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If anyone is interested, just an update to say that the -15v problem is located on the A62 Video Amplifier board.

With that board removed the CRT and controls come back to life with crisp details.


Have to go to work now but shall see if it can't be fixed later.

Progress!

:)

Hi Dominic.

I'm in Brazil, and this this weighs more than the plane needed to fly it across the Atlantic.

Good luck though with your projects.

James

UPDATE: Fixed. Shorted rectifier, -15V supply.

Feel like I got a real bargain. $99, included shipping.

Hi James
Always interested in a repair project - am in Cheshire - so if you decide to part with the 492 then please let me know

Best regards

Dominic

I recently purchased a Tek 561A oscilloscope and determined that there is something wrong with the timebase plug-in. I followed the troubleshooting guide in the manual and determined that there is something wrong with the horizontal amplifier and the normal sweep generator (according to the test points for these parts of the plug-in the voltages are way out of spec) any insight onto what the issue would be would be greatly appreciated

Hello all

I just picked up a 2246 scope that won't power up.
Although I'm a very experienced tech, thought I would ask for any common SMPS faults before digging in further.

The +44VDC on primary side is OK.
Nothing on secondary side, except for short "blip" of voltages on outputs as it attempts to start up, then
of course, drops to zero.

The unit is absolutely spotless inside, doesn't look like its ever been used. (Cabinet exterior is also excellent)

Thanks in advance,
Mike

HI Teksperts
I have the chance of getting my hands on a TDS684A with a discoloured screen and suspect that it mat be suffering from the degradation of the 'gel' between the CRT and LCD 'shutter'?
I have discovered that there is a modification to replace the CRT and shutter with a backlight LCD panel.
Has anyone any experience doing this successfully and any pointers to the technique.
Secondly whilst scouring the web for this repair information, I also noticed that quite a few of these series of 'scopes can be 'hacked' to unleash the full power of the instrument.
i.e. faster and deeper memory etc. (throttled back at the factory)
Are there hacks for the TDS684A in a similar vain?
Finally the TDS684a is sometimes listed as a 500MHz machine and in other places a 1GHz instrument.
So....
What frequency will the instrument faithfully reproduce on screen please?
Thanks in anticipation
Dave

So,
reassembled and turned on, the unit fires up, or at least all lights and scale illumination light up, before leaving three led's and the scale illumination on, but nothing else. No response to anything.

Checking the voltage rails at the test points near the front left reveal that all are fine except the -15v which reads -1.5v

Honestly not sure about how much time to devote to this, although perhaps it's something as simple as bad electrolytics or tantalums?

Picked up a nice, functioning 7633 with the 7L13 Spectrum Analyzer plug-in for less than 10 British Pounds, so perhaps I should just pass this 492 along?

If anyone has any suggestions, please feel free...


James

Hi Bob and Mark,

Thanks for the feedback.

OK on PSU capping, might spend the dollars and give it a fresh start.

OK on 2 x 4 way ribbons, makes total sense. Just read storage board latch and analog isolation jumper process.

Regards

Gerald

Jurgen,

Since the fuses are blown, check the solid state devices in the power supply. Replacing the condensers in the power supply is a good idea. Use high temp, low ESR and long life types like NIchicon ULD, UHE, UCY and LGR (these would be for the 470mfd 200V types). Raising the capacitance and voltage is fine. See if any RIFAs are in there. If so, replace. There may be small ones, not only on the mains filtering from the power cord. Shorted tantalums are possible.

Mark

Hi all,
after a long time I switched on my 2784 and it was running for several minutes without CRT Image. Then the internal Fuse and the fuse of power outlet was blown. I think LED 10, 11 and 12 did not shine the first minutes
before the fuses were blown. Also the CRT gave no picture. Nothing to see on the pcb of the power supply. Will take a look on the HV supply and change the two 200V 470uF capacitors.
Perhaps anyone can give me a hint. I think, that it can be only a dry capacitor after 30 years. So the calibration has to wait, but I found the circuit diagram for the Processor Extender in this group.

闯ü谤驳别苍

Hi Gerald,

The PSU heat is dissipated, when in the case, by the screw through the case making a thermal connection to the outer case. Maybe not the best idea Tek had, but it works.

When you have the digital board in the service position have you connected the two 4-wire ribbon cables with jumpers? This is required, or the acquisition will not work correctly.

Best,

Bob

In that case... Excellent!

This thing was picked up very cheap at the flea market and have no idea as to it's history, however it does seem to be complete, so let's see what happens with the PSU working?

Thanks again.


James

James,

The neons are there to help discharge the condensers when it is turned off. When on, the limiting resistor makes the combination of the R and Ne a relaxation oscillator. These blinking when on is normal operation.

Mark

Aneesh,

Removing the ribbon connector while on could cause the IC to be defective causing a spike to damage the mosfet(s) in the upper part of the schematic. C807 could be shorted. Q802 could be bad making Q801 overheat. The 430 ohm resistor will need replacing. Both mosfets should be replaced after you find the problem. See if W17 is shorting to the shield.

Mark

Gerald,

Replacing the condensers in the power supply may make the temperature drop. The originals likely will be 85C. Nichicon UHE and UCY for the 100V supply are excellent replacements. Raising the voltage and capacitance is fine. The increase in voltage such as from 12V to 16V and 40V to 50V are examples.

Mark

Hi All,

I am in the process of alignment after an extensive repair process of a very clean 2232.

I have several questions, hopefully some answers:-

1. Does the rear right side, PSU section get quite hot, fan and air flow is not impeded and is working as intended, PSU voltage and ripple values work as documented, only -5.0 is sitting at -5.38 W9020?
2. Does anyone have a better understanding on the (13. adjust acquisition position offset (R7325 and R7335) when in test mode as documented on page 103 in section 5.10 of the SM?

The Digital card must be in the service position to gain access to R7235 and R7335, this may present some alignment issues and position(s) of on screen lines, but happy to be corrected on this?

Thank you in advance.

Regards

Gerald
VK3GM

Hi Jurgen,

If ok with you, let's take this offline for now.

Drop me a PM, any development can be shared in the future.

Regards

Gerald
VK3GM

Quick progress report;

..is that with the unit open on the bench, and with two 2SC4430's (the BUV48A's were overpriced in the shop) in place of the 151-0703-00's then the voltage rails are once again working. So that's great news!

Thanks to Mark and Albert for their help.

The only thing that stands out, is that the little neon next to the two large filter caps is lightly flickering away. I never had the unit open before but aren't those neons for circuit protection in the event of a fault?

James



It's late here now but tomorrow I'll assemble everything

Hi Albert.

If I was fairly confident that I had the correct pin-out, you've made me certain.

Many thanks