hung chang 5510 oscilliscope repair - Page 1
Forum section: electronics / repair

author: The_Todd
author_rank: Regular Contributor
timestamp: September 07, 2017, 06:16:58 am
content: hello Guys,I scored an old Hung Chang oscilloscope that is not working and wondering if it can be fixed.When you turn it on there is no trace and all there is is a large out of focus dot hard left.no amount of adjusting fixes it.this also looks like its been attempted to repair before, there is new markings on the various sockets where the baords been taken out and solder points have been re soldered.All input voltages are correct.pretty much all the caps are done, either low capacitence, high (some very high) ESR and some up to 40% voltage loss.a lot of very suspicious solder joints. some traces are even cut. im not sure if this was from factory or someone troubleshooting :SSo what are the chances of repair, and I cant find the correct service manual anywhere :Scheers,

author: Zucca
author_rank: Unknown
timestamp: September 07, 2017, 07:07:52 am
content: it will be a long journey. Good luck.

author: Armadillo
author_rank: Super Contributor
timestamp: September 07, 2017, 07:19:36 am
content: A simple push-pull horizontal amplifier to CRT coil around block Q801 to Q812? if I can remember correctly. Just probe for the sawtooth waveform and DC supply voltage [140V?]Hope it helps.

author: tautech
author_rank: Super Contributor
timestamp: September 07, 2017, 07:48:09 am
content: On a bit of chase to find Hung Chang manuals I found this dubious link:https://wiggstanwebpha.jimdo.com/2017/04/13/hung-chang-oscilloscope-manuals/Clicking on it gives a 620 Kb zipped file that when unzipped offers a link to an 84 Mb Manuals file from cpgweb.net.Options to Run, Save or Cancel.Looks suspect but if your antivirus is all up to date it could be worth looking at.Here's another for the 5504 of which it seems the 5510 is of the same series.jaboxajimosej.tk/9143744/894c9d47-hung-chang-5504-manual-412aecc06You'll need the service manual to proceed far with this unless you've had considerable CRO repair experience but as you have something on the display you're a long way towards getting it sorted.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 07, 2017, 07:56:03 am
content: well, that's interesting Q801 a utc4558 has pin 3 un-soldered by the looks of it, by the last person who fiddled with it. when I connect it, the dot disappears, disconnect it and the dot comes back and even does a single right sweep then dissapears.This rabbit hole looks deep.

author: Armadillo
author_rank: Super Contributor
timestamp: September 07, 2017, 08:03:15 am
content: Quote from: The_Todd on September 07, 2017, 07:56:03 amThe front trigger knob, set to click and put to auto first, otherwise it may not trigger.Also base of Q801, probe is there sawtooth entering base?.Either the sawtooth Gen or the horizontal amplifier or simple still, the trigger knob not properly set to auto.Please use probing and measuring, don't use rabbit hole.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 07, 2017, 09:11:42 am
content: ok, no saw tooth, just static, according to my cheap DIY scope. chips is getting 23v and it it amplifying..something....thats by check bot the input +/- of both sides of the chip

author: The_Todd
author_rank: Regular Contributor
timestamp: September 07, 2017, 09:21:58 am
content: Also the trigger light is going off now and then if thats any good info for you haha

author: Armadillo
author_rank: Super Contributor
timestamp: September 07, 2017, 10:20:45 am
content: It would be good to get the basics done up first;Clean all the mechanical contacts with contact cleaner.Set Sweep mode to AutoSet Source to CH1;All knobs to detent positions.All pull knobs to down position.Sweep to 5us/div, shake abit.Try horizontal sweep mode 'A' and then 'B'. [there are 2 sweeps gen]Most of the time, the contacts are dirty.After that check that sweep A and Sweep B are pulses available.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 07, 2017, 10:41:16 am
content: Quote from: Armadillo on September 07, 2017, 10:20:45 amOk next day off ill give it a serious clean out,It looks like its hard a hard life, but a dual 100mhz may still be worth the effort

author: The_Todd
author_rank: Regular Contributor
timestamp: September 07, 2017, 01:04:39 pm
content: Ok so an update, Ive been reading lots of forum posts and guides and found somthing interesting.If i turn the lights off, put intensity up high you can see a glow, and there is fact a sweep left to right and it chnged speed with division change. I think its sitting above the visual screen. And when you turn off, then on again there is a single sweep in the middle of the screen.At least I know shes alive

author: Armadillo
author_rank: Super Contributor
timestamp: September 07, 2017, 01:16:34 pm
content: Quote from: The_Todd on September 07, 2017, 01:04:39 pmSo the picture with the stationary bright spot in the middle is not longer valid? In that case we should be looking at the vertical. Its the vertical knob able to adjust the trace down. Can you ground the channel input and adjust the vertical knob to move down the trace?

author: The_Todd
author_rank: Regular Contributor
timestamp: September 07, 2017, 01:45:34 pm
content: Yes, I for got to mention I resoldered Q801 properly onto the board wich sloved the sweep problem.I tested in sweep mode and x-y mode and no change at all to vertial even when grounded or knobs adjusted on both channels. It is literly stuck.

author: Armadillo
author_rank: Super Contributor
timestamp: September 07, 2017, 01:54:04 pm
content: Quote from: The_Todd on September 07, 2017, 01:45:34 pmI don't understand if you can test the sweep in x-y mode.?I thought you will need input into both the X and Y to operate in that mode?

author: The_Todd
author_rank: Regular Contributor
timestamp: September 07, 2017, 02:14:11 pm
content: So, in normal mode I can see the sweep (wich is just a glow moving across) , but i put it in X-y so the "dot" stayed still, wich would make it easy to notice any sudden movement. But in any mode, there was no vertical movement using grounding, test signal or vertical adjustment.

author: Armadillo
author_rank: Super Contributor
timestamp: September 07, 2017, 02:26:53 pm
content: So vertical should be much simpler than the horizontal right?apply the calibration square wave into the channel input and trace the signal along the vertical amplifiers should be the way to go.check IC 2? for the signal output .Edit: It's better to visual that the CRT vertical coil is not messed up by the original user, also check the connectors..

author: The_Todd
author_rank: Regular Contributor
timestamp: September 08, 2017, 11:04:34 pm
content: Hey still haven't had a chance to re test.i REALLY wish i could find a 55xx series manual, as these are quite different layout to other models, and also to check all these pots in case they were adjusted :S and tracking back the amp signals is a bit of a jungle.how do i check the CRT coil? also if i disconnect the Y wires, will this theoretically bring the sweet to the center (if it is safe)cheers,

author: Armadillo
author_rank: Super Contributor
timestamp: September 09, 2017, 02:47:31 am
content: Quote from: The_Todd on September 08, 2017, 11:04:34 pmSafety first.The scope does carry High voltage and proper discharge and safety technique must be used. If you have not done it before, and not comfortable in dealing with it, then I suggest you ask a friend to help you out with the repair.I don't have the manual, maybe others have it. I search the internet but non is available also. Many sites are virus and fake.Otherwise a bit of tracing is necessary.Vertical off the screen, can use the "common moding" technique [easier if you have the schematic].If you have a oscilloscope to trace the signal, it would be much easier to troubleshoot the scope."Visually" as long as the CRT is not meddled with, you should be checking the preamplifier and the vertical amplifier first. Clean the contacts and meddle with the front panel buttons would help, channel 1 or Channel 2, chop or invert etc...Without the Y, the trace should revert to somewhere center, but it would be easier if it has the "Find trace" button like the Tektronix scope.

author: tautech
author_rank: Super Contributor
timestamp: September 09, 2017, 04:09:25 am
content: Another look finds these are also sold as Protek so identifying the model # Protek might help you find the manual.

author: oldway
author_rank: Super Contributor
timestamp: September 09, 2017, 08:51:11 am
content: Without service manual or, at the very least, schematics, it seems difficult to repair this oscilloscope.It seems that there are multiple failures and even problems resulting from attempts at repair.Moreover, it is not a very common model.If it were Hung Chang OS-620, that would be easy, I have already repaired several.*But this model, I've never seen it.One positive point is that there is high voltage.For the rest, it will be necessary to follow the usual principles:1) check the supply voltages2) repair bad contacts and bad solder3) repair the damage of previous repair attempts4) with the type of crt, check the pinout and measure the voltages of the vertical and horizontal deflection plates (Caution: there is high voltage on some pins of the crt)5) Check horizontal and vertical amps in X / Y mode and repair them.6) check and repair the focus and brightness circuits ... (high voltage probe recommended)7) check and repair the trigger and time base ..But it is not possible to help you to do this from a forum....You will have to do a lot of reverse engineering.

author: Armadillo
author_rank: Super Contributor
timestamp: September 09, 2017, 09:47:08 am
content: See the Hung Chang generic block diagram of the vertical, should helps you in tracing the circuit.Also attached the schematic of the Hung Chang scope, though it is not specifically 5510, but should give you a better guide to start tracing..Hope it helps;Edit: See page 1 of the schematic, you can see signal routing through those selector switches, now isn't it a good place to start probe for the signal?

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 06:30:04 am
content: Quote from: Armadillo on September 09, 2017, 09:47:08 amHey this is really good thanks,So here is some info for youAll voltages are in XY mode and earthed to chassis.X - 57v and 84vY - red- 104v. White 6.8vI have also taken a scope reading from the delay line going to the amp circuit. These were taken with the test signal on line 1. 1st pic was taken with position on max and second on minimum. Does this look out of the ordinary? This should help isolate witch side of the circuit is at fault. Both wires give same kind of reading but slightly different voltage levels. And also when the delay cord is removed sweep is dead center on screen .CheersSent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 06:35:35 am
content: And to add more data on stationary.XY mode with no input. The voltages on delay line areWhite -0.947vRed +0.536v (however red was not stable and kept creeping up)Sent from my iPhone using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 06:55:40 am
content: Quote from: The_Todd on September 10, 2017, 06:35:35 amWell done good progress. You can adjust the center position and Gain later. If the 2 oscilloscope traces are from the delay lines and it can center the spot onto centre, means its looking very good. No rabbit hole. You are getting close.You should be looking at page 3 of the schematic. Looks like the vertical amplifier is the problem then.Edit: According to 60Mhz Hung Chang Scope, the 2 complementary output from the delay lines should be only 12mv [Peak to Peak], both same. Is your scope accurate? Well, you can adjust the gain and center position later, so repair the vertical amplifier first.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 07:13:40 am
content: Quote from: Armadillo on September 10, 2017, 06:55:40 amHaha probably not, it is cheap. However if the signal is lets say 1v over total, wont i make all signals to high anyway? Also I tested the final CRT out put there is a small change in the square wave signal when i adjust vertical, but obviously not enough to center on screen.In regards to the amp circuit, this is reaching the limits of my circuit analysis , but does the circuit supply the +/- independently or does it actually balance the 140v(?) between both poles?Sent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 07:21:03 am
content: Oh and here is a physical pic of the amp circuit in questionSent from my iPhone using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 07:26:02 am
content: Quote from: The_Todd on September 10, 2017, 07:13:40 amOn your test scope, use AC coupling, no need to use DC coupling. Set the probe to 2.5V/Div as indicated there on the schematic. The objective is to find which side is defective of the Y+ and the Y-. So you should be probing both, the Y+ to ground and the Y- to ground to determine which side of the complementary amplifier is not firing. After finding the defective side, you can begin to probe through those transistors to identify the problem.Its like a complementary push and pull amplifier.

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 07:28:56 am
content: I think you need to bring it out of the house and use compressed air to blast it.Man, its so dusty.The space is tight, so careful there.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 07:34:11 am
content: Sorry, just saw the probe picture.The negative (i think) white wire before the inductor/resistor mesures at 6.88v with no input in xy modeAnd just to report red in same point mesures at 108.8vAlso in case I didnt already say, thanks for the help, the osciliscope is much easier to understand when broken down to secitions.Cheers.

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 07:41:45 am
content: Quote from: The_Todd on September 10, 2017, 07:34:11 amOh I see, seems like you need to check for open resistors or verify the ohms [with the power OFF], why only 6.88v?You are welcome, No rabbit hole.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 07:43:57 am
content: Ok lets try this again.So here are the pics of Y +/- both exactly same settings and at the point before inductor/resistor. This is with the internal test signal. The one with the red pen is the red wire (Y+ i assume)CheersSent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 07:56:30 am
content: Also, its been bugging me, seing as the last person had ic801 unsoldered, is there a chance they "fiddled" with the pots on the amp curcuit and this could be causing more "push" the "pull"?

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 08:01:14 am
content: Thanks, the DC bias voltage don't seem right. Can you verify with volt measurements shown in schematic.At least both the Y+ and the Y- side must be the about same DC bias voltage to pull trace down to center.Was you saying the Y+ at 108V and the Y- at 6.8V? [don't use color white and Red, can't see it here]Check for open circuit, resistors, 2 two capacitors etc...[Caution reminder. Ohm measurement only when POWER IS OFF].I think the last guy attempts everything including misadjust the pots for you.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 08:09:55 am
content: Quote from: Armadillo on September 10, 2017, 08:01:14 amSo where you have 37v circled is where i tested. there is no input and it should be center. This is why the sweep is hard top of the screen.I was reading some info about pull push circuits. Should both signals have the same 0v level? (In this case after delay cable)Also pic of the infamous red/white wireSent from my iPhone using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 08:23:42 am
content: Quote from: The_Todd on September 10, 2017, 08:09:55 amSo the Y+ and Y- DC bias are the same? [I circled the Y- side, how about the other Y+ side]Y- Side = ? volts;Y+ Side = ? volts;If both side not the same, then you should be tracing and finding the cause of the not the same.Basically both sides like a mirror. So their value should be the same. So finding the faults should not be too difficult? right?

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 08:27:27 am
content: Ok so we are clear, with NO input (flat line) Y+/- should be the same?Also in this situation what should both the signals looks like after the delay line? Also same volatages?Cheers.

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 08:35:58 am
content: Quote from: The_Todd on September 10, 2017, 08:27:27 amAfter delay lines, both the same pulse voltage - YES. But don't need to bother now, if the DC bias at the amplifier is not the same. There is also the front panel vertical offset potentiometer that can alter the two sides, set it to centre.Can you pull out these components and measure/verify it.? [From both sides] apple compare to apple.Can you fill in the voltage so that I can visualise the unbalance.Y- Side = ? volts;Y+ Side = ? volts;Edit: Do contact clean the potentiometer especially the vertical offset. I would check it in this unbalance case.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 08:42:08 am
content: Woah, very tricky atm with everything as it is.For the moment can i masure in curcuit and compare to mirror componet?

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 08:45:20 am
content: Quote from: The_Todd on September 10, 2017, 08:42:08 amCan you fill in the voltage so that I can visualise the unbalance.Y- Side = ? volts;Y+ Side = ? volts;Yes you can measure in circuit, but when one side measure 108v and the other 6.6v then no choice situation.Take your time and enjoy the repair. No hurry.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 08:47:36 am
content: Ok, as in voltage directly going to CRT?

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 08:50:13 am
content: Quote from: The_Todd on September 10, 2017, 08:47:36 amhere and here

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 08:55:44 am
content: Ok, with no input, xy mode and vertical adjustment put into middle.Y+ (red) 104.8 vY- (white) 6.87vAnd just for fun, with delay cable removed...Y+ 32.14Y- 32.27Cheers

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 08:59:55 am
content: Quote from: The_Todd on September 10, 2017, 08:55:44 amThanks, you got a point there. You are right.Can we revert to troubleshoot before the delay line.Please measure the voltage at the delay line; [Before the delay line]Pin 1 to Pin 2 DC voltage = ? volts;Pin 3 to Pin 2 DC voltage - ? volts;

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 09:07:36 am
content: Can you check attached also;maybe the adjustment way out or the potentiometer is defective?

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 09:11:50 am
content: Quote from: Armadillo on September 10, 2017, 09:07:36 amOk ill check it out.I also checked out the delay cable with AC mode this time, red pen for red wireSent from my iPhone using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 09:13:50 am
content: Please measure the voltage at the delay line; [Before the delay line]Pin 1 to Pin 2 DC voltage = ? volts;Pin 3 to Pin 2 DC voltage - ? volts;Also attached;

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 09:20:01 am
content: Sure thing. As usual done with no signal (flat line)EDIT: this time with corect mode on multimeter.Pin 1 (red) +0.853vPin 3 (white) +1.624v

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 09:25:29 am
content: Quote from: The_Todd on September 10, 2017, 09:20:01 amHow can the +8V supply there doing nothing.?Can you re-measure again and check all the DC power supply voltages. From your trace, the red probe is lobe sided not centre despite AC coupling, so check all the DC power supply voltages.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 09:28:09 am
content: Sorry I completly read that wrong, can you send me the full diagram to review.I thought you meant pin 1-2-3 on the delaywire.

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 09:29:03 am
content: Quote from: The_Todd on September 10, 2017, 09:20:01 amSee the Red side is lobed. Do check all the DC power supply voltages and trace faults why Red is 1/2 of white?

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 09:31:09 am
content: Could i have a bigger version of this, the pots on my board are labled different.Cheers

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 09:35:44 am
content: Quote from: The_Todd on September 10, 2017, 09:31:09 amYou mean the schematic?size limit in this forum, so you can download here;https://elektrotanya.com/hung-chang_protek_6502_04_06_20_40_60mhz_oscilloscope.zip/download.htmlWait for the display to say download.

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 09:46:29 am
content: Since lobed onto the positive side, so I think you should check the negative power supply.no hurry, take your time and enjoy the fun [the puzzle someone set for you..... hahahaaha]cheers;

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 10:16:42 am
content: Ok this will take a while to digest. But so far I know a few things. 1. The CRT monitor seems to be fine 2. The problem apesrs to be the vertical signal circuit. This will narrow things down.Now I notived on the schematics Ive got it uses 8v +/- as a reference voltage for the pots. Mine I think are using 12v any way of know knowing roughly what it is meant to be? And do all pots use the same referance voltages?

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 10:22:44 am
content: Quote from: The_Todd on September 10, 2017, 10:16:42 amShould be OK as long as +12V and -12V, AND resulting in the DC bias to the complementary output is balanced [no lobe sided].Digest the circuit and uncover why loped and check slowly while you enjoy it.Cheers;

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 12:57:52 pm
content: SHES ALIVE!!and the fix was kinda embarrassing.So after studying the Y signal circuit, I went and checked the voltages everything was ok, the pots were pretty much ok, and then spotted something weird, with the voltages right on the plug for delay curcuit.So hell, why not give it a hard push down, and eureaka, so a bloody cold solder joint. Anyway, as you can see she works but there looks like a few more problems to tackle.... but we shall call it a night and repeat tommorrow.Cheers!

author: The_Todd
author_rank: Regular Contributor
timestamp: September 10, 2017, 01:10:21 pm
content: Quote from: Armadillo on September 10, 2017, 01:07:34 pmYour mentioning that the voltages should be roughly equal, got me thinking, when i checked the circuit everything was a mirror so I justPinned down the voltage that was differentSent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: September 11, 2017, 12:49:45 am
content: So now we have a heartbeat time to fix the brain and kidneys, this is very exiting having a working scopeas you can see in the pic it produces a fairly good wave, but I wont be able to calibrate anything more until I get the correct probes (only have 20mhz ones and replace the main capacitors.Now if you see the second pic you can see how the other person tried to re-soldier the board it looks like he used a heavy rosin flux? Will this be an issue, as its all over the board :/Cheers,Sent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: September 11, 2017, 01:14:56 am
content: Oh also anyone know what these sold for bacl in he day? Just curious.Sent from my iPhone using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: September 11, 2017, 01:38:53 am
content: Quote from: The_Todd on September 11, 2017, 01:14:56 amI guess back in those days, oscilloscope should be expensive,, maybe... say... close to US$1000.00;if you are worried of the rosin flux, then clean it with IPA.Cheers!

author: The_Todd
author_rank: Regular Contributor
timestamp: September 11, 2017, 01:41:04 am
content: Quote from: Armadillo on September 11, 2017, 01:38:53 amWell now i feel special, im more worried about the extra rosin damaging the tracks over time, I may have to completly de solder and resolder to be sure :/Sent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: September 11, 2017, 02:21:11 am
content: Ah bugger just realised this is actually missing a transformer cover near the HV cucuit. Will this cause any issues?Sent from my iPhone using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: September 11, 2017, 09:24:08 am
content: Quote from: The_Todd on September 11, 2017, 02:21:11 am2 frame of thoughts, for one is the protection from physical contact, example the safety aspect and for the other is the noise/spike screening "BUT" if so then the other side of the PCB should also be screened isn't it. So I reckon more on the former thought, but not sure really. Wonder if you build a cover yourself, will it drop out and cause a short circuit? LOL!Maybe you can call the former guy and ask it from him.

author: The_Todd
author_rank: Regular Contributor
timestamp: September 11, 2017, 09:26:12 am
content: Quote from: Armadillo on September 11, 2017, 09:24:08 amHaha if I knew who the former guy was My job would not be this hard. I was thinking more or magnetic interference ect. But yeah cant be that hard to make one...Sent from my iPhone using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: September 11, 2017, 08:38:27 pm
content: Quote from: The_Todd on September 11, 2017, 02:21:11 amThe cover there is primarily for protection while making adjustments but in saying this some scopes don't have covers on the EHT or PDA. The EHT is created with a simple SMPS running ~30-50 KHz and the PDA is essentially HV DC.I'd move ahead and use the scope with the knowledge there might be some EMI or maybe not. Suck it and see.