How to calibrate Hameg HM1500-2? - Page 1
Forum section: electronics / repair

author: youngwug
author_rank: Contributor
timestamp: February 10, 2020, 11:05:14 am
content: I have a Hameg HM1500-2.Self calibration was performed, but Ch.1 & 2 are different.Ch.1 & 2 have seven Trimmers each.1. White2. Black3. Blue4. White5. Silver(Nude)6. Orange7. Silver(Nude)What should I adjust?A manual with calibration sequence is required.It is different from HM1505 in this form.Please provide the service manual and circuit diagram if available.

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 10, 2020, 01:26:47 pm
content: Sorry no schematic our calibration procedure.If I understand your problem correctly you have a difference in gain (amplitude) between CH1 & CH2?First make sure which (if only one) is wrong. Set the offset to zero on both traces feed a DC voltage to both channels and to a calibrated voltmeter.Repeat this through all the V/Div. settings that your voltage source will allow you to, note each channel and attenuator setting that doesn't agree with your voltmeter.On the oscilloscope use the graticule (not digital readout / cursors as that could be out of calibration) to read voltages, re-check the GND position of trace regularly, better doing all checks and adjustments on a warm (30 min powered) scope.On your frontend photo there has been some leverage on the PCB near number "6" check no components are damaged.Trimmers 1,2,3,4,6 look like variable capacitors for HF compensation, you want to leave those alone if possible.That leaves 5 and 7 that could be for adjusting gain or offset.Whether it is worth touching them depends a lot on the results of your DC voltage check.It would also be good if you could find test points somewhere just after the frontend shieldings that allow to compare the voltages for each channel there as your problem could also come from the channel multiplexing just after.

author: youngwug
author_rank: Contributor
timestamp: February 10, 2020, 08:56:11 pm
content: shakalnokturn thank you very much.Gain adjustment was Trimmer # 5.The TDS2024 is used as a reference measurement.Ch.1 must be adjusted to Max to barely reach the target point. (The end of the trace is slightly swept due to the maximum adjustment.)However, Ch.2 is a stable adjustment.Ch.1 & 2 have multiple caps (10V, 100uF & 16V, 100uF).Will replacing these make Ch.1 stable?

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 10, 2020, 09:24:10 pm
content: I'm really not convinced replacing the SMD electrolytics will help here. Measuring ripple at each cap will give you some clue towards there being any point.The problem here is that although adjusting the front-end gain trimmer gets you back to a just-about acceptable state it may only be compensating for a problem further down stream or in the auto-calibration loop. That's why I suggested looking for test points directly after the front ends to compare them.Readjusted as-is what happens after a new self cal.?To me (but I could be wrong) the fact that it has a self cal. function, means that the scope must be able to inject (does it ask to remove any input from BNC's during self cal.?) a reference signal to the front-end, cycles through each attenuator setting, measures the amplitude digitally and at some point in the signal path applies the adequate gain/attenuation to keep the digital calibration happy.This means that your problem can come from numerous places depending on the scope's design: Main analog signal path, reference signal switching, variable gain stage, analog switching before self-cal. ADC...IMHO there are many things to go through before turning trimmer 5, the fact alone that having it turned right up is hardly enough to get the right amplitude is saying that the problem is elsewhere...

author: youngwug
author_rank: Contributor
timestamp: February 11, 2020, 05:44:01 am
content: New self cal does not change.I purchased the broken HM1500-2 for $ 50 in May 2018.The seller said that there was no Volts movement in Ch.1.I checked and it was the result of a failure of the front panel operation.I waited for the service manual to appear, but there was no news.Opened Ch.1 in January 2019.Visually, this circuit did not have a problem. However, we confirmed that the signal of Ch.1 is small.I waited for the service manual to appear again.There is no news on the Internet.And in February 2020, I tried to read more details, but I also need a service manual.Nevertheless, with the help of shakalnokturn, the primary cause was solved.I will also wait for the service manual to appear.I am waiting for a service manual because the knowledge I know is sometimes wrong.You also need a service manual to track signals, identify, measure, and adjust components.(In my experience, I've seen a lot of cases where some service manuals make very important things wrong. It's as if you're spraying open source code on the Internet with a few changes. They don't just give the code they developed and generated very hard.)Thanks again for shakalnokturn's help.

author: sxn1
author_rank: Newbie
timestamp: February 11, 2020, 09:37:37 am
content: I found thishttps://www.radiomuseum.org/r/hameg_oscilloscope_hm1005.htmlsorry wrong number