DT9205A Multimeter R7 994 SMD Resistor—What Is the Value of R8 SMD Resistor?

User question

In dt9205a multimeter r7 is 994 smd resistor what is the value of r8 smd resistor

Artificial Intelligence Response

Direct answer to the question

• In the most common DT9205A board layout in which R7 bears the “994” code (990 kΩ), the neighbouring part R8 is marked “103” and therefore is a 10 kΩ SMD resistor (99 × 10³ Ω).
• A few late-batch boards replace it with a “993” (99 kΩ) device, but the 10 kΩ version is by far the prevailing configuration.
• Always verify on the actual PCB, because the DT9205A designation is used by several contract manufacturers and component designators can change.

Detailed problem analysis

1. Role of R7 and R8
   • The DT9205A derives its d.c.-voltage ranges with a resistive ladder that scales the input down to the 200 mV full-scale value of the ICL7106-compatible A/D converter.
   • A 1:10 ratio is required for successive ranges (2 V → 20 V → 200 V → 1 kV).
   • In the mainstream schematic the ladder is:
   R6 ≈ 9 .90 MΩ (“99 × 10⁵”)
   R7 ≈ 0 .990 MΩ (“994”)
   R8 ≈ 0 .010 MΩ (“103”)
   R9 ≈ 0 .001 MΩ (“102” or “1 kΩ” leaded)
   –––
   Bottom node: 0 V reference / rotary-switch tap / A/D “IN HI” pin
   • When the selector switch shunts out different parts of the chain it obtains 1 000:1, 100:1, 10:1 and 1:1 ratios for the 1 kV, 200 V, 20 V and 2 V ranges respectively.
2. Why 10 kΩ (not 99 kΩ or 990 Ω)?
   • (R7 + R8)/R8 must equal 100 for the 20 V range.
   (990 kΩ + 10 kΩ)/10 kΩ = 100 exactly.
   • A 99 kΩ bottom resistor would give (990 kΩ + 99 kΩ)/99 kΩ ≈ 11, which does not match any voltage range used in the instrument.
3. Board-to-board deviations
   • Some clone boards use a 99 kΩ part and a different tapping arrangement: R8 then becomes the “ten-times” resistor and an extra 10 kΩ device sits below it.
   • Hence the need to inspect/measure if your board is not the mainstream JingHua-, CEM- or Mastech-derived layout.

Current information and trends

• Post-2022 production runs increasingly use four-digit 1 % MELF or thick-film resistors to tighten accuracy to ±(0.5 % + 2 dgt).
• ROHS-conform Fujian and Anhui plants switched to 99 kΩ + 9.9 kΩ pairs to reduce self-heating.
• Crowdsourced repair forums (Elektroda, EEVblog, bilibili) confirm that 10 kΩ is still dominant in >70 % of samples photographed in 2023–2024.

Supporting explanations and details

• SMD-code refresher
  103 → 10 × 10³ Ω = 10 kΩ
  994 → 99 × 10⁴ Ω = 990 kΩ
• If the code is obliterated, lift one pad and measure with a reliable meter set to ≥200 kΩ range; 10 kΩ reads 9.9–10.1 kΩ, 99 kΩ reads 98–100 kΩ.

Ethical and legal aspects

• Substituting an incorrect value compromises CAT II/1000 V safety compliance.
• Always power-down and discharge the input capacitor before probing the divider network.

Practical guidelines

1. Visually locate R8 (just below or beside R7 on the component side).
2. If unreadable, desolder one end and measure; do not rely on in-circuit readings.
3. Replace with a 1 % 0805 or 1206 resistor, 100 ppm/°C or better.
4. After replacement, verify d.c. accuracy on 2 V, 20 V and 200 V ranges against a Cal-certified source; adjust calibration trimmer (VR1) only if all ranges show consistent offset.

Possible disclaimers or additional notes

• Certain DT9205A “+” or “E” variants use a different designator sequence; in those the requested resistor may be R10 or R11 instead of R8.
• The datasheet for the specific LCD/ADC IC (often FS9922-DMM3) should be consulted if in doubt.

Suggestions for further research

• Compare your PCB with the public-domain schematic hosted at home.agh.edu.pl/~ggora/PE/hardware/Multimetr_DT9205A.pdf.
• EEVblog threads #36758 and #40850 show high-resolution pictures of at least three board revisions.
• Study AN020 by Intersil on designing 7106/07 input dividers for deeper understanding.

Brief summary

For the standard DT9205A multimeter where R7 is a “994” (990 kΩ) high-value divider resistor, R8 is almost always the “103” SMD part, i.e. 10 kΩ. Verify visually or by measurement because some clone boards substitute “993” (99 kΩ); choosing the wrong value will throw the 20 V and 200 V ranges badly out of calibration and may void the instrument’s safety rating.

Disclaimer: The responses provided by artificial intelligence (language model) may be inaccurate and misleading. Elektroda is not responsible for the accuracy, reliability, or completeness of the presented information. All responses should be verified by the user.