Polar Instruments TONEOHM 950 User manual

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Polar Instruments Ltd.
Garenne Park
St. Sampson
Guernsey
Channel Islands
GY2 4AF
ENGLAND
http://www.polar.co.uk
Fax: [phone]
Email: m[email protected]
MAN130–2011
TONEOHM 950
SERVICE
MANUAL

TONEOHM 950 SERVICE MANUAL
POLAR INSTRUMENTS LTD. HARDWARE WARRANTY
1. Product Warranty. Product hardware is warranted to be free from defects in material and
workmanship during the Warranty Period (as defined below). Product hardware is warranted to
conform substantially to Polar’s then current (as of the date of Polar’s product shipment)
published user documentation during the Warranty Period. The Warranty Period is twelve (12)
months. Product support beyond these periods may be available at additional cost – consult Polar
for details.
2. Warranty Claims. Polar shall incur no liability under this warranty if the end user fails to provide
Polar with notice of the alleged defect during the applicable Warranty Period and within seven (7)
days of delivery to end user or, if the defect would not have been reasonably apparent on
inspection, within seven (7) days of its discovery by end user. After receiving such notice, Polar
will notify the purchaser of its designation of one of the following problem resolution methods:
Return to Factory: The allegedly defective goods must be returned to Polar within seven
days of Polar’s notice and in accordance with Polar’s instructions advised at the time.
Other: Polar will use commercially reasonable efforts to repair, correct or work around
the problem by means of telephone support or other means reasonably determined by
Polar.
Polar shall incur no liability under this warranty if Polar’s tests disclose that the alleged defect is
due to causes not within Polar’s reasonable control, including alteration or abuse of the goods.
Under the Return to Factory alternative, if a Product is determined not to be defective or to have a
defect due to causes not within Polar’s reasonable control, Polar reserves the right to apply a
processing charge.
3. Damage in Transit. End user must notify Polar and the carrier of any claim for damage in transit
within two (2) days of receipt of the damaged merchandise. Failure to do so may result in the
carrier and/or Polar refusing to accept liability in which case end user must pay the purchase price
as if the hardware had been delivered without damage.
4. Polar’s Liability Polar’s liability, and end user’s sole and exclusive remedy, shall be limited to the
express remedies set forth in this Polar Hardware Warranty.
5. Disclaimer of Warranties. POLAR MAKES NO OTHER WARRANTIES, EXPRESS, IMPLIED
OR STATUTORY, REGARDING PRODUCTS. ALL OTHER WARRANTIES AS TO THE
QUALITY, CONDITION, MERCHANTABILLITY, FITNESS FOR A PARTICULAR PURPOSE,
OR NON-INFRINGEMENT ARE EXPRESSLY DISCLAIMED.
6. Limitation of Liability. POLAR SHALL NOT BE RESPONSIBLE FOR DIRECT DAMAGES IN
EXCESS OF THE PURCHASE PRICE PAID BY THE END USER OR FOR ANY SPECIAL,
CONSEQUENTIAL, INCIDENTAL, OR PUNITIVE DAMAGE, INCLUDING, BUT NOT LIMITED
TO, LOSS OF PROFITS OR DAMAGES TO BUSINESS OR BUSINESS RELATIONS,
WHETHER OR NOT ADVISED IN ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES,
THE FOREGOING LIMITATIONS SHALL APPLY, NOTWITHSTANDING THE FAILURE OF
ANY EXCLUSIVE REMEDIES.

DECLARATIONS
v
DECLARATIONS
European Community Directive Conformance Statement
Refer to the Operator Manual to determine conformance with European
Community Directives.

TONEOHM 950 SERVICE MANUAL
vi
SAFETY
WARNING The service instructions contained in this manual are for use
by qualified electronic service personnel only.
WARNING
The LIVE and NEUTRAL lines on this unit are BOTH fused.
When the unit is connected to its supply, the opening of covers or removal of panels is likely to expose
dangerous voltages.
GROUNDING
This unit must be earthed (grounded); do not operate the instrument with the safety earth disconnected.
Ensure the instrument is connected to an outlet with an effective protective conductor terminal (earth). Do
not negate this protective action by using an extension cord without a protective conductor.
Note: This instrument is fitted with 3-wire grounding type plug designed to fit only into a grounding type
power outlet. If a special local plug must be fitted to the power cord ensure this operation is performed by
a skilled electronics technician and that the protective ground connection is maintained. The plug that is
cut off from the power cord must be safely disposed of.
Power cord color codes are as follows:
Europe
brown live
blue neutral
green/yellow earth (ground)
United States
black live
white neutral
green ground
POWER SUPPLY
Check that the indicated line voltage setting corresponds with the local mains power supply. See the rear
panel for line voltage settings. Instruments with a serial number prefixed with a letter (e.g. A1234) are
configured for 90 – 110 Volts only.
Changing the line voltage settings on this instrument must only be performed by a skilled electronics
technician. Instructions for changing the line voltage settings are contained in Section 5.

SAFETY
vii
OPERATION
This manual contains instructions and warnings which must be observed by the user to
ensure safe operation. Operating this instrument in ways other than detailed in this
manual may impair the protection provided by the instrument and may result in the
instrument becoming unsafe. Retain these instructions for later use.
The unit is designed for use indoors in an electrical workshop environment at a stable work station
comprising a bench or similar work surface.
Use only the accessories (e.g. test probes and clips) provided by Polar Instruments.
The instrument must be maintained and repaired by a skilled electronics technician in accordance with the
manufacturer’s instructions.
If it is likely that the protection has been impaired the instrument must be made inoperative, secured
against unintended operation and referred to qualified service personnel.
Protection may be impaired if, for example, the instrument:
•Shows signs of physical damage
•Fails to operate normally when the operating instructions are followed
•Has been stored for prolonged periods under unfavourable conditions
•Has been subjected to excessive transport stresses
•Has been exposed to rain or water or been subject to liquid spills
CAUTION
Electrical Isolation
Always disconnect the board under test from the local mains supply (including ground) before using this
instrument.
Static Sensitive Devices
This unit contains Static Sensitive Devices. Static discharge can damage some electronic components.
Care must be taken when handling these components. Observe appropriate precautions to avoid damage.

TONEOHM 950 SERVICE MANUAL
viii
SPECIFICATIONS
Track Resistance
RANGES [Ω], 200mΩ, 2Ω, 200Ω, 20KΩ. Instruments with serial numbers below
005975 have a 2KΩrange instead of 200Ω.
ACCURACY ±6% in 200mΩ, ±5% in 2Ω
±4% in 200Ω, ±5% in 20KΩ
[Ω] RANGE High sensitivity, uncalibrated.
Approximately 40mΩfull scale.
PROBE VOLTAGE 60mV maximum.
INDICATION Tone and meter in all ranges.
PROBE PROTECTION Momentary contact up to 250V.
Track Current
RANGES 200mA, 2A, TRACE.
ACCURACY ±15% in 200mA, 2A for track resistance between 25mΩand 500mΩ.
Reading proportional to current when UNCALIBRATED LED is lit.
UNCALIBRATED LED lit during ranging.
Reading in TRACE is proportional to detected magnetic field strength.
TRACE SENSITIVITY Capable of detecting current flow with 200Ωresistance across Drive
Source.
PROBE VOLTAGE 600mV maximum in 200mA, 2A.
Not applicable in TRACE.
INJECTION CURRENT 250mA maximum.
Not applicable in TRACE.
INDICATION Tone and meter in all ranges.
PROBE PROTECTION Momentary contact up to 250V in 200mA, 2A.
Not applicable in TRACE.
Track Voltage
RANGES 2mV, 20mV, 20V.
ACCURACY ±4%, ±15µV.
INPUT RESISTANCE 120Ωin 2mV, 20mV.
1MΩin 20V.
INDICATION Meter in all ranges. Tone in 2mV, 20mV.
PROBE PROTECTION Momentary contact up to 250V in 20V.
30V in 20mV, 2mV.
Plane Shorts
INDICATION Tone, uncalibrated meter and fault direction arrows.
SENSITIVITY Adjustable for differing plane resistance. Capable of detecting shorts
up to 20Ω.
Plane Stimulus
OUTPUT VOLTAGE 550mV maximum. Active only when PLANE SHORTS is ACTIVE and
outputs are connected to a plane.
OUTPUT CURRENT 700mA RMS maximum.
PROTECTION Each output separately fused (5A Fast).

SPECIFICATIONS
ix
Drive Source
OUTPUT VOLTAGE 0 to 550mV, adjustable.
AC in TRACE, DC in all other ranges.
PROTECTION Protected to ± 30V.
ENVIRONMENTAL OPERATING CONDITIONS
The instrument is designed for indoor use only under the following environmental conditions:
Altitude Up to 2000m
Temperature +5°C to +40°C ambient
Relative humidity RH 80% maximum at 31°C — derate linearly to
50% at 40°C
Mains borne transients As defined by Installation Category II
(Overvoltage Category II) in IEC664
Pollution Degree 2 (IEC664)
Power Requirements
230V ± 10%, 115V ± 10% or 100V ± 10% at 50/60Hz, 25VA.
Fuses
Below Serial Nº. 11244
One fuse 230V 160mAT
115V 315mAT
Serial Nº. 11265 – 12212
Two fuses as above
Serial Nº. 12213 up
230V 125mAT
115V 250mAT
Physical characteristics (excluding accessories)
Dimensions 305mm (12 in.) wide.
150mm (5.9 in.) high.
275mm (10.8 in.) deep.
Weight 3.5 kg.
Flammability Enclosure to UL94 V-0.

TONEOHM 950 SERVICE MANUAL
x
SYMBOLS
REFER TO MANUAL These sockets are for connecting only Polar Instruments probes and
connectors for use as described in the Operator Manual. To prevent
damage to this product and to ensure its safe use observe the
specifications given in this manual when connecting to terminals
marked with this symbol.
ACCESSORIES
Standard Accessories
Needle Probes ACC152
950 Plane Probe/Clip assembly ACC113
950 Current Trace Probe assembly ACC114
950 Stimulus Lead (Set of 4) ACC134
Lightweight Headphones EPM115
Optional Accessories
Bare-board Stimulus Lead set (0.025") ACC121/XG25
Bare-board Stimulus Lead set (0.031") ACC121/XG31
Bare-board Stimulus Lead set (0.040") ACC121/XG40
Bare-board Lead set (universal) ACC154
Service Manual MAN130

CONTENTS
xi
CONTENTS
DECLARATIONS.......................................................................................................................................... v
European Community Directive Conformance Statement .....................................................................v
SAFETY....................................................................................................................................................... vi
WARNING.................................................................................................................................................vi
GROUNDING............................................................................................................................................vi
POWER SUPPLY .....................................................................................................................................vi
OPERATION............................................................................................................................................vii
CAUTION.................................................................................................................................................vii
Electrical Isolation.............................................................................................................................vii
Static Sensitive Devices.......................................................................................................................vii
SPECIFICATIONS..................................................................................................................................... viii
ENVIRONMENTAL OPERATING CONDITIONS.....................................................................................ix
Power Requirements.............................................................................................................................ix
Fuses.....................................................................................................................................................ix
Physical characteristics (excluding accessories) ..................................................................................ix
SYMBOLS................................................................................................................................................. x
ACCESSORIES ........................................................................................................................................ x
Standard Accessories ........................................................................................................................... x
Optional Accessories............................................................................................................................. x
SECTION 1 PERFORMANCE CHECK.....................................................................................................1-1
MAINTENANCE AND CALIBRATION OF INSTRUMENTS..................................................................1-1
Performance Check ...........................................................................................................................1-1
Adjustment Procedure........................................................................................................................1-1
Recommendations for Routine Maintenance.....................................................................................1-1
PERFORMANCE CHECK......................................................................................................................1-2
Equipment required............................................................................................................................1-2
Procedure...........................................................................................................................................1-2
SECTION 2 – ADJUSTMENT PROCEDURE ...........................................................................................2-1
ADJUSTMENT PROCEDURE...............................................................................................................2-1
Equipment required............................................................................................................................2-1
Display Calibration..............................................................................................................................2-1
A2D Calibration ..................................................................................................................................2-1
Resistance Calibration .......................................................................................................................2-1
Current range adjustment ..................................................................................................................2-2
Current offset calibration — Version 8 firmware and above...............................................................2-2
Current Trace.....................................................................................................................................2-2
Plane Shorts.......................................................................................................................................2-3
SECTION 3 – CIRCUIT DESCRIPTION....................................................................................................3-1
TONEOHM 950 THEORY OF OPERATION. ........................................................................................3-1
Main Operating modes.......................................................................................................................3-2
Track resistance.............................................................................................................................3-2
Track Current .................................................................................................................................3-2
Trace..............................................................................................................................................3-2
Track Voltage.................................................................................................................................3-2

TONEOHM 950 SERVICE MANUAL
x
i
i
Plane Shorts...................................................................................................................................3-2
Detailed Theory of operation..............................................................................................................3-3
Microvolt Amplifier..........................................................................................................................3-3
Trace Amplifier...............................................................................................................................3-3
Current Source...............................................................................................................................3-3
Plane Amplifier and Vector Discriminator.......................................................................................3-3
Vectored Plane Stimulus................................................................................................................3-4
Drive Source...................................................................................................................................3-5
Tone Generator..............................................................................................................................3-5
A2D2A............................................................................................................................................3-5
Power Supply. ................................................................................................................................3-5
Microprocessor...............................................................................................................................3-6
Front Panel (Schematics 1 and 2)..................................................................................................3-6
SECTION 4 – DISMANTLING INSTRUCTIONS.......................................................................................4-1
Removing the cover ...........................................................................................................................4-1
SECTION 5 – LINE VOLTAGE AND FUSE CHANGING..........................................................................5-1
LINE VOLTAGE SELECTION AND FUSE CHANGING........................................................................5-1
Changing the line voltage setting .......................................................................................................5-1
SECTION 6– FAULT DIAGNOSIS ............................................................................................................6-1
TROUBLESHOOTING HINTS...............................................................................................................6-1
SECTION 7 – MAINTENANCE AND CLEANING.....................................................................................7-1
Cleaning.............................................................................................................................................7-1
Technical Support ..............................................................................................................................7-1
Instrument repair................................................................................................................................7-1
SECTION 8 – REPLACEMENT PARTS....................................................................................................8-1
FRONT PANEL KIT ...............................................................................................................................8-2
MAIN BOARD KIT..................................................................................................................................8-3
MECHANICAL KIT.................................................................................................................................8-7
SECTION 9 – SCHEMATIC DIAGRAMS ..................................................................................................9-1

1-1
SECTION 1 PERFORMANCE CHECK
MAINTENANCE AND CALIBRATION OF INSTRUMENTS
For most of Polar Instruments’ products there are two maintenance procedures — the Performance
Check and the Calibration. Some instruments may have a single (combined) procedure.
Performance Check
The Performance Check (or Checkout Procedure) is used to verify the basic functions of the instrument.
This does not usually require the removal of instrument covers, but may require the use of external test
equipment. This procedure is not intended to verify the calibration of the instrument.
Adjustment Procedure
The Adjustment Procedure (or Calibration Procedure) is used to check and, if necessary, adjust the
instrument’s calibration settings. Before carrying out the Adjustment Procedure the instrument’s
Performance Check (if applicable) should be carried out, and any detected defects should be rectified.
The Adjustment Procedure and rectification of defects should only be carried out by qualified technician.
Recommendations for Routine Maintenance
Where a Performance Check is available for an instrument this may be used as required to confirm the
basic operation of the product.
To maintain the calibration of an instrument it is recommended that its Calibration/Adjustment Procedure
is carried out at intervals not exceeding 12 months.

TONEOHM 950 SERVICE MANUAL
1-2
PERFORMANCE CHECK
Equipment required
•DC voltage source, variable from 1V to 10V and accurate to 0.1%.
•High tolerance resistors (0.5%) of the following values: 10KΩ, 1KΩ(serial numbers
below 005975 only), 200Ω, 100Ω, 1Ωand 0.1Ω.
Procedure
•Switch on and allow the 950 to warm up for 15 minutes.
1. Plug in the Needle Probes and press 20V.
2. Apply 10V DC to the probes and check that the reading is 10V ± 4%.
3. Connect a 1KΩ0.5% and a 1Ω0.5% resistor in series.
4. Apply 10V to the series resistors. This produces 10mV across the 1ΩResistor.
5. Press 20mV and check that the reading across the 1Ωresistor is 10mV ± 4%.
6. Adjust the voltage source from 0 to 20V and check that the tone varies in pitch. A
steady warble should be generated with a negative voltage.
7. Apply 1V to the two resistors and press 2mV.
8. Check that the reading across the 1Ωresistor is 1mV ± 4%.
9. Check that varying the voltage generates varying tones. No tone should be produced
below about 50uV.
10. Press 20KΩand measure a 10KΩ0.5% resistor. The reading should be within 4%. A
warble may be generated in this range.
(a) Serial numbers below 005975:
Press 2KΩand measure a 1KΩ0.1% resistor. The reading should be within 4%.
(b) Serial numbers 005975 up:
Press 200Ωand measure a 100Ω0.1% resistor. The reading should be within 4%.
11. Press 2Ωand measure a 1Ω0.1% resistor. The reading should be within 4%.
12. Apply solder to the wire ends of a 100mΩ0.5% resistor.
13. Press 200mΩand measure the resistor by pressing the probe tips into the solder.
The reading should be within 4%. Readings vary with the pressure applied to the
probes.
14. Press TRACE and connect the Drive Source leads across a 200 Ωresistor. Turn the
DRIVE SOURCE knob fully clockwise.
15. Hold the Current Trace Probe tip near to one of the Drive Source leads and align it
for maximum response.
16. Check that the display shows 20 or more.
17. Connect the Blue and Yellow Stimulus lead together. Press PLANE twice — check
for the warning bell and that the instrument returns to Standby. Leave leads
connected.
18. Connect the Red and Green Stimulus lead together. Press PLANE once. Check for
ACTIVE LED.
19. Connect the red and black Drive Source leads across a 0.1Ωresistor. Attach the
Plane Clip to the black Drive Source lead. Probe the other end of the resistor with the
probe.

PERFORMANCE CHECK
1-3
20. Slowly turn the DRIVE SOURCE from minimum to maximum (i.e. clockwise). As the
control is rotated, check that initially all direction arrow LEDs are on, then the upper
LED only, then all LEDs are off. At the same time the tone goes from high to low then
off.
21. Reverse the connections to the Plane Probe and Clip. Rotate DRIVE SOURCE from
maximum to minimum (i.e. anti-clockwise). As the control is rotated, check initially for
no arrows or tone, then rising tone and bottom arrow on, finally all arrows on.
22. Disconnect the Red and Green Stimulus lead. PLANE should automatically ring
warning bell and return to standby. Disconnect the Plane Probe and Clip from the
0.1Ωresistor.
23. Turn DRIVE SOURCE to maximum. Select 20mV, connect the Needle Probes and
drive source leads across the 0.1ΩResistor and note reading.
24. Select 200mA. Check that reading is: (10x Reading noted above) ±10%
25. Turn DRIVE SOURCE to minimum. Check for 0 ±1mA.
26. Disconnect all cables.

2-1
SECTION 2 – ADJUSTMENT PROCEDURE
ADJUSTMENT PROCEDURE
WARNING: Hazardous voltages are exposed on the PCB when the cover is removed.
This procedure should only be performed by a technically qualified person aware of the
hazards and taking all reasonable care.
Equipment required
•High tolerance(0.1%) voltage source — 10V and 10mv.
•High tolerance(0.1%) 1Ωand 100mΩresistors.
•DVM
•Power Supply.
Before connecting to the supply:–
1. CHECK THE MAINS FUSES — see SPECIFICATIONS.
2. Connect the 950 to the appropriate line voltage and turn on.
3. CHECK the front panel lights sequence and that the 950 stops in the 20V range.
PUSH 20mV.
Display Calibration
1. Connect the Needle Probes to the 10mV source.
2. Adjust POT R196 (top RHS of Front Panel board) for a display of 10.00mV.
A2D Calibration
1. Turn the power off then hold down 2mV and PLANE — re-apply power.
2. Connect needle probes to 10mV source.
3. Observe the Active and Standby (Pass and Fail) LEDs while adjusting R163 — the
tone will decrease as the calibrated position is approached.
When ACTIVE illuminates the A2D is calibrated.
4. PUSH 2mV. The 950 will beep and enter the 20V Range.
Resistance Calibration
1. SELECT the 2Ωrange. Place the probes across the 1Ωresistor. ADJUST R713 (R30
for instruments below S/N 012213) for 1.000Ωreading ±3 Counts.

TONEOHM 950 SERVICE MANUAL
2-2
Current range adjustment
(Serial Nº. 012213 and above — below this Serial Nº. there is no adjustment.)
1. Select the 200mA range. Drive source control fully clockwise.
2. Connect the drive source and the DVM across the high tolerance 1Ωresistor.
3. Note the DVM reading.
4. Apply the needle probes across the resistor and adjust R 30 for the same reading as
the DVM ± 5 counts.
Current offset calibration — Version 8 firmware and above
1. Set the current limit to MINIMUM — switch the supply ON.
2. Select 2A on the 950.
3. Connect the power supply across the 100mΩresistor.
4. Adjust the current limit to 1.6A.
5. Using the Needle Probes measure across the 100mΩresistor CHECK for 1.44 to
1.76A on the 950 display.
(Version 8 firmware and above, main board version 5 and above.)
Select the most accurate 1.6A reading by optionally placing a jumper on one of the 4
locations adjacent to U46.
No jumper is the mid setting, H fixes slight under-reading, HH corrects large under-
reading. L fixes slight over-reading, and LL corrects large over-reading.
(Version 8 firmware, main board version 4 or below.)
Connect a 20 way integrated circuit test clip to U46
Shorting Pin 17 to Gnd corresponds to HH
14 H
13 LL
8L
No connection is nominal setting.
Once the best setting is established solder a link from the appropriate pin (if any ) to
ground.
6. Version 7 firmware and below offer no fine adjustment.
Current Trace
1. Connect Trace / Drive Source Probe.
2. Push TRACE. Adjust the volume as desired, short the drive source leads together
and turn the drive source to MAXimum.
3. While holding the probe against the Drive Source lead ADJUST R94 for the highest
displayed reading (> 500).
Move the probe away from the Drive Source leads,
4. CHECK Tone turns off and displayed reading is less than 25.

ADJUSTMENT PROCEDURE
2-3
Plane Shorts
1. CONNECT the 4 Plane Stimulus leads BLUE to YELLOW and RED to GREEN
2. Push PLANE twice to enter ACTIVE mode.
3. CONNECT the Plane Clip to the Plane Probe. Adjust R85 for a reading of 00.0 ±3
counts.
(Ser Nº 012213 up)
Adjust R716 (located near U18, behind copper shield) for minimum (or most
negative) reading.
Re-adjust R85 for 00.0 ± 3 counts.
4. Reduce the Variac to:
190V (240V instruments)
95V (120V instruments)
85V (Japanese instruments)
5. Check that PLANE remains ACTIVE
6. Remove the Green clip from the demo board and check the 950 goes to standby.
Reconnect the clip and select ACTIVE.
7. Repeat for the yellow clip.
8. Disconnect all probes.