schlumberger 7150 - Page 1
Forum section: electronics / projects

author: comet2458
author_rank: Newbie
timestamp: January 21, 2013, 09:51:02 pm
content: Hi to alli have a schlumberger 7150 multimeter that,when powered up ..display and back light come on..but it resets itself constantly...checked power supply voltages....all seem ok.pulling hair out now,as not very good on the logic side of things...any help please on where to look/checkthanking in advancemick

author: ecat
author_rank: Frequent Contributor
timestamp: January 22, 2013, 09:45:34 am
content: Here are the user and maintenance manuals for the 7150 if you don't already have themhttp://www.ko4bb.com/manuals/index.php?dir=09%29_Misc_Test_Equipment/SolartronYou say it constantly resets, approximately how long between resets? Almost instantly or after a second or two or ...?The maintenance manual does mention two watch dog circuits, page 2.9 and page 2.12. A watch dog is a timer that runs independent of the processor, it is designed to force a reset if the processor should ever get into an unknown state. So, that is two 'official' reset options you can check, it's not much but at least it's a start.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 22, 2013, 12:30:17 pm
content: I have the same (Schlumberger/Solartron 7150 Plus). Great multimeters. They were made by Solartron in the UK which still provides maintenance and calibration services.If I remember right these resets can be caused if the front panel connectors don't have sufficient contact with their counterparts on the lower logic board. Remove the front panel and check/clean the contacts. Also, some of the ICs may be socketed (depending on the board revision I think), so removing and cleaning them may be another fix.BTW: one weak point in these multimeters (like in many other old test instruments) is the mains filter. The filter in the Solartron 7150 is made by the Swiss company Schaffner (model FN 372-2-21) and prone to bursting/exploding when getting old, which usually covers the electronics in some nasty aggressive gunk. Replacement parts are still made and are available from companies like Mouser and Farnell. Make sure you get a brand new filter (the current ones are made in Thailand IIRC) and not 'old stock' which is over a decade old and will probably fail quickly, too.

author: ecat
author_rank: Frequent Contributor
timestamp: January 23, 2013, 09:48:51 am
content: Quote from: comet2458 on January 23, 2013, 04:33:20 amJust to double check, it was doing this before you replaced the electrolitics?Have you tried the fix in Wuerstchenhund's post?The maintenance manual gives you the IC numbers and Pin numbers relating to the two reset circuits, best I can advise is sticking a scope on these pins to determine if the reset is caused by one of the watch dogs. Pay attention to the reset out of each watch dog AND the signal from the processor(s) that is supposed to reset the watch dog before the watch dog resets the processor.If the resets are not caused by the watchdogs you may have a problem with the power lines or something is drawing too much current. If the resets are caused by one of the watch dogs the problem is either associated with 'something' the processor(s) is reading, with the firmware itself - bad EEPROM, with one of the processors or maybe bad data in the non-volatile EAROM. All guess work of course.

author: ecat
author_rank: Frequent Contributor
timestamp: January 23, 2013, 06:00:37 pm
content: TP8 is the A15 address line of the logic side processor, it maps to the $8000 address range and appears to act as the chip select for IC508 EPROM (program storage prom).http://www.datasheetarchive.com/TMS2564-datasheet.htmlSo, if TP8 is high and E is high the output of the following NAND gate (IC515 a) is low and IC508 is selected, all this means is that the processor is reading from the EPROM. When you say it looks good do you mean it is high or low or ...? I would be surprised if it was high for 7 seconds as this would mean 7 seconds of purely eprom access, no ram, no other I/O etc. I'm not surprised it drops low on reset, but I'm open to correction.I suspect the relay is just a symptom, on power on say it starts open then the cpu takes control and closes it then a reset happens and it opens again etc.What can you tell me about IC510 pin 6 (!Reset) this should connect directly to TP3, also IC507 pin 1 (WD reset) and pin 8 (WD clock)?Also IC103 pin 6 (reset) and IC11 pin 1 and pin 9, IC108 pin 1 (connects to TP1), pin 8 and pin 12? I'm also curious about IC108 pin 13 which looks like part of a RC network.btw, I have very little digital and no analogue, lol, but I do have a 7150 plus which is why I had the documentation to hand. Maybe we can muddle through this despite the odds

author: ecat
author_rank: Frequent Contributor
timestamp: January 23, 2013, 09:55:16 pm
content: Interesting stuff.5.98v looks a little high but let's ignore that for now.IC103 is the processor on the floating side, if pin 6 is always low then the processor is permanently held in reset, it cannot run. This cannot be a good thingIC108 should be raising the reset line but it can only do this when it is set into count mode - I'm guessing here. To enter count mode pin 1 must be high, I'm worried when you say it is always 0.Thinking a bit more clearly we may have a problem here. So far all your measurements on the floating board, 103, 11, 108, have read as 0V. The whole idea of the floating board is that it does not share a ground with the logic board or the mains earth. If you have your scope ground connected to 0V on the logic board while probing the floating board you do not have a circuit to measure. What I don't know is what happens if you connect the scope ground to the 0V of the floating board, you will be pulling the floating ground to mains earthand I cannot tell if this is a bad thing(1). We need proper advice on this. Of course, if you've already tried connecting the probe ground to floating 0V then let me know and we'll go from there.What I would do in this case is use my multi-meter for measurements on the floating board and hope I didn't need to measure any fast signals. First measure across the floating 0V and 5V line with your meter to give us an idea of what logic high looks like. Now when measuring we are looking for 0V (low), something close to 5V (high) and anything that lies in between or causes the reading to fluctuate we can assume is a digital signal.Using the meter, repeat the 103, 11 and 108 measurements.Back to the scope what is IC515 pin 10 (or IC510 pin 12, they are connected) doing. This the data transmit from the earthy cpu to the floating cpu which also acts as a reset clear for the floating cpu.Edit:(1) The schematic shows the 'Lo' terminals both front and rear connect directly to the floating 0V, from this I'm 99% certain that connecting a scope probe ground to floating 0V will be okay. Unless anyone knows different?

author: ecat
author_rank: Frequent Contributor
timestamp: January 24, 2013, 10:10:44 am
content: Some data sheets for anyone playing at home:IC11http://www.datasheetarchive.com/SN74LS175-datasheet.htmlIC107http://www.nxp.com/documents/data_sheet/HEF4040B.pdfIC108http://www.datasheetcatalog.org/datasheet/motorola/SN54LS197J.pdfI've edited my previous post, I'm fairly certain you are ok connecting the scope probe ground to floating 0V, the choice is yours. Remember, I don't do analogue.Right, back to business.IC103 pin 6, it is going high so the floating cpu can run and it looks like IC108 is doing something reasonable.IC515 is exciting news - seriously. This shows the earthy CPU is trying to talk to the floating cpu, this is also the first unequivocal proof we have of the earthy cpu running.Now to check if the floating cpu is responding. What is IC518 pin 6 up to? Also IC510 pin 11?

author: ecat
author_rank: Frequent Contributor
timestamp: January 24, 2013, 03:01:02 pm
content: IC508 is the main eprom, pin 6 is the address line A4, it's nice to know this is changing as the cpu runs through the code but not really relevant just nowIC510-11 is the earthy cpu's serial RX pin, this is connects to the opto-coupler IC518 pin 6 via an inverter. What you should see here is something like the 'colour bar signal' as you described it when looking at IC510-12.The way I think of it: A wiggly line comes out of the earthy cpu IC510-12 (Tx) and crosses through pin 3 of the connector to floating cpu IC103-11 (Rx). If everything is working another wiggly line should come out of IC103-12 (Tx) and cross through the connector pin 2 back to the earthy cpu IC510-11 (Rx). Yep, serial communications are all about wiggly linesSo, IC510-12 should be the same as IC103-11 and this is IC510 talking to IC103. IC103-12 should be the same as IC510-11 and this is IC103 talking back to IC510. In both cases you should see wigglies.I tried to add an attachment then lost my post, I'll try again

author: ecat
author_rank: Frequent Contributor
timestamp: January 24, 2013, 05:41:04 pm
content: Okay, so we definitely have two way communication. Good news, both cpus must be running and their proms are at least partially ok. Bad news, I don't really know where to go from hereWe shouldn't be getting 6V from a 5V regulator, maybe it's a ground/floating ground artefact but well worth checking through the v-regs again.I cannot think of a way to determine if the resets are from the watch dog(s) or some power issue. I don't know if you can scope a reset line and the supply lines at the same time? If you have a digital scope this is worth looking into.I'll have to check how many connectors we have to play with. For now you could try disconnecting the keyboard then powering on to see if the symptoms change. Reconnect the keyboard and disconnect that 4 pin connector shown in the previous attachment, switch on again and look for any changes.When the unit is powered on it comes up in Volts mode? Whatever mode it does come up in could you try quickly selecting some other mode - amps, ohms and again note any changes. The reason for this is to test out the 'drift compensation' which should run every 10 seconds but will be force to run whenever there is a mode or range change.It's also worth checking the continuity of any cables and their connectors.The switches on the back:You can try switching GPIB on and check the display. Leaving it on try 'Talk Only' on and check the display. Turning 'Talk Only' off, switch 'Listen Only' on and check the display. Switch GPIB back off for normal - haha - stand alone operation.

author: ecat
author_rank: Frequent Contributor
timestamp: January 24, 2013, 11:26:38 pm
content: You're welcomeInteresting thing about those voltage measurements, they are all out by about 20%. Another meter with a problem?I would try running through the points in my previous post.You could also think about forcing the cpu's reset pins high: lift the pins clear of their sockets, pop IC517 and IC108 out of their sockets if they are socketed or some other way of isolating them, then connecting the reset lines to the 5V supply via, say, a 1k resistor - this will certainly take the watch dog resets out of the equation. Expect one of three results, everything works (unlikely), the meter still resets (power problem), the meter locks up (ie the watch dogs were doing what they were designed to do and we need to find whatever it is that's causing one or both of cpus to lock up)The trouble from here on in is the risk of cooking the little beast before we can fix it. Let me sleep on it.Edit:I'll put this link here in case anyone should need it....http://www.perdrix.co.uk/Solartron7081/index.htmRight down at the bottom of the page is the image for the eprom on the earthy board.

author: ecat
author_rank: Frequent Contributor
timestamp: January 25, 2013, 10:19:23 am
content: Solartron UK? That's easyhttp://www.solartronmetrology.com/about/contact-solartron-metrology.aspx

author: ecat
author_rank: Frequent Contributor
timestamp: January 25, 2013, 12:58:18 pm
content: I dug out my 7150 Plus which I think in many ways is very similar, if not almost identical to the straight 7150. A power on the display shows all segments for about a second, the display clears and the word PASS is shown for about a second (self test complete I guess), then if GPIB is on the display shows IEEE nn. After all of that I get the Auto and data display.So, your 7150 is possibly failing self test? The Plus will display a number of fail messages relating to self test but I don't know if the same applies to your beastie. Also, it's software and no software written can account for all possible fail modes, lock up and loop is not an unusual fail mode.Glancing through the Plus service manualhttp://www.ko4bb.com/Manuals/09%29_Misc_Test_Equipment/Solartron/Solartron_Schlumberger_7150_Plus_Service_Manual.pdfthere are a few interesting notes:Page 3.4 section 5.1 Power supply tests. Voltages should be within 5% !Page 6.3 Check list. Nice to have if the messages are relevant to the 7150. I especially like the prom and ram fail messages if they work as advertised.Page 6.4 section 3 tests on the earthy pcb. Well, we took the long way around but we've covered all except 2. Worth a look.Page 6.5 section 4 tests on the floating pcb. Again we took the scenic route to half of this. 2 and 5 are worth a look.Assuming the above check out okay my next move would be a scope probe on the reset line and a second scope probe on one of the $0000, $1000, $2000, $3000, $4000, $5000, $6000, $7000, $8000 lines to see which of lines is asserted at or nearest to the point of reset. This is easy with a logic analyser, I'm guessing it is doable with a dso?