ESCORT 97 multimeter - schematics and repair help

[perithess]

Hello everyone,
I own quite a few years now an ESCORT 97 multimeter (sounds like car name) and also the company that I am working owns a dozen of ESCORT 97s, about ten ESCORT 98s and a couple of ESCORT 99s. All of them have been great and accurate multimeters for the time and we mostly use them for data logging. They were very reliable the last decade of use and they are usually pass the annual calibration verification with very good measurements.
But the last two yeas my private ESCORT 97 and a couple of 97s at work failed. I am trying to find out any schematics or service information in order to repair them.
Can anyone help me to repair this multimeters?

[lowimpedance]

In what way has it failed ?. Which measurements and/or Ranges or its completely dead. More detail including internal pictures which might give a clue to the chip set used and thus a data sheet may exist which will most likely be more possible than finding a schematic. This is generally the case with these old Escort meters.

[perithess]

In what way has it failed ?. Which measurements and/or Ranges or its completely dead. More detail including internal pictures which might give a clue to the chip set used and thus a data sheet may exist which will most likely be more possible than finding a schematic. This is generally the case with these old Escort meters.

My multimeter had an intermittent failure to start. One of my colleagues poked it and burned the regulator stages. According to my assumption there are two negative regulators which make the 9v +5v and -5v and I replaced them with nju7211u50 and now is power up ok. But the measurements are multiplied by 10. When I am measuring 10v it shows 100v on the screen. In mV overanges on the x10 value also. Apart from that I haven't test it more. I have tried to repair it by replacing all the chips on analog board. The adc is the max131 and the CPU is an escort part. I will upload photos later.

[Electro Detective]

I still have an older Escort, my first decent TRMS meter and still kicking strong   

I think Escort are now owned by Keysight and some of the Escort meters are rebadged as Keysight                   and painted ORANGE 

Perhaps Keysight may have some service docs ?    

Good luck with it   

[lowimpedance]

Can you set a manual range and have the decimal point display in the correct position then apply the 10V and see if the meter overloads or what value is displayed.

[perithess]

I have set the range 1 (4V full scale normally) manually in order to measure an AA battery (1.5v) an the meter overflowed. I the set the range 2 (40v full scale normally) and showed 15v. The same happens either in 4000 or 40000 count mode. Does anyone know any button combination that changes settings? The adc is max133 and CPU is a custom chip  2270 escort 39-25765-1a. The wires and the capacitor are for faster test. I have replaced almost all the ics on the bottom board and a lot of them on the top board. When I hold the peak (green) button during startup it shows the following message (CHEEP).
Thanks for your answers.

[lowimpedance]

 Have you replaced the max133 ? Digikey have it (exact footprint to be checked of course). As it seems to be responsible for the auto ranging. Go through the data sheet carefully and see how its applied in your unit as this is probably as close to a schematic you will get with this meter. My best guess would be a gain stage around the ranging is stuffed and most likely its the 133. Also check all passives around it first.
 Do you think its worth it or is it time for something new (Christmas and all  ), Good luck either way.

And That 'CHEEP' display .................was the firmware guy taking the piss I wonder !.

[perithess]

I have replaced the max133 but with no luck at all. I have checked the sample designs for this adc and they are not very common to the applied circuit. My last try to ask here for help was in order to find some 'internal' info for this multimeter that will help me and have not been published yet. At the moment its worth to repair it because they are part of an automated measurement system that is not worth to redesign it. I will check again the range switching system. Does anyone know how was calibrated this multimeter?

[lowimpedance]

I think the best approach would be measurement comparison with a working unit ,in particular around the max133 and the range switching.
No idea how cal was done, sorry.

[texaspyro]

If you look towards the back of your local "alternative" newspaper there are lots of ads for escort service places.  I assume they fix multimters... what else could they be?   

I'll get my coat...

[perithess]

I didn't understand your post because English is not my mother tongue. I did contact 2 external service places but they charge an arm and a leg. If anyone knows a multimeter that uses the max133 and there is a schematic availiable please post it.

[texaspyro]

I didn't understand your post because English is not my mother tongue.

In the US an "escort service" is where you can hire "women of negotiable affection" for an evening out on the town, etc.  They tend to advertise their "services" in rather sleazy newspaper advertisements... there tends to be many pages of their advertisements.

[HpMad]

This multimeter Escort 99 is the same as keysight 1252a they acquary the company and now is part of keysight, maybe this post is very outdated but i want to comment out anyway.
the escort 97 should be agilent 1241a.

[barijan]

...The adc is max133 and CPU is a custom chip  2270 escort 39-25765-1a...

I know it's an old thread, but here's some information that might be useful for the fellow forumers.
This "custom" Escort chip is actually a regular Samsung KS57C2016 microcontroller.
The actual custom stuff is the firmware, that is pretty obscure. So, there's no use replacing the chip without coding it properly.

BTW, Hioki has rebranded this line as well as the Hioki 3800 series (3801, 3801-50 and 3802).

Here's the KS57C2016 datasheet.
https://www.datasheetarchive.com/pdf/download.php?id=6fc2a8add4ca52193bdab3f5e723d108cccbea&type=O&term=samsung%2520KS57C2016

[shakalnokturn]

Adding my brick to this piece of archaeology, there's very little information on them on internet may as well keep things together...

I now own 2 of these meters, I consider them very good for their age.

The big downside for me is that they don't power to their last display settings including 40k count mode.

I have dumped the contents of my EEPROM before fooling around, considering the possibility of gaining model 95 software functions. (Anyone have clues looking at the dump?)


After a few hours looking at Agilent service manuals, pushing butons (I don't think Escort 97 is same as Agilent 1241A) I finally found how to get into calibration menu:

Turn on to any function while holding "Hz", release "CHEEP" is displayed.

Press "PEAK" (Blue/Green) + "DUAL" simultaneously > 1s.

Turn selector to function that needs adjustment, DMM displays -rdY- on secondary display, main display prompts for the reference input needed (mostly tens of 3.2 whatever).

If only one range in a function needs readjusting set required one by using "RANGE"

Oh crap! No 3.2x10^x whatever at hand?
Nevermind, one can set a different reference value by using "DH" (Hold) and "REL" keys.

Connect required reference then press "DUAL", secondary display displays "CAL0" then some figures (not certain what they are), there's a few seconds delay, if DMM is happy it moves on to next range, if reference is too far from requirements (or DMM at fault) you get a "E-00x" error code.

After the highest range secondary display gives you a "PASS", adjustments are written to EEPROM as long as there is no error code even before highest range, no need to go through all the ranges, a single range can be adjusted, then multimeter power-cycled.


Mr Kardacz, if your lurking in here please get lost.

[perithess]

Thank you very much for your help.
I tested on the fly the procedure and calibrate some functions and worked fine.
Now I need to setup my calibration equipment to perform a full calibration.
Do you know any other functions that you can perform through this calibration menu?
Maybe there is a load default setup?
Anyway, I can confirm at least the memory chip was bad and the replacement needs reprogramming.

Your help is greatly appreciated.

[shakalnokturn]

I didn't expect to hear from you, thought the multimeter would have been long gone since 2017. Pleased it helped.
I'm not aware of any other tweaks in this mode, I haven't really searched though. Looking at service manuals for Escort designed Agilent models may give some hints if there is anything else to be found.

I'm curious to know how adjustment goes with a blank EEPROM, considering the DMM gives you an error if there is too much difference between requested and actual input.
Im not sure what the requested vales are referenced to: Could be ROM defaults written (or not) to a blank EEPROM, if the reference is meant to be current EEPROM values you may have to write my dump before adjustment. (In any case it could save you time if you first do a performance check as per the Agilent procedures.)

I've readjusted the full ACV on mine after replacing an electrolytic in the RMS section, I'll re-dump to get a vague idea of memory organisation.
Then if I'm courageous enough I'll give it a blank see if it writes defaults and if that gives me any clues to how it identifies as a 97 or 95. (Were they were a joint venture between Ford and Saab ? )

[shakalnokturn]

Back to answer most of my previous questions...

After giving it a blank EEPROM it will measure, however values are quite off and the decimal is misplaced displaying about 10x the input.

Adjustment mode will work just fine, here I grossly calibrated the 4V and 1kV ranges (to get an idea where DCV trims are stored). On exiting, decimal was correctly placed for readjusted ranges, others remained false.

I was thinking that the model 95 had more features than the 97, it seems I've been fooled by the table in last attachment that must be wrong.

Perithess, you've waited 5 years, now you have no excuse... 

Attached images:
1st comparison showing where ACV adjustments are stored.
2nd test with blank EEPROM.
3rd miss-leading table?