Tektronix 2247a menu and readout issues.  - Page 1
Forum section: electronics / repair

author: schulteaaron5
author_rank: Contributor
timestamp: August 01, 2016, 05:47:59 pm
content: Hi, the scope I just picked up won't display the divisions readout and also won't display the menu. Well not in any legible manner at least, there is a picture of the issue below. First thing I thought was to factory reset the menu, except o cant do that without seeing the menu. Maybe somebody with a similar scope can give me the exact buttons to press to factory reset. Or maybe somebody knows that I have a different issue?Sent from my A0001 using Tapatalk

author: singapol
author_rank: Frequent Contributor
timestamp: August 01, 2016, 08:01:10 pm
content: 2247A user manual only up to chapter 5. (6,7,8 not included.)Read page 2-22 , 3-6 to 3-7.http://tvory.com.ua/tektronix/tek2247a-operators-manual.pdf

author: schulteaaron5
author_rank: Contributor
timestamp: August 01, 2016, 08:13:40 pm
content: Quote from: singapol on August 01, 2016, 08:01:10 pmI tried all those options except the trace rotation. And no menu pops up with the menu controls. The service menu manual is further in that manual you listed (and notably different than regular menu controls). But even that gives no legible menu options and the factory reset is unreachable simply by pressing buttons hoping they will work.Sent from my A0001 using Tapatalk

author: David Hess
author_rank: Super Contributor
timestamp: August 02, 2016, 01:30:32 am
content: I doubt factory reset will help you but here it is:Press the top and bottom menu buttons simultaneously.Press 2nd menu button from top 3 times.Press 3rd menu button from top.Press 2nd menu button from top.Press 3rd menu button from top.Do the position controls move the traces beyond the full vertical area of the CRT?

author: schulteaaron5
author_rank: Contributor
timestamp: August 02, 2016, 03:13:21 am
content: Good call, factory reset did not work. And the traces (which I assume to be solely the waveform) do move above and below the CRT when I use the vertical position knob. I didnt attempt to adjust readout heightSent from my A0001 using Tapatalk

author: singapol
author_rank: Frequent Contributor
timestamp: August 02, 2016, 05:00:11 am
content: Try to measure using cursors the test cal signal.If the readout is still small it could mean the ic or opamp is bad.Please refer to service manual of the readout section/circuit.

author: David Hess
author_rank: Super Contributor
timestamp: August 02, 2016, 05:10:25 am
content: Quote from: schulteaaron5 on August 02, 2016, 03:13:21 amFrom what I remember, CRT calibration is all handed with trimmers so there is nothing to reset and there is no readout gain or position adjustment separate from the trace position circuits. The source for the trace position signals is different than the readout signals so that points to a problem with the vertical readout circuit.I think you are seeing a problem around U2414 shown on schematic 9. The position and readout signals join up before the vertical CRT amplifier and the vertical position and gain adjustments and your position control signals work so I do not think the problem is after U202 shown on schematic 2.There is a cable between the readout circuits on the processor board and main board which should be checked.I am sure this can be repaired.Also, this is one of my favorite oscilloscopes. The gated universal timer/counter is incredibly useful and it supports dual delta delayed sweep although I always forget how to enable it. (I looked it up; setup a standard alternate sweep and then enable time measurement.)

author: schulteaaron5
author_rank: Contributor
timestamp: August 04, 2016, 05:06:33 pm
content: Awesome! sounds like I should be able to fix this! I understand most of what you're saying, and if I can find these schematics I can get started troubleshooting....which might prove difficult for me. I'm not very experienced and this is the only scope I have, so that leaves me with a couple multimeters to get the job done. I'm going to read the "readout system" a few times to get a grip on whats going on...and I found the schematics, except "diagram 9" is missing, which seems to be the one I need...I do have a 30 day return policy on the scope, but it sounds like you think it's fixable. Although I'm still going to try to fix it in the some 20 days I have left. If I can't which is probable given how busy I am, I should keep this thing right? Twas only 50 bucks, but I'm not sure I want to spend another 50-100 and go through the trouble of finding another scope.

author: schulteaaron5
author_rank: Contributor
timestamp: August 04, 2016, 07:04:26 pm
content: Sooo scratch that, it took a OCR reader and some tedious searching but I found the schematic you must have been looking at, looks like there are a couple op amps leading out..but other than that its a pretty simple circuit, not really sure where the op amps output goes, presumably toward the CRT amplifier? Something I shouldn't touch? don't reaally wanna die for the scope. I guess I'll be probing the web on how to test this with my multimeter without dying, any help here will be much appreciated too! Here is a photo of the local circuit so its available, (I'm looking at u2414)

author: David Hess
author_rank: Super Contributor
timestamp: August 04, 2016, 11:17:39 pm
content: That is the schematic. It took me a second look to figure out what how it works.There is a full scan of the service manual here:http://w140.com/tekwiki/wiki/2247AProbing with a multimeter or oscilloscope is pretty safe in this area. Just do not allow your probe to slip and short out adjacent pins. It helps to have a sharp probe tip. The chassis frame can be used as ground if necessarily.As I said before, physically check the cable which goes between the readout circuits on the processor board and main board.For the circuit itself, we are looking at a massive offset and gain error which is probably just a gain error dividing the output in half. I tried on my 2247A and unfortunately I do not think there is any way to get a clean controllable test signal. There might be something in the service manual theory or repairs section about it though; I have not checked.I think the most likely failure is U2414 followed by U2416. It may be safest to just replace them. Install sockets if you do this. U2412 could be bad but will be more expensive so I would replace the other first if you go this route.

author: schulteaaron5
author_rank: Contributor
timestamp: August 05, 2016, 07:38:28 pm
content: Where would I find these chips anyway? Nothing on eBay or google...do I have to buy another broken scope?Sent from my A0001 using Tapatalk

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2016, 12:00:48 am
content: Quote from: schulteaaron5 on August 05, 2016, 07:38:28 pmThese are all standard ICs which are still in production and available inexpensively. If you replace any of them, then I suggest installing a socket or collet pins. The board is all through hole, right? I have not had my 2247A apart in a long time.U2416 - TL074 Operational AmplifierU2414 - 4052 CMOS Analog MultiplexorU2412 - DAC08 8-bit Multiplying DACU2411 - 74HCT374Also before replacing any ICs, check the value of R2413 and R2414 which are connected to U2412 and check the value of R2410 which are close to the output and connected to U2416.

author: schulteaaron5
author_rank: Contributor
timestamp: August 06, 2016, 12:09:17 am
content: How did you know that though? I wish...And why am I checking these resistor values? Something to do with chip voltage compatibility?Sent from my A0001 using Tapatalk

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2016, 06:08:32 am
content: Quote from: schulteaaron5 on August 06, 2016, 12:09:17 amThe part numbers are right on the schematic in this case.QuoteThese resistors all control the gain from the DAC input to the voltage output of the circuit.

author: schulteaaron5
author_rank: Contributor
timestamp: September 07, 2016, 07:10:41 pm
content: So life is busy and I'm just getting to replacing these chips. I'm sure I have at least one compatible chip. I have a cd4053be and a 74hc4052n. I'm gonna go with the 4052 like you said. I bring up the 4053 because it confuses me that ti only has a datasheet for 405x chips, as if there is little difference. Also is there a difference between 74hc and CD prefixes...why is it even like this? Just different manufactures? Thanks again for all your help! Really appreciated!Sent from my A0001 using Tapatalk

author: singapol
author_rank: Frequent Contributor
timestamp: September 08, 2016, 01:45:33 am
content: Quote from: schulteaaron5 on September 07, 2016, 07:10:41 pmIt's always wise to use original type or compatibles...why? it has to do with device power supply. For examplecmos 4K series can be powered up to 18V vs 74HCXXXX types at only 5V for low power but equivalent speedas old 4K series. You would probably kill the 74HCxxxx and damage some other circuits so use 4K cmos version. PS HC stands for high speed cmos. Also do note there is a difference between HC and HCT types...a difference between what constitutes a low or high digital voltage level for cmos and TTL logic.

author: schulteaaron5
author_rank: Contributor
timestamp: September 08, 2016, 02:27:36 pm
content: Quote from: singapol on September 08, 2016, 01:45:33 amThanks a lot for the info. I checked over the datasheets for both and the 74hc4052 does have lower voltage thresholds than the cd4053. You said that 4k series CMOS should have that +/- 20v power inputs. But isn't the 74hc4052 a 4k series CMOS as it is not the TTL version labeled HCT? Also what does CD then stand for? Thanks again for the helpSent from my A0001 using Tapatalk

author: David Hess
author_rank: Super Contributor
timestamp: September 08, 2016, 03:55:37 pm
content: Quote from: schulteaaron5 on September 08, 2016, 02:27:36 pmIt is not the CD part which is important although I think it means CMOS Device. The important parts are 4052 versus 74HC4052. The former is a 4000 series CMOS part and the later is an 74HC series HCMOS part.

author: singapol
author_rank: Frequent Contributor
timestamp: September 08, 2016, 04:32:38 pm
content: Quote from: schulteaaron5 on September 08, 2016, 02:27:36 pmDifferent companies/brands use different alphabet prefix to distinguish their products. CD is the prefix used by Harris semiconductor which I believe no longer exists as it has merged or aquired by a larger company.If you are interfacing pure cmos circuits then you would use 74HCxxxx but if your cmos circuit is also interfacing with older TTL logic then you would use 74HCTxxxx. The T stands for cmos to TTL . Reason being the cmos logic levels are translated/level shifted to and recognised by TTL logic as a logic 1 or 0.HC/HCT family are low powered high speed logic powered by 5V only where as cmos older 4K logic family can be powered usually by 15V VCC. So if your old circuit is 15V you can't substitute a 74HC/HCT device.