TDS-524A does not power up

[JVG]

Hi all,

Here I am again with a new project

After the unsuccessful (by now) CSA-8000 repair attempt, I have got a very nice looking TDS-524A with, apparently, a power supply problem. It does nothing when ON/STBY button is pressed. Of course, fuse is fine

Any hint to start troubleshooting?. Are these SMPSs fixable?

Regards,

JOSE

[cap]

Hello,

There is an on/off switch in the case, try that to rule out the front panel/flex cable. Often, the failure will be obvious on the power supply board, on occasion the large caps off the mains will fail, or one of the large clamping devices in the same area. Look for leaking electrolytic on the board. Same power supply as the TDS520/540/520A/540A/544A and 620/640/620A/640A/644A.

Replace ALL smd electrolytics prior to powering it on…

cap

[JVG]

Hi cap,

You seem to be in all threads. Thanks for your help !

Hello,

There is an on/off switch in the case, try that to rule out the front panel/flex cable. Often, the failure will be obvious on the power supply board, on occasion the large caps off the mains will fail, or one of the large clamping devices in the same area. Look for leaking electrolytic on the board. Same power supply as the TDS520/540/520A/540A/544A and 620/640/620A/640A/644A.

Replace ALL smd electrolytics prior to powering it on…

cap

Yes, the ON/OFF switch is OK. And when you connect the plug, there is the usual spark noise so the primary side seems OK.

I have removed the PS cover and there is nothing evidently damaged. In fact, the unit looks very clean , with just some slight dust.

About replacing all SMDs, I know it is a must once I get the PS doing something but, is it so important to do that BEFORE even getting the PS to work?. I mean, may be that the problem for non-start?. Visually the SMD caps look OK (well, I have had no time to check in great detail yet, but there was no obvious damage as I have seen in other Tek units, as the 2465B or 2430A). I will replace them, for sure, but I guess fixing the PS has higher priority. Am I completely wrong?

So, one question... are there some test points on the PS I could use?. I guess there is no detailed info / schematics of the PS, right?

Regards,

JOSE

[nctnico]

Did you try to disconnect the CRT unit? The internal power switch is the push button on the processor board.

Look for the TDS520B component service manual on this website. It has a diagram of the PSU. It looks complicated but the PSU is basically a forward converter with linear post regulators.

[JVG]

Hello nctnico,

Did you try to disconnect the CRT unit? The internal power switch is the push button on the processor board.

Look for the TDS520B component service manual on this website. It has a diagram of the PSU. It looks complicated but the PSU is basically a forward converter with linear post regulators.

No, have not done yet any test; I got the unit yesterday in the evening and was only able to take out the cover, look inside (to find a pretty impolute unit ) and then open it up to the PS area. That was all !

Yes, I have got the 520B manual (a God send!) and will study the PS and do some checks. I will also try disconnecting the CRT unit (it is easy to do, I guess)

I wonder if I can test the PS without the control board... There should be some info in the 520B manual but I have had not time yet to dig it out

Regards,

JOSE

[cap]

Just know that the original smd electrolytics are completely unreliable, and can wreck your scope. You can take your chances and luck out but I would replace them first, just a few hours of effort.

You could disconnect the acquisition board and work on the power supply and if you get life immediately turn it off and address the smd’s. The TDS520B components service manual has schematics; the power supply is similar to yours.

If your lucky, the power supply died early in life and the scope was simply set aside. Nice clean looking smd pads are a good sign, easier to work with and less likely to be at deaths door.

cap

[nctnico]

I must note that later scopes may not have the leaky capacitor problem. I have a TDS644A from around 1994 and a TDS510A from 1997. The TDS510A does not show any trace of leaky SMD capacitors. The TDS644A was another story. Every SMD capacitor was leaking. Someone here mentioned Tek has been reworking TDS500/600 scopes since around 1994.

[cap]

I have never seen a TDS510A. All of the other scopes definately had them, numerous 544A's and 540A's. Has allot to do with hours used, 520x/620x type scopes are often great sources of parts or for repair simply because the go unused if a more capable 540x/640x machine is availlable. But that depends on the resources availlable on a bench. If your scope was rarely turned on to begin with... But some are ran 24/7 until they stop.

I have had 544A's that ranged from shiny new looking cap/pads that did not work properly because of those same caps to black crusty pads; several scopes with the latter.

cap

[JVG]

I have never seen a TDS510A. All of the other scopes definately had them, numerous 544A's and 540A's. Has allot to do with hours used, 520x/620x type scopes are often great sources of parts or for repair simply because the go unused if a more capable 540x/640x machine is availlable. But that depends on the resources availlable on a bench. If your scope was rarely turned on to begin with... But some are ran 24/7 until they stop.

I have had 544A's that ranged from shiny new looking cap/pads that did not work properly because of those same caps to black crusty pads; several scopes with the latter.

cap

Well, my unit seems to be barely used... or in a very clean environment!. All cap pads look shinny . I will anyway later replace them, but it will be an easier job that way

I have just got the power suplpy out of the oscope. It has a couple of already replaced components (nicely done) but otherwise it is close to pristine. ZYTEC part number is 22917400 and customer part number is 620-0063-03. It is dated 9439, which seems to agree with other components on the unit.

I have seen that the 520B supply is not exactly the same but hope it has enough similarities to be useful to troubleshoot this one

I have the unit on the bench and I wonder if there is an easy way to trigger the POWER ON on it.

I will start by checking ESR with the ESR meter... perhaps I am lucky and it is such a simple thing (I am not too confident about this but, who knows!)

Regards,

JOSE

[nctnico]

To fix complex power supplies like these it often helps to use a bench power supply to feed the control circuitry (make sure to fool the undervoltage lock out). The next step is to put something like 30V on the primary side instead of mains. You can also do the same for the secondary outputs. This will allow you to verify whether all the semiconductors and post regulators work without having to deal with lethal voltages.