Brymen BM869S - OL problem with AC measurement

[soesante]

Hi,
I got problem with my BM869S that show OL in AC measurement, when start up the DMM and even with the lead disconnected.

it just OL and unable to measure AC voltage from main outlet,  but the frequency measuring correctly 50 Hz
(I attached the Pic)

I don't know where to start probing for the problem. 

I found one post said that it could be RMS - DC module problem AD636J
and so I order this module - Now new module is arrived but still Im not so confident to replace it.
Since It just based on quest.
I can not prove it by measuring the circuit e.g. voltage or else to locate the real problem.

FYI. I can't see any phisical damage component visually and I did measuring to some of component but can not find any indication of damage component.
So I think there is in circuit problem when power on.

Is anyone can help to guide me to indicate how I should start to measure.

 

 

[coromonadalix]

what equipment do you have ?   desoldering pump,  hot air desoldering tools,   copper wick ?   do you know someone who is good in electronics ?   if you dont have much experience you may cause more damage than repairs ?

[castironman]

Sorry, but do you have the same result if you turn the knob for next Vac selection ? I just want to rule out the vfd part of where you are now.
Thank you.

[joeqsmith]

Sorry, but do you have the same result if you turn the knob for next Vac selection ? I just want to rule out the vfd part of where you are now.
Thank you.

And AC+DC..  Also different ranges.  Maybe they only have the AC line for a signal source. 

Meter looks very dirty.  Note the missing bands on the front end resistors.  Perhaps having a rough life. 

[soesante]

Hi, just got a chance to response.

@ castironman,
All AC measurement got the same problem when I turn the knob.
other measurement e.g DC, Ohm, Diode mode, Caps, AMP. is working fine.
AC+DC only measure the DC part, While AC show OL.

@coromonadalix and joeqsmith,
I have all the equipment you mention, incuding Osciloscope and Function Generator.
as hobbies I did repair some LCD, PSU, Microwave controller board,etc. and yes this trusty meter has been through a rough life with me for all those troubleshoting things. until suddently it stop measuring AC. 
Problem is because I don't have schematic of this DMM and I dont quite understand where to start troubleshoting DMM.
if you can give me some advise - appreciate it.

[Chris56000]

Hi!

I can!

Examine the devices used in your Brymen Meter carefully and locate the A/D converter and display driver – most modern DMMs use a single large QFP device but there are a few two–chip solutions in use!

Once you know what chip the A/D and DVM is, download its datasheet and study it carefully – most of these modern meters are based on the Chip Maker's suggested application circuits!

You want to identify the Input High and Input Low pins and short these with a resistor of about 1k or directly – if the A/D is in order the display should read zero or close to it – if you still get 'OL' with the input pins shorted or linked by a resistor, there is a fault in the DVM circuit itself, possibly a reference voltage fault or an internal fault in the chip itself!

If you do get a zero reading when the DVM ic inputs are shorted the fault is in the AD636 circuitry or further back in the voltage–dividers & swiching and you need to check it's d.c. output voltage – the datasheet for the AD636 gives example applications with the scaled output the circuit suggestions are for!

Also don't forget to check the impedance across the V I/P and COM terminals – most reputable DMMs will read about 10–12 Megohms – anything much higher suggests damaged input components or divider network (or even spidery bits of print in the input circuits!), whilst much lower suggests a protective diode, etc., may be s/c!

Have a prod round with some chip paperwork printed out and another good meter and hopefully something will come to light – post back if still stuck!

Chris Williams

[t1d]

I doubt this has anything to do with it, but check all of the fuses. I recall that some functions will still work, with one blown. If you do have a blown fuse, be very careful to replace it with a genuine, OEM fuse. There are a lot of fakes out there.

[Chris56000]

Hi!

Further to my previous post, Brymen use a proprietary device called the BTC AD-85-4 device apparently made by them as the A/D converter and there's zero info as to it's pin-out, altho' a search on this forum will find lots of information on the 121GW EEV Blog Multimeter which is also made by Brymen and has schematic info. available, but I couldn't find a link to it in all the rambling nonsense!

However there's a possibllity you might be able to use the datasheet for the Fortune FS970X https://www.ic-fortune.com/upload/Download/FS970X-DS-44_EN.pdf - there's a chance the pin-outs of the AD-85-4 in your BM-869S might be similar!

Unfortunately I don't have one of these meters myself and can't afford one so I can't offer more concrete practical help I'm afraid!

Chris Williams

[coromonadalix]

The 121gw doesn't use the same meter chip, its an hy3131, it wont be of any use, its the 235 who is an collaboration between eevblog and Brymen.

Ask Brymen for pinout / schematics  under non disclosure, had to do it for my 857s to obtain the "how to calibrate my meter, enter cal mode"  they were helpful.

[t1d]

This DMM is also branded by Greenlee Tools (DM860A?) and (I think) AmProbe. Confirm those manufacturer model numbers and maybe you can widen your search.

[Ordinaryman1971]

Brymen is sold as Greenlee, Amprobe is Fluke's offspring.
I think i have this meter in both flavors. Let me know if I can help and I will measure what you need.
Great meters by the way. I mostly use 200 and 500 series, they are smaller, the 800 series is a serious piece.... massive, great back light on display. The only con I can find is that when you measure diodes... it doesn't beep the same way Fluke does, so you have to look at the screen. the other thing is that measurements are just a tiny bit slower, but it's just a blink of the eye slower. Higher models have increased accuracy and digit count... I would compare them to Fluke 189.
Dual screen for measuring AC and DC, two temp probes, again on higher models... really really good gear it is.
And the probes that Brymen includes with those meters are one of the best I've ever got with any meter.
Basically, solid and very reliable multimeter, by my standards, everybody should have one.... or five, pretty colors too, great red on Brymens, and forest green on Greenlee.... and blue on eevblog version, lets not forget about the blue one.