Analog multimeter repair on Ohm scale - UK Vintage Radio Repair and Restoration Discussion Forum

Malcolm T · 25th Jan 2024, 3:53 pm

I have replaced the 1.5v and 9v batteries but the meter still only reads 2.3 rds of FSD on X1k X10 and X1 ranges however on X10K it attains full FSD and beyond ie fully adjustable with the zero up pot, there is no visual damege to the components , very strange .
Does anyone have any suggestions as to a possible fault .

Malcolm T · 25th Jan 2024, 3:54 pm

2/3 two thirds FSD

Vintage Engr · 25th Jan 2024, 4:18 pm

Could we have the meter make/ model?

Malcolm T · 25th Jan 2024, 8:43 pm

HT -320 , that's all it states on the handbook, from memory it is circa early to mid 90s but would hazard a guess may be also late 1980s . will post a photo soon

stuarth · 26th Jan 2024, 10:03 am

IIRC, the HT-320 is a fairly generic Far Eastern analogue meter.

The lower 3 resistance ranges use only the 1.5V battery, the highest range uses the 9V and 1.5V in series. The obvious fault is a failing 1.5V battery or dirty battery contacts.

These meters have a universal current shunt, ie a string of resistors across the movement for the current ranges, and the resistance ranges tap into this resistor string. If one of the low value resistors at the lower end of this string has changed value (but not gone open circuit), it will affect high current and low resistance ranges without significantly affecting voltage, low current or high resistance ranges. Do you have a second meter to measure resistor values and to check all current ranges on the HT-320?

Stuart

Malcolm T · 26th Jan 2024, 12:19 pm

After thinking about this and staring at the 1.5v batteries and the compartment for some time it dawned on me what i may have done . It began a few years ago when i wanted to dispense with two 1.5v batteries and just use one 3v battery, so in my infinate wisdom i removed the two plastic moulding ends that formed the two AA battery holder as it had a horrible screw contact for the series connection .
I then installed a 3v Lithium battery AA into a soldered in holder to replace the two AA batts, but there was already a dodgy zero up pot as well that i ignored.
However reading the comments here i replaced the lithium AA with New Alkaline AA into two separate AA holders but rather stupidly connected them in parallel as per the Lithium single AA holder hence only getting 1.5v and not 3v into the meter, Re-wiring for series AA connection ie 3v the ranges came back to normal and can now zero up fully on all, however theres now the dodgy pot , it must need a switch cleaner clean out now . So i,m now a happy bunny.
My fault i,m afraid , lesson learned here.
Thanks for all the comments and help.
A valuable little meter saved.

25th Jan 2024, 3:53 pm	#1
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	Analog multimeter repair on Ohm scale I have replaced the 1.5v and 9v batteries but the meter still only reads 2.3 rds of FSD on X1k X10 and X1 ranges however on X10K it attains full FSD and beyond ie fully adjustable with the zero up pot, there is no visual damege to the components , very strange . Does anyone have any suggestions as to a possible fault .

25th Jan 2024, 3:54 pm	#2
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	Re: Analog multimeter repair on Ohm scale 2/3 two thirds FSD

25th Jan 2024, 4:18 pm	#3
Vintage Engr Heptode Join Date: Jan 2008 Location: Shrewsbury, Shropshire, UK. Posts: 852	Re: Analog multimeter repair on Ohm scale Could we have the meter make/ model?

25th Jan 2024, 8:43 pm	#4
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	Re: Analog multimeter repair on Ohm scale HT -320 , that's all it states on the handbook, from memory it is circa early to mid 90s but would hazard a guess may be also late 1980s . will post a photo soon

26th Jan 2024, 10:03 am	#5
stuarth Heptode Join Date: Feb 2010 Location: Heysham, Lancashire, UK. Posts: 669	Re: Analog multimeter repair on Ohm scale IIRC, the HT-320 is a fairly generic Far Eastern analogue meter. The lower 3 resistance ranges use only the 1.5V battery, the highest range uses the 9V and 1.5V in series. The obvious fault is a failing 1.5V battery or dirty battery contacts. These meters have a universal current shunt, ie a string of resistors across the movement for the current ranges, and the resistance ranges tap into this resistor string. If one of the low value resistors at the lower end of this string has changed value (but not gone open circuit), it will affect high current and low resistance ranges without significantly affecting voltage, low current or high resistance ranges. Do you have a second meter to measure resistor values and to check all current ranges on the HT-320? Stuart

26th Jan 2024, 12:19 pm	#6
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	Re: Analog multimeter repair on Ohm scale After thinking about this and staring at the 1.5v batteries and the compartment for some time it dawned on me what i may have done . It began a few years ago when i wanted to dispense with two 1.5v batteries and just use one 3v battery, so in my infinate wisdom i removed the two plastic moulding ends that formed the two AA battery holder as it had a horrible screw contact for the series connection . I then installed a 3v Lithium battery AA into a soldered in holder to replace the two AA batts, but there was already a dodgy zero up pot as well that i ignored. However reading the comments here i replaced the lithium AA with New Alkaline AA into two separate AA holders but rather stupidly connected them in parallel as per the Lithium single AA holder hence only getting 1.5v and not 3v into the meter, Re-wiring for series AA connection ie 3v the ranges came back to normal and can now zero up fully on all, however theres now the dodgy pot , it must need a switch cleaner clean out now . So i,m now a happy bunny. My fault i,m afraid , lesson learned here. Thanks for all the comments and help. A valuable little meter saved.