Good Will GW Instek GDM-8045G multimeter

[anderoo]

Hi guys. I'm looking for a user/service manual for the Good Will / GW Instek GDM-8045G multimeter (pic below is not mine but same appearance).

I picked up one in a job lot that looks in good shape but I'd like to go through the cal procedure before trusting it.

I've checked the usual online manual repositories and also the GW website to no avail.

I did find the user/service manual for the very similar looking GDM-8145 (that manual is attached below) but I 'd like to get the correct manual for the older GDM-8045G because I suspect that there has been a board revision.

I'm hoping that someone has the PDF on their hard drive and can post it here for me.

Thank you.

[anderoo]

Since the user/service manual is elusive I thought it might help someone in the future if I posted any info that I have been able to find on this meter.

I found some pics on a Chinese language website of the internals and discovered that the multimeter chip set consists of the Siliconix LD120 and LD121A 4-1/2 digit A/D converter set.

In addition, the true RMS measurement capability is implemented with an Analog Devices AD536A True RMS-to-DC converter IC.

For ease of reference I've attached data for the AD536A and for the LD120/LD121A chip set, which I found in the 1985 Siliconix data book.

[anderoo]

Here is a link to that Chinese website which contains a repair blog for a trio of Good Will GW Instek GDM-8045G bench multimeters.

http://www.5bcl.com/Article/Print.asp?ArticleID=3297

In case that website goes down I've copied the board photos and partial schematics from that website to this post.

The main board is designated GDM-503C, and the display board is designated GDM-270D.

[anderoo]

A couple more photos of the main board are attached.

[anderoo]

Oh yes, I'm still looking for a proper user/service manual with the calibration procedure.

It should be easy to calibrate this meter - there's only 14 trimpots on the main board !!!

[coromonadalix]

to be on the safe side, i would measure ohms between the 3 pins of each trimpot and keep a note just in case ... sometimes you can sort in wich circuit they are used ... 1 trim dor each range  loll   14 trimpots is a lot but not uncommon,  on some eevblog threads there was an meter with literally tons of them ...