at the collector of Q1338 for approximately +7.8 volts to –1.3 volts while turning INTENSITY control from full counterclockwise to full clockwise. (OK). If these voltages cannot be obtained, check the voltage at the base of Q1338 for –1.75 volts. Remove Q1332 from its socket.
Disconnect J1333 and J1334 (coaxial-type end-lead connectors) from their sockets. Repeat the voltage swing check at the collector of Q1338 as performed previously. Connect J1333, J1334, R1343 and CR1341 to the circuit board. Install Q1362 and Q1332 in their sockets.

Replacing all parts and confirming initial voltages around Q1338 I see no response to the Intensity Control at Ve of Q1344, the emitter-follower driving the Z Amp. That is surely wrong?

This places the fault around Q1338/1344 but I cannot find a problem. Junctions of the two test OK. The only obvious fault about the board is some discolouration of CR1360 but it still rectifies.

I apologise for the density of this email but any help much appreciated. I have no more hair to tear out.

Anthony M0WWV

Re: 2465B vertical shift problem

Chuck Harris
 

Don't condemn the vertical hybrid just yet. First,
check that you have all of the proper power supply
voltages at U119 on the motherboard (see manual).
Next, check for a bad connection to the pins coming
out of the side of the CRT for the vertical deflection
plates, both at the output of the amplifier, and at
the termination circuit board.

Be warned that shorting either deflection pin to the
CRT's mumetal shield will instantly destroy the hybrid.

Avoid bending the pins close to the glass seal. They
are very thin pieces of wire.

I have the hybrids if you find you really need one.

-Chuck Harris

ppppenguin wrote:

When I move channels 1 or 2 down the screen the trace is compressed at the bottom. As if the gain near the bottom the screen is about half that at the top. The effect is identical on both channels. Channels 3 and 4 are OK. Channel 2 output is OK. This looks horribly like U400 is in trouble and I've heard these hybrids are unobtanium.

I'd like to look at the differential outputs of U100 and U200 (and U300 for that matter, simply for comparison) where they feed into U400 in case there's a silly amount of common mode offset which might be causing the problem. But I can't see anywhere on the topside that I can probe. Getting at the underside looks tricky.

I've checked the power going to U100/U200. The +5V, +6.2V, -15V, -8V and -5V rails all seem to be within 2% of nominal.

I've looked at this article which isn't 100% relevant but illustrates an interesting fault and showing that U400 isn't always to blame: http://worldphaco.com/uploads/TEKTRONIX_2465B_OSCILLOSCOPE_MAIN_BOARD_INTER-TRACK_LEAKAGE..pdf

Your help, wisdom and advice would be very welcome. Even if it's only to say that U400 has definitely failed and the getting a replacement is well nigh impossible.

Re: 2465B vertical shift problem

ppppenguin
 

Chuck, thanks for the advice. I swapped U400 with one from a 2465 and that fixed the problem. One day I may try to fix the 2465 but it has a stubborn intermittent that I've never managed to fix. So I suppose it's now a parts donor.

Good to know that you have the hybrids available if i really need one.

Re: A (safer) way to look at the mains.....

Dale H. Cook
 

At 10:15 PM 10/20/2018, Dale Chayes wrote:

When I have to do this, I used to start with a 10:1 transformer
For decades I have looked at mains noise and distortion with a Beckman CT232 AC current clamp. It has a bandwidth of 30 Hz - 10 kHz and a range of 1-1000A. Its output is in ma per volt. I use it to feed a 'scope to look at the AC waveform, especially when looking for spikes, or to feed an HP 334A distortion analyzer to measure mains distortion and noise. Of source, it can also be plugged into a DMM or AMM to simply measure current.

Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcity/radios/index.html

TDS 3014 TDS 3000 scope Strange display "System Error " report, on BootUp, ... with no effect on scope function: repair of, or Clearing / Reset this Error Log ?

garp66
 

Tek TDS 3014 scope Boots up & passes all 8 self-tests , but reports a "System Error" in the Graphics System:
( The BootUp Self-Test passes everything, including 'Application modules' -- even though there are none inserted in the two upper right module compartments)

This scope *functions correctly* for all four channels, over its frequency & amplitude ranges.

screen#1:
"System Error
A System Error has Occurred.
Contact your Tektronix Service Center for Assistance."
...

screen#2:
" Number of Power Ups 179
Diagnostic Results:
Acquisition PASS
CPU PASS
Display PASS
Front Pannel PASS
I/O PASS
ROM PASS
Disk Drive PASS
Application Modules PASS"

screen #3:
" Number of Power ups 179
Total Operating time 15753532 hrs.
System Errors 783
Breakdown by Sub System:

Acquisition: 0 CPU: 0 Display: 783 ROM: 0
Front Pannel: 0 I/O: 0 Disk Drive: 0

179: 21 0 34 Graphics 120:80:4140/120/ 0 "

Interesting:
a) Nothing mentioned in the screen#3 diagnostic about Application Modules.
b) The # of Runtime hours is way-off *anything* reasonable = > thousands of years (millions of hrs.);
would have 1st turned on ~ 1798 yrs. ago ! (not possible !)

Wondering if :
1) there might be a Boot up RAM or NVram battery (in the display section) that has gone south, providing faulty parameters ?
2) Missing Application Modules (compartments all empty) but retained Lic Codes previously transferred to the TDS 3014 by previous users ; causing the soft error ?
3) Runtime hours (millions) are completely unrealistic; only ~ 8760 hrs in a year !
4) Meaning of the System Diagnostic code: 179: 21 0 34 Graphics 120:80:4140/120/ 0 ??

-- Any way to do a 'hard reset' to cure this error ?
-- Any replacement Nvram battery possible, wherever that is ? ?
-- How to remove any Lic Code for a non-existent Application Module(s) { Or method of transfer it back to the Application Modules, if modules found ) ?

Other actual solutions ?

thanks,

Re: TDS 3014 TDS 3000 scope Strange display "System Error " report, on BootUp, ... with no effect on scope function: repair of, or Clearing / Reset this Error Log ?

 

On Mon, Oct 22, 2018 at 07:34 PM, garp66 wrote:


1) there might be a Boot up RAM or NVram battery (in the display section) that
has gone south, providing faulty parameters ?

-- Any replacement Nvram battery possible, wherever that is ? ?
There is a DALLAS DS1742W-150 Timekeeping RAM that might or might not be the problem.
Some time ago I had a TDS 3014B that got stuck on the flash screen. Fortunately I had
a scrapped main board from another TDS 3000 and as last resort before scrapping it I
took the DALLAS chip from the scrapped board and installed in the scope. Much to my
surprise it solved the problem so it could be worth replacing yours.

Another thing to watch out for is the F/W version. There was one version that
could mess up the NVRAM quite good due to some memory address issues. It was v3.12.

/Håkan

Re: 2247A PSU Troubleshooting

 

On Mon, Oct 22, 2018 at 03:22 PM, <Nirokeforums@...> wrote:


It doesn’t boot. Nothing happens when I turn it on.



I reassembled and powered up to test the power headers on the underside of the unit. They are all basically dead, however I did measure some mV on one of the high voltage pins.
Did you check the mains fuse and switch?

Raymond

Re: 2247A PSU Troubleshooting

Nicholas Keller
 

Fuse: yes.

Switch: no, and I should have because that’s an easy one and have had bad
switches on other gear

Thanks, Raymond, I will check the switch tonight after work

Nick



On Mon, Oct 22, 2018 at 10:14 PM Raymond Domp Frank <@Raymond>
wrote:

On Mon, Oct 22, 2018 at 03:22 PM, <Nirokeforums@...> wrote:


It doesn’t boot. Nothing happens when I turn it on.



I reassembled and powered up to test the power headers on the underside
of the unit. They are all basically dead, however I did measure some mV on
one of the high voltage pins.
Did you check the mains fuse and switch?

Raymond



Re: TEK 475 Q1478 2n5859

Chris Wilkson
 

Is it in a TO-39 (metal) case?
Try findchips.com. Several sources to choose from, though Mouser is out of stock.

Re: TEK 475 Q1478 2n5859

piodelreal@...
 

Yes it is TO-39, thank you

Best regards.

Pio

Re: 2445A calibration

maxim.vlasov@...
 

Just wanted to ask your advice,

On the local auction someone put 2445a (exactly the same like mine) for the bargain price - 100 USD delivered. I wonder whether this is worth buying. Apart from a missing knob, the scope is an a good working order and calibration seems valid (no question marks at least). The seller seem to know about how to test the scope, since he put a picture with multiple traces showing different signals. Screen seems bright, sharp and not distorted.
I wonder, would you buy one more (even if you haven't planned this) for such a price?

P.S. If this auction would appear 2 weeks before, I would likely ditch mine that time, since the effort seem to be almost unfeasible.

Re: 2445A calibration

John Ferguson
 

After seeing a tip here on a 2465 for sale for $50 plus shipping, I bought it.  It was advertised as having a bad horizontal switch - it had been dropped on it.  Well they were right, it was bad.  I was able to get a replacement panel for it complete with all the controls for $37 IIRC.  Now it works great.  A few years back I bought a 2445B on which everything worked except the parametric functions.  I thought it would be good to buy another 2445B for parts. When it came, everything on it worked except Channel 1 which was very noisy - turned out to have a fried attentuator.

At this point, I decided it might be good to have one of them calibrated.  I sent the one needing a new attenuator to one of our members who does this sort of thing, and had the PS recapped, the A-5 Board smt caps replaced and the NVRAM replaced with a socket and a FRAM. It came back really nice with a great trace and everything working. I now have a certain to be good 2445b, a 2445b which can be used manually and seems pretty good, and the 2465 which also seems ok.

This is nuts.

I need to get rid of at least one of these, but can't bring myself to part with them.

john

On 10/23/18 3:49 PM, maxim.vlasov@... wrote:
Just wanted to ask your advice,

On the local auction someone put 2445a (exactly the same like mine) for the bargain price - 100 USD delivered. I wonder whether this is worth buying. Apart from a missing knob, the scope is an a good working order and calibration seems valid (no question marks at least). The seller seem to know about how to test the scope, since he put a picture with multiple traces showing different signals. Screen seems bright, sharp and not distorted.
I wonder, would you buy one more (even if you haven't planned this) for such a price?

P.S. If this auction would appear 2 weeks before, I would likely ditch mine that time, since the effort seem to be almost unfeasible.


Re: 2445A calibration

maxim.vlasov@...
 

On Tue, Oct 23, 2018 at 01:11 PM, John Ferguson wrote:


This is nuts.
Thank you John,

For me also it's difficult to walk by this advertised 2445a, especially, since it seems like it has nothing broken at all...
And for many things including the phase measurements the analog scopes are still my preferred choice (XY mode on the recent digital machines is more of a gimmick).

Re: 2247A PSU Troubleshooting

tekscopegroup@...
 

I have a 2247A myself, excellent GP scope.

One of the first recommended things to do I was told is replace all the rectifier diodes in the A18 LV power supply that have ZM or ZS markings on them as they are well known to get leaky after "some time" (quoting the very knowledgeable person that sent me this recommendation). Replace these diodes with MUR160 600V 1Amp, you easily get them at Mouser, Digikey, etc. On my scope all of them had either of the above suspect markings, so just to be safe I replaced all of them. Whole procedure takes maybe an hour or two, your mileage may vary.

Of course for an instrument this age, needless to mention to also check filter caps, specially if you see higher than normal ripple on any of the supply rails.

Suspect diodes are Tek PN 152-0400-00 (total 17 diodes) with alternate PN given as MB2501. These are the on-board part locator numbers:
-CR2202
-CR2204
-CR2205
-CR2208
-CR2209
-CR2210
-CR2211
-CR2212
-CR2213
-CR2214
-CR2215
-CR2216
-CR2218
-CR2227
-CR2228
-CR2235
-CR2236

Hope that helps.
Alex

475 Probe Calibration problem with x10 probes

n2msqrp
 

I have two 475 scopes. Both have developed a similar probe calibration problem on one channel. I am using the scope calibration signal. I have verified results with multiple probes

First scope - Channel 1 probe calibration tests fine with x1 and x10 probles. Channel 2 calibration tests fine with a x1 probe but the waveform has a sloped rise and fall time when testing with a x10 probe on a vertical sensitivity setting of .5v/div and above.

Second scope - Channel 1 probe calibration tests fine with x1 probes but the waveform is a spike when testing with a x10 probe with vertical sensitivity setting of .5v/div and above. Channel 2 probe calibration works fine with x1 and x10 probes.

Has anyone seen this problem?

Mike N2MS

Re: 2247A PSU Troubleshooting

Nicholas Keller
 

Thank you, Alex. This must have been the suggestion I saw here not too
long ago, I just got the impression that the diode list was an abridged
tally of what “should” be checked and replaced. When I pull the board
again, I will check these diode markings. Unfortunately I can’t test for
ripple yet as there is no power getting to the supply rails. I’ll report
back when I’m able to make some progress. Thanks again!

Nick

On Tue, Oct 23, 2018 at 8:09 PM <tekscopegroup@...> wrote:

I have a 2247A myself, excellent GP scope.

One of the first recommended things to do I was told is replace all the
rectifier diodes in the A18 LV power supply that have ZM or ZS markings on
them as they are well known to get leaky after "some time" (quoting the
very knowledgeable person that sent me this recommendation). Replace these
diodes with MUR160 600V 1Amp, you easily get them at Mouser, Digikey, etc.
On my scope all of them had either of the above suspect markings, so just
to be safe I replaced all of them. Whole procedure takes maybe an hour or
two, your mileage may vary.

Of course for an instrument this age, needless to mention to also check
filter caps, specially if you see higher than normal ripple on any of the
supply rails.

Suspect diodes are Tek PN 152-0400-00 (total 17 diodes) with alternate PN
given as MB2501. These are the on-board part locator numbers:
-CR2202
-CR2204
-CR2205
-CR2208
-CR2209
-CR2210
-CR2211
-CR2212
-CR2213
-CR2214
-CR2215
-CR2216
-CR2218
-CR2227
-CR2228
-CR2235
-CR2236

Hope that helps.
Alex