HM1507 - Page 1
Forum section: electronics / repair

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 25, 2018, 03:46:53 pm
content: Hello everyone! I have a failed Hameg HM1507 oscilloscope on the readout display. It works very well when I disconnect the J7002 connector from the "digital board", and when the connector is reconnected, the trace with the inscriptions move and become blotchy. I checked first the supply voltages: they are good and well filtered. The failure seems to come from the "digital board" around the integrated circuit (hybrid "readout"). I saw the chemical capacitors on the board, they are all good (the initial failure was the same). I have unsoldered some cms components around, but they are good too. I attach photos of the display failure, as well as some schemas. Thank you for you precious help!

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 25, 2018, 03:47:32 pm
content: the following......

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 25, 2018, 04:03:31 pm
content: the following.....

author: oldway
author_rank: Super Contributor
timestamp: May 25, 2018, 07:42:11 pm
content: I know that my answer will not help you but I give it to you anyway.From a certain device complexity, the proper method of repair is to have a set of replacement boards that work and that have been removed, for example, from another HM1507.Before starting desoldering anything (you can cause more problems), it is necessary to identify WITH 100% CERTAINTY what is the defective board.Only then can you make a fault search on the defective board.I recommend starting to compare the failed board with the working one with a component tester without powering it on.

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 25, 2018, 09:53:06 pm
content: I second oldway, you need another scope.So if I understand right you are seeing the problem in analog mode with readout? With readout disconnected display is stable.How are things in digital storage mode?There is sometimes a jitter adjustment for the digital readout. BTW there is a dirty/corroded spot over a sop8 and trimpot.Although you have checked capacitors, try measuring ripple at IC7040 and IC7036A.Check interconnect ground lines, beware of the red connector, I have seen them develop bad contacts at the crimping before.

author: 4thDoctorWhoFan
author_rank: Regular Contributor
timestamp: May 25, 2018, 10:51:46 pm
content: In the second picture you posted showing the circuit board, what is that spot around the pot in the center of the picture?It's hard to see from the picture, but is that corrosion, old glue or did something spill inside the scope onto the board?If it is some sort of a contaminated area, I would try and clean it before proceeding further.

author: LateLesley
author_rank: Frequent Contributor
timestamp: May 26, 2018, 01:46:48 am
content: Around the right-middle of the board, there's two tantalum caps, have you checked those? At the left of the pic, just next to the first electrolytic from the bottom, what's going on over that part of the board? it doesn't look "tidy".Also can you check the voltage reference and power supply points to the two DACs? possibly a wobbly Vref?http://www.analog.com/media/en/technical-documentation/data-sheets/DAC312.pdfEDIT: also have you noticed the two "bodged" surface mount caps just below the DACs? are they good?

author: Chris56000
author_rank: Frequent Contributor
timestamp: May 26, 2018, 09:46:02 am
content: Hi!Forgive me for stating the obvious - but have you checked the preset adjustments for Intensity/readout intensity (refer to the full service-manual) - it looks to me like it's smearing due to the intensity being far too high - most scopes of this type I've seen, Hamegs in particular, aren't designed to operate with such a high degree of readout intensity, and there may be a fault in the CRT grid bias circuits!Turn the intensity right off on both the trace and readout, then gradually increase the trace intensity until it just becomes visible - if it is still badly smeared, try disconnecting the readout board again, if you get a clear trace, the fault may be in the interface between the digital parts and the intensity-mod circuitry!Can anyone upload the complete HM1507 Service Manual or PM it to me please? I can't find it anywhere (to buy even!) and R & S only send me user manuals every time I've asked them for one!Chris Williams

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 26, 2018, 10:09:30 am
content: Hard to tell from the photo but it does look like jitter, either the digital readout not syncing to the timbase properly or an unstable Xout from the digital section.

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 26, 2018, 10:33:33 am
content: Hello; originally the failure of the oscilloscope was in the CRT (no trace on the screen); the components circled on the diagram were defective. After replacing the latter the trace is back, very thin and bright, but the inscriptions on the screen move and are mushy (when a short time is selected on the screen, it is there that the defect is visible; much less when increasing the scanning speed). I enclose the diagram to show you what I have replaced ..... Thank you for your help

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 27, 2018, 05:48:18 pm
content: Good evening; the trace should be just as blotchy and bright when removing the J7002 connector, and that's not the case. The CTR, I do not see what else could be (breakdown blanking?). In any case, the TRC card has already been verified, and I do not see anything abnormal. By cons, the 2 potentiometers, I have not deregulated. What's their point??

author: TerraHertz
author_rank: Super Contributor
timestamp: May 28, 2018, 01:06:46 pm
content: Do you have a working scope of any other kind?Looks to me like a noisy X amplifier output, with possibly the noise being injected from the digital board? Both the trace and readouts are affected.If you look at the X deflection signal with another scope, tracing it back through the system, you may find where the crap is coming from.

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 30, 2018, 08:22:53 am
content: Hello, thank you for your help, I am already lost. I have already first verified the supply voltages: they are all good, and well filtered! Where I do not see is when I disconnect the red connector J7002, and the, the trace is thin and clear. I tried in xy mode (connector J7002 remit), same failure: trace and fuzzy characters, unstable! Very strange; I do not understand anything!!! (see photos)

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 30, 2018, 08:24:32 am
content: the following

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 30, 2018, 08:25:07 am
content: the following

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 30, 2018, 12:47:26 pm
content: Here's what I got on the screen of my oscilloscope on the final stage of the horizontal amplifier, connector j7002 plugged in and unplugged. The noise is therefore the origin of the failure; in xy mode it's the same. I join a series of photos ..... Thank you for your help

author: lionelkjh
author_rank: Frequent Contributor
timestamp: May 30, 2018, 12:50:41 pm
content: the following