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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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4th Jun 2019, 5:50 pm | #61 |
Octode
Join Date: Jul 2017
Location: Newcastle Upon Tyne, Tyne & Wear, UK.
Posts: 1,177
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Re: Hameg HM307-3 Cleaning and Repair
Thanks for the explanation, wme_bill. I'll have to get my head around that!
I don't have a source of the HV transistor you mentioned. I do have another BD157 or two just in case the others have went bad. I won't install them yet. I have been going through the measurements you recommended. R306 is connected correctly. Junction of R316/R318/R309: +1.4V Junction of R318/R309: -1.8V IC voltages: Input V of pin 2: 0V Input V of pin 3: 0V Output V of pin 6: -3.5V. Varies with HV adjustment. The fact that the input voltage on pin 2 and 3 is 0V is concerning. R306 removed: Input V of pin 2: 0V Input V of pin 3: -1.9V Output V of pin 6: -5.2V. Varies with HV adjustment. I won't rebuild the PSU. It could make things worse. Making voltage measurements with the scope on is the way to go but because of the high watt resistors getting hot I have been keeping the scope turned on a little as possible. When checking components out of circuit I have been making sure that they are installed the right way around and soldered properly. |
4th Jun 2019, 9:03 pm | #62 | |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,505
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Re: Hameg HM307-3 Cleaning and Repair
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WME_Bill is right. The 200v rating of the BD157 is evidently not sufficient to survive the possible transient voltages in the circuit and so failed under stress. The +163v noted on the circuit at the collector of T301 is the nominal running voltage, but the simulator confirms a much higher transient does occur for a fraction of a second at power up. The MJE13003 sounds like a good option. BTW, RS sell a KSE13003 which appears to have similar characteristics. Last edited by WaveyDipole; 4th Jun 2019 at 9:33 pm. |
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4th Jun 2019, 9:23 pm | #63 | ||
Octode
Join Date: Oct 2007
Location: Exeter, Devon, UK.
Posts: 1,553
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Re: Hameg HM307-3 Cleaning and Repair
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Removing R306 will have very odd effects, as the EHT rail will go more negative, which is why p3 goes more negative than in your first quoted reading. While as the transistor base now floats, the collector will go off anywhere and as it is suspect anyway, we just cannot guess. I suggest put R306 back, but try connecting base quickly to chassis and see what happens to the pin3 input and p6 output. Have you replaced the OpAmp. I rather suspect that should be tried. What views from WaveyDipole? Are we narrowing the fault condition down. It seems we have an original fault and some consequential failures. Just seen WD's posting #62. We both seem to agree. I always feel happier when a greater expert agrees with me. wme_bill |
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4th Jun 2019, 10:53 pm | #64 | |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,505
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Re: Hameg HM307-3 Cleaning and Repair
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One possible source for a genuine MJE13003 is this eBay seller who is generally considered to be trustworthy: https://www.ebay.co.uk/itm/MJE13003-...r/382825942544 However one can get 5xKSE13003 cheaper from RS! |
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5th Jun 2019, 12:16 am | #65 |
Octode
Join Date: Jul 2017
Location: Newcastle Upon Tyne, Tyne & Wear, UK.
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Re: Hameg HM307-3 Cleaning and Repair
I agree that the next step should be to replace the BD157 and the 741c op amp. Maybe a new socket.
Just been looking at the transistors offered by ESR. They stock BD232 transistors with a Collector-Base Voltage of 500V and a Collector-Emitter Voltage of 300V. Or a BF259? Are any of these worth trying? |
5th Jun 2019, 10:04 am | #66 |
Heptode
Join Date: Jul 2014
Location: Boston, Lincolnshire, UK.
Posts: 993
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Re: Hameg HM307-3 Cleaning and Repair
If it helps at all, 'Vintage Parts' look like a cheaper option for BF459 - I've never had a problem with anything from there, but otherwise I have no connection.
http://markhindes.easywebstore.co.uk/BF459_A1KIG6.aspx |
5th Jun 2019, 5:38 pm | #67 |
Octode
Join Date: Jul 2017
Location: Newcastle Upon Tyne, Tyne & Wear, UK.
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Re: Hameg HM307-3 Cleaning and Repair
Thanks for that Goldie99; I've never heard of them before. I have bookmarked them.
I've got some op amps and a few transistors to try. If they don't work I'll patiently wait for the MJE13003 that Wavey Dipole has kindly sent out. |
5th Jun 2019, 8:06 pm | #68 |
Octode
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Location: Newcastle Upon Tyne, Tyne & Wear, UK.
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Re: Hameg HM307-3 Cleaning and Repair
I've installed the new 741 op amp, socket and tried both new transistors. The -1000V rail is still too low!
With BD232: -1000V rail: ranges from -960V --760V. C of T301: 400V Input V of pin 2: 0V Input V of pin 3: 0V Output V of pin 6: -5.3V. With BF259: -1000V rail: ranges from -960V --760V. C of T301: 310V Input V of pin 2: 0V Input V of pin 3: 0.65V Output V of pin 6: -5.3V. What should the voltage be at the inputs of the IC? Does anybody wonder if something connected to the -1000V rail is pulling it down? I'm going to lift one end of R305 and see what I measure. Last edited by OldTechFan96; 5th Jun 2019 at 8:07 pm. Reason: More info |
5th Jun 2019, 9:03 pm | #69 | |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
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Re: Hameg HM307-3 Cleaning and Repair
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What voltages do you measure across the following individual resistors: R310, R312 and R313? |
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5th Jun 2019, 9:42 pm | #70 |
Octode
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Location: Newcastle Upon Tyne, Tyne & Wear, UK.
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Re: Hameg HM307-3 Cleaning and Repair
The measurements in post 68 were taken with the the CRT circuit connected to the -1000V rail.
Voltage across: R310: 0.241V R312: 422V R313: 422V |
6th Jun 2019, 8:02 am | #71 |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
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Re: Hameg HM307-3 Cleaning and Repair
The voltage across R310 should read slightly more than half of what you read across one of the 1.5MΩ resistors. I would say from that reading that capacitor C311 is shorted.
Last edited by WaveyDipole; 6th Jun 2019 at 8:25 am. |
6th Jun 2019, 8:58 am | #72 |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,505
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Re: Hameg HM307-3 Cleaning and Repair
BTW, I have just tried that scenario on the simulator model to see what conditions it would generate. It showed an output of -790v and the collector voltage at T301 oscillated between +200 and +400v. Furthermore, there was a negative voltage at the non-inverted input of the 741 op amp, although not quite as low as that reported. However, the conditions do seem to approximately correspond to that reported.
If this is indeed the problem, then the output returns to -1kV once the capacitor is disconnected from the circuit which should suffice for test purposes. In the long term it would naturally need to be replaced. |
6th Jun 2019, 10:26 am | #73 |
Octode
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Location: Newcastle Upon Tyne, Tyne & Wear, UK.
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Re: Hameg HM307-3 Cleaning and Repair
I have removed C311 and it tests fine. It is not shorted. With it removed the -1000V rail still reads low.
I have also checked C312 and C13 and they are both fine. |
6th Jun 2019, 11:55 am | #74 |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
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Re: Hameg HM307-3 Cleaning and Repair
Then there must be another explanation for that very low voltage reading across R310/C311. Assuming that your probes made good contact, then such a low voltage would indicate to all intents and purposes a short or at least a very low resistance under running conditions. Back in post #40 wme_bill mentioned that resistors can sometimes change value under high voltage stress conditions. Maybe R310 is OK when examined using a low test voltage, but breaking down under running conditions where much higher voltages are present. I would suggest replacing that resistor.
Last edited by WaveyDipole; 6th Jun 2019 at 12:01 pm. |
6th Jun 2019, 12:41 pm | #75 |
Octode
Join Date: Jul 2017
Location: Newcastle Upon Tyne, Tyne & Wear, UK.
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Re: Hameg HM307-3 Cleaning and Repair
I replaced R310 last week because it had drifted a bit high. I have replaced it again and we are back in business! The -1000V rail is now what it should be. You were both correct about the HV breakdown.
This shows that the new BF232 and op amp are working correctly. If I remember correctly, the last thing I did before the PSU fault was replace a zener in the CRT section. We were also investigating the lack of brightness of the CRT. |
6th Jun 2019, 3:37 pm | #76 | |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
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Re: Hameg HM307-3 Cleaning and Repair
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Yes, how is that looking now? Last edited by WaveyDipole; 6th Jun 2019 at 3:56 pm. |
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6th Jun 2019, 5:26 pm | #77 |
Octode
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Re: Hameg HM307-3 Cleaning and Repair
The resistors are from a Vellemen resistor pack. The working voltage given is 250V. 188V was measured across R310. I agree that this is a bit close.
Z352 had -900V on each side. Checked C352 (1uf 25V tantalum) and its resistance varied between 10KΩ and 20KΩ. Replaced it with a ceramic capacitor and the voltage on the cathode of Z352 was closer to what it should be. The voltages on T354 were higher than expected. Measured 140V rail and it was a bit high at 148V. The output of the rectifier was also high at 198V. I noticed that C305 was leaking electrolytic on the PCB. It was removed and the board cleaned up with IPA. R304 is good at 1200Ω. This is one of the hot resistors mentioned earlier in the thread. I replaced it with a 47uf 450V radial capacitor I had around. I probably will replace it in the future with a 250V axial capacitor. This only brought the 140V rail back to 146V, still a bit too high. I noticed in my notes that in the past the rail measured 133V. I wonder is something attached to the 140V rail is drawing less current? 140V goes to the astigmatism control and the Y final amp. Attached are some diagrams with some more voltage measurements. |
7th Jun 2019, 12:05 pm | #78 | ||
Nonode
Join Date: Mar 2013
Location: Leicester, UK
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Re: Hameg HM307-3 Cleaning and Repair
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With regards to R304 getting hot, the fault in the Y-preamp may have been a contributing factor, stressing the final stage and putting excessive demand on the supply. That might have been sufficient to make R304 run a bit hot and drag the voltage down. However, faulty smoothing capacitors can also cause such problems. With repairs having been made to the Y-amp and preamp, it one might expect it to run a bit cooler now. Of course, with a 4W resistor some heat under running conditions is only to be expected, but if it is still running excessively hot, you might also want to make sure that C307 is not electrically leaky. With regards to the voltage reading at the emitter of T354, this will vary somewhat with the input voltage, but will also very much depend on the position of the 100k preset R369. The diagram shows circa +85v, which is approximately what might be expected when correctly adjusted, but 100k provides quite a wide range of input to the base of T354 so the voltage at the emitter (i.e. to pin 8 of the CRT) will also vary considerably as the preset is adjusted. I imagine that the preset is positioned close to one end of its possible travel? May also be worth checking that R370 is not gone high. For now it might be sufficient to simply adjust the preset to obtain approximately +85 volts at the emitter, or just leave it as it is. Once you have a running trace and can display a square wave, you will then be able to adjust this control visually for an evenly spaced trace. It does sound like you are making good progress. Has the brightness of the trace improved now that you have replaced that tantalum capacitor and now that the voltage across Z352 is closer to what it should be? Last edited by WaveyDipole; 7th Jun 2019 at 12:12 pm. |
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7th Jun 2019, 5:16 pm | #79 |
Octode
Join Date: Jul 2017
Location: Newcastle Upon Tyne, Tyne & Wear, UK.
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Re: Hameg HM307-3 Cleaning and Repair
I've checked all of the smoothing capacitors in the PSU (both HV and LV) and they are not leaky (Hunts tester) and show low ESR.
I tried the brightness setting procedure and the level of brightness did increase slightly. Unfortunately the trace is still barely visible in normal lighting. Lots of ripple I think! wme_bill suggested in post 46 that low CRT emission manifests itself as low contrast and blurriness. Despite being dim, the trace can be adjusted to be quite sharp! A glimmer of hope for the CRT? The ripple in the trace is another problem to diagnose. The main problem at the moment is the lack brightness from the CRT. I'll start checking the CRT circuit. Especially around the blanking circuit. What does this do? |
7th Jun 2019, 6:53 pm | #80 |
Octode
Join Date: Jul 2017
Location: Newcastle Upon Tyne, Tyne & Wear, UK.
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Re: Hameg HM307-3 Cleaning and Repair
The voltages measured on T352 (BF440 PNP) are all -870V. It tests good using the diode check on my DMM. With the component tester I get curious results. In my experience, if the tester shows anything but a transistor the transistor under test is bad. T352 could be the cause of the low brightness.
I'll have to look for a substitute. See attached photograph. |