Instruction Manual 

Fisher Scientific Isotemp

Standard Ovens 

600 Series 

 Model 625 (Small) 

 Cat. No. 13-247-625G & -626G 

 Model 637 (Medium) 

 Cat. No. 13-247-637G & -638G 

 Model 650 (Large) 

 Cat. No. 13-247-650G & -651G 
Table of 

Contents 

Introduction..............................................................................1 

Installation

 Selecting a Location ........................................................2 

 Unpacking........................................................................2 

 Preparing the Oven..........................................................3 

 Power Switch...................................................................3 

Controls.....................................................................................4 

Operation..................................................................................5 

Safety Precautions ...................................................................5 

Limit Alarms............................................................................6 

Calibration................................................................................7 

Service .......................................................................................9 

 Replacing the Door Gasket............................................10 

 Replacing and Adjusting the Door Handles..................11 

 Replacing the Door Hinges ...........................................12 

 Accessing the Electronics Compartment.......................13 

 Replacing the Heater .....................................................15 

 Replacing the Controller ...............................................16 

 Replacing the Control Thermocouple ...........................17 

Troubleshooting .....................................................................18 

Replacement Parts.................................................................19 

Performance Characteristics................................................20 

Specifications..........................................................................21 

Electrical Schematic ..............................................................22 
Page 1 Isotemp Standard Ovens 

Introduction Fisher Isotemp 600 Series Standard ovens are available in three sizes: 

small (Model 625), Medium (Model 637) and Large (Model 650). All 

models provide analog, on/off control at operating temperatures ranging 

from 50 o

C (122 oF) to 225oC (437 oF). 

Inlet air enters through a port located under the oven floor. Heatgenerated convection then gently moves the air in a vertical circulation 

pattern. Exhaust air is vented through a port at the oven top. 

 The Model 625 accommodates a maximum of five shelves. The Model 

637 holds eight shelves, while the 650 holds up to eleven shelves. 

 Isotemp ovens incorporate a variety of safety features. A safety backup is 

built into the controller: if the primary heater control fails, the backup will 

maintain control at 5 o

C above the set point. An alarm LED then indicates 

that the backup controller is operating the oven. A circuit breaker protects 

the oven from power surges. 
Isotemp Standard Ovens Page 2 

Installation 

Selecting A Choose a location for the oven which will provide an area approximately 

Location 2 ft. x 2 ft. The bench or table selected must be capable of supporting at 

 least 120 lbs for the Models 625, 130 lbs for the Models 637 or 135 lbs 

for the Models 650. Appropriate electrical power must be available. 

Locate the oven within three feet of the power outlet so that no extension 

cord is required. 

Unpacking Fisher Isotemp ovens are shipped in a single carton. After unpacking, 

locate each item shown in the list below. Report any missing items, by 

name and part number, to your Fisher branch. In the event of shipping 

damage, retain the shipping material and file a claim with the final 

carrier. 

Item 

Oven Assembly

 Model 625 (small) 

 120 V, 50/60 Hz 

 240 V, 50/60 Hz 

 Model 637 (medium) 

 120 V, 60/50 Hz 

 240 V, 50/60 Hz 

 Model 650 (large) 

 120 V, 60/50 Hz 

 240 V, 50/60 Hz 

 Shelves

 Models 625 & 637 (two provided); one fixed, one moveable 

 Model 650 (two provided); one fixed, one moveable 

 Shelf Supports

 Models 625 & 637 (four provided) 

 Model 650 (four provided) 

 Instruction Manual

 
Page 3 Isotemp Standard Ovens 

Preparing the To prepare the oven for operation, perform the following procedures: 

Oven

1. Install the shelf. 

 2. Make certain all packing material has been removed from oven 

 chamber. 

 

 3. Connect the line cord to an appropriate electrical outlet. 

 

Caution: See data plate on oven for voltage, current and line 

 frequency specifications. Check that the power 

 requirements of the oven will not overload the circuit 

 

4. The oven is now ready for operation. No preliminary adjustments are 

required. 

Note: The oven received a single point calibration at 120° C +/- 2°C at the 

factory. If greater accuracy is required the user may require a standard 

laboratory calibration. (See page 7.) 

Power The 600 Series ovens feature a front panel mounted power switch which 

Switch is a combination power switch and circuit breaker, eliminating the need 

for separate fusing. The circuit breaker will interrupt power in the event 

 of an oven heater malfunction. 

 

 Press the I (upper) half of the rocker-type power 

 switch to the in position to turn the oven on. Press the 

 0 (lower) half to the in position to turn off oven 

 power. To reset the breaker, first place the switch to 

 the off position, then return it to the on position. 

Off

O 

I 

On
Isotemp Standard Ovens Page 4 

Controls The 600 Series controller features three LEDís which indicate, 

respectively, that power is being applied to the oven heaters, an alarm 

condition exists or that oven power is on. A temperature dial, marked in 

ten degree increments, serves to set the oven temperature. 

 Front Panel 

 

Temperature Sets the oven operating temperature in degrees 

Dial Celsius (oC). 

 

 Heat Indicator Lights when power is being supplied to the oven 

 heater. 

Alarm Indicator Lights if the actual oven temperature exceeds the 

 alarm temperature. The alarm temperature is 

 factory-adjusted to be 5 o

C above the set 

 temperature. 

Power Indicator Lights when power is on. 
Page 5 Isotemp Standard Ovens 

Operation The 600 Series ovens maintain a set temperature until that set temperature 

 is changed. 

 To achieve a set temperature, simply perform the following: 

1. Rotate the temperature dial full counter-clockwise. 

2. Place the power switch in the ON position. The Power indicator will 

come on. 

3. Rotate the temperature dial to the desired set temperature. The Heat 

indicator will then come on. 

4. When the actual temperature approaches the set temperature, the Heat 

indicator will cycle on and off, maintaining the set temperature.

 1. After controlling at a given temperature, if the 

 temperature dial is rotated CCW, the alarm indicator 

 will come on. This is normal operation. 

Note: 

 2. Since this is an analog control with 10 degree 

 increments, the user may choose to add a 

 thermometer and make minor adjustments to reach a 

 more precise temperature setting. 

Safety 

Precautions 

Before operating the oven, always observe the following Safety 

Precautions: 

This unit is not explosion proof, do not use in the presence of 

flammable or combustible materials; fire or explosion may result. 

Unit contains components, which may ignite such materials. 

Fumes and spillage from acidic solutions cause corrosion of the 

stainless chamber. Care should be taken to maintain a neutral pH at 

all times.

• Wear insulated gloves. 

• Use tongs. 

• Never stand in front of an open oven. 

• Use safety goggles. 

Caution: Removal of safety shield, shelf support, and/or shelf will 

 result in voiding of warranty. Heater cover is not a suitable 

 replacement for a shelf and must not be used as such. Use of 

 heater cover as a shelf may result in fire. 
Isotemp Standard Ovens Page 6 

Limit The 600 Series controllers feature a deviation alarm which alerts the 

Alarms operator and interrupts heater power whenever the actual oven temperature 

 differs from the set temperature by more than 5 o

C. This set limit cannot 

 be adjusted by the operator. 

 If the actual temperature exceeds the alarm limit, the alarm indicator LED 

 will light. 

 The reference point for the alarm is the set temperature. Any change in the 

 set temperature will cause a corresponding shift in the alarm temperature. 

Example:

 If the set temperature is 150 o

C, the alarm will trip at 155 oC. If the set 

 temperature is changed to 200 oC, the alarm will follow the set 

 temperature and trip at 205 o

C. 

 Changing the set temperature to a value more than 5 o

C below the present 

 oven temperature will trip the alarm. Power is removed from the heater 

 when an alarm condition occurs. 
Page 7 Isotemp Standard Ovens 

Calibration The 600 Series controllers are factory calibrated near the center of the 

oven's operating range and will usually remain reasonably accurate over a 

long period of usage. However, should the accuracy diminish with time, or 

should the user require greater accuracy at a particular temperature setting, 

the controller may be recalibrated. 

The temperature controller has high and low temperature range 

adjustments located under the skirt of the set temperature dial. 

 To recalibrate the controller, perform the following procedures: 

1. Place a calibrated thermometer (preferably traceable to NIST standards) 

in oven chamber. 

2. Rotate temperature dial full counter-clockwise (CCW). 

3. The dial line should point to 20 °C. If not, loosen the setscrew holding the 

dial on its shaft. Rotate shaft until dial line points to 20 o

C, then re-tighten 

set screws. 

4. Press oven Power switch to ON (1) position. 

5. Rotate temperature dial to 40 °C. Heat indicator will come on full, then 

begin to cycle on/off as the oven approaches final temperature. 

6. After the Heat indicator begins cycling, allow an additional 30 minutes 

for the oven to achieve a final, stable temperature. 
Isotemp Standard Ovens Page 8 

7 Carefully remove the temperature dial knob without rotating it. 

8. Use a thin blade screwdriver to calibrate Low Adjust. Check thermometer 

reading. If reading is less than 35 oC, rotate Low Adjust CCW slightly to 

turn heater on. If reading is above 45 oC, rotate Low Adjust CW slightly 

to turn heater off at lower temperature. After each adjustment allow 

sufficient time for oven temperature to re-stabilize. Repeat until 

thermometer reading is 40 oC ± 5 oC 

9. Replace temperature dial knob with pointer at 40 oC, then tighten 

setscrew, being careful not to rotate the dial shaft 

10. Set temperature dial to 200 oC. 

11. After the Heat indicator begins cycling on/off, allow an additional 30 

minutes for oven to reach a final, stable temperature. If thermometer 

reads 200 ± 5 o

C, calibration is complete. Otherwise, continue with 

following steps. 

12. Carefully remove the temperature dial knob without rotating it. 

13. Use a thin blade screwdriver to calibrate High Adjust Check thermometer reading. If reading is less than 195 o

C, rotate High Adjust CW 

slightly to turn heater on. If reading is above 205 o

C, rotate High Adjust 

CCW slightly to turn heater off at lower temperature. After each 

adjustment, allow sufficient time for oven temperature to re-stabilize. 

Repeat until thermometer reading is 200 ± 5 oC.

14. Replace temperature dial knob with pointer at 200 oC, then tighten 

setscrew, again being careful not to rotate the dial shaft 

15. Set the temperature dial to 180 oC. The Alarm indicator should come on 

if calibration is correct. 
Page 9 Isotemp Standard Ovens 

Service The following sections describe procedures for servicing the 600 Series 

ovens. Most users may perform the first procedure, replacing the Door 

Gasket. However. All other service procedures involve potential exposure 

to line voltage. Only qualified service personnel should undertake these 

procedures. The second section, Accessing the Electronics Compartment, 

describes procedures required for subsequent service sections and is 

referenced by these later sections when required. 

 

 Service procedures involve exposure to line voltage 

Caution: and should be done only by qualified service 

 personnel. Disconnect oven from power source 

 before attempting repairs. 

For Technical Assistance call: 1 (800) 926-0505 

 For Field Service Division Assistance call: 1 (800) 395-5442 
Isotemp Standard Ovens Page 10 

Replacing the Isotemp 600 Series ovens incorporate a durable, silicone door gasket to 

Door Gasket minimizes heat loss. Should the gasket become defective or be damaged, it 

may be replaced by following the procedure below. 

1. Set the power switch to off position and open chamber door. 

Caution: 

Allow oven to cool to ambient temperature before 

 attempting repair. 

2. Open door fully and lift it off of hinge pins. Lay door on a flat surface 

with the handle over the edge. 

3. Note the joint position of the old gasket. This is where the new gasket 

installation will start. 

 Study the method of door gasket attachment before 

Note: starting disassembly. This understanding will avoid 

confusion later in this process. 

4. Bend back the old door gasket and remove the Phillips head 

screws attaching the gasket. 

5. Remove the old door gasket. 

6. Loosely install two screws through the stainless steel liner and 

into the door wrap to align these pieces. 

7. Begin installing the replacement gasket at the joint position of the 

old gasket. Stretch the replacement gasket around the corners of 

the liner to avoid bunching up of the gasket material. 

8. Install a Phillips head screw as the gasket rounds each corner to 

keep the gasket properly stretched. (The screw goes through the 

liner, pierces the gasket and threads into the door wrap.) 

9. After all four corners are secured install the remainder of the 

Phillips head screws. Make sure there is no gap at the gasket joint; 

stretch the gasket slightly if necessary. 

10. Reinstall the door onto the hinge pins. 
Page 11 Isotemp Standard Ovens 

Replacing To replace a defective door handle, perform the steps below: 

the Door 

Handle 1. Remove the two mounting screws holding latch cover in place. 

1. Remove the two mounting screws holding defective handle in place. 

2. Mount the replacement handle. 

3. Adjust bottom of cam .88 from end of shaft. 

4. Secure latch cove in place with 2 screws. 

Adjusting the Due to handling in shipment or to heat distortion with use, the door cam 

Door Cam may require adjustment. To facilitate proper closing and sealing of door, 

 Steps 1 through 5 may have to be performed concurrently. 

Caution: 

 Allow oven to cool to ambient temperature before 

 attempting repair. 

To adjust the door cam, perform the following: 

1. Open door and remove screws holding latch cover in place. 

2. Locate nuts securing tongue on camshaft. 

3. Loosen, but do not remove outside nut.

4. Adjust inside nut (one full-turn counter-clockwise draws door 1/16 inch

closer to cabinet when door is closed.

5. Secure cam tongue in place by tightening outside nut.

6. Secure latch cover in place with 2 screws.
Isotemp Standard Ovens Page 12 

 

Replacing To replace a defective door hinge, perform the steps below: 

the Door 

Hinges 

1. Loosen hinge Screws, one from each hinge. Remove chamber door 

Caution: 

 Allow oven to cool to ambient temperature before 

 attempting repair. 

 

 2. Remove the two mounting screws securing the defective hinge. 

 3. Remove defective hinge and mount new hinge by replacing the 

mounting screws. 

 4. Put door back onto hinges. 

 5. Tighten hinge set screws. 
Page 13 Isotemp Standard Ovens 

Accessing the To access the electronics compartment, proceed as follows: 

Electronics 

Compartment 

5. Disconnect power cord from the electrical outlet. 

Caution: 

 Allow oven to cool to ambient temperature before 

 attempting repair. 

 

 2. Open the chamber door. Carefully lift the oven door upward and off its 

two hinges. Set door aside. 

 Caution: Service procedures requiring access to the 

 electronics compartment involve exposure to line 

 voltage and should be done by qualified service 

 personnel. Disconnect incubator from power before 

 attempting repairs. 

 

3. Slide the oven back until the front of the bezel (control panel) is at 

least three inches from the edge of the bench top. 

4. Prop up the oven front by placing a shim under each front foot. 

Use shims between one and one-half and two inches in thickness. 

5. Remove two screws securing bezel from bottom of oven. 
Isotemp Standard Ovens Page 14 

 

6. Grasp bezel and pull bottom outward. Bezel will disengage from 

fascia. Lay bezel on benchtop in front of oven. 

 Service procedures requiring access to the 

Caution: electronics compartment involve exposure to 

 line voltage and should be done by qualified 

 service personnel. Disconnect incubator from 

 power before attempting repairs. 
Page 15 Isotemp Standard Ovens 

Replacing To replace a defective heater, proceed as follows: 

the Heater 

1. Disconnect power cord from the electrical outlet 

Caution: Allow oven to cool to ambient temperature before 

 attempting repair. 

2. Remove two screws that secure oven safety shield and heater 

cover. Remove screws securing shelf supports on each side. 

3. Remove the heater cover by lifting and sliding it forward. It may 

be necessary to use a flat-blade screwdriver to assist in lifting the 

cover upward. Set heater cover aside. 

4. Remove the two nuts and shake proof washers securing the heater 

leads, then pull the lead terminals off the heater studs. 

5. Remove the two screws securing heater to cabinet. Slide heater 

for-ward to disengage back heater clips, lift back of heater up, 

then slide heater back and lift out. 

6. Install replacement heater and re-assemble oven by generally 

reversing the steps above. 

Caution: Service procedures requiring access to the electronics

 compartment involve exposure to line voltage and should

 be done by qualified service personnel. Disconnect 

 oven from power before attempting repairs.
Isotemp Standard Ovens Page 16 

Replacing To replace a defective controller, proceed as follows: 

 the 

Controller 

1. Complete the procedures discussed in Accessing the Electronics 

Compartment. 

2. Remove temperature dial knob. 

3. Locate three push-on terminals at right hand side of controller board 

(heater wire, two power wires). Disconnect the three lead wires by 

pulling up and off terminals. Note connections for later re-assembly. 

4. Remove four screws, which mount the controller board to the bezel. 

Lift out board. 

5. Loosen set screws in two-position terminal at front of controller board 

and disconnect thermocouple wires. Thermocouples are polarity 

sensitive so make a note of which terminal is red and which is yellow 

for reassembly. 

6. Install replacement controller by generally reversing the steps above. 

When replacing the temperature dial, first rotate the 

Note: dial shaft full counter-clockwise. Then replace knob 

 with pointer at the 20 degree mark. 

Caution: Service procedures requiring access to the 

electronics compartment involve exposure to line 

voltage and should be done by qualified service 

personnel. Disconnect oven from power before 

attempting repairs. 
Page 17 Isotemp Standard Ovens 

Replacing To replace a defective control thermocouple, proceed as follows: 

the Control 

Thermocouple 1. Complete the procedures discussed in Accessing the Electronics 

 Compartment. 

 2. Remove thermocouple wires from 2-terminal connector by loosening two 

securing screws. 

 Observe position in terminal for each lead. 

Note: when re-connecting, be certain to observe 

 polarity. Compare with polarity indication on 

 controller housing. For thermocouples, the red 

 wire is negative and yellow positive. 

3. Loosen 2 screws at lower front of oven chamber that secure the safety 

shield. Lift shield upward to free bottom shelf. Pull bottom shelf outward 

to access the thermocouple. 

 4. On back wall of oven, locate the two clips, which hold thermocouple in 

place. Remove thermocouple from clips. 

 5. Pull thermocouple forward and out through side hole in oven chamber. 

 6. Carefully feed leads of replacement thermocouple through side hole in 

oven chamber and oven insulation. 

 7. Reaching into electronics compartment, pull thermocouple leads into place. 

 8. Generally reverse steps 1 through 3 to complete installation of new 

thermocouple and reassemble oven. 

 9. Align thermocouple correctly in clips near back wall of oven. The end of 

the thermocouple should protrude only 1/4 " over the left side of the oblong 

hole in the heater cover. This will give the best control. If during the 

calibration steps, you run out of adjustment on the HI range potentiometer, 

set the sensor so only 1/8" is over the oblong hole. 

 

 10. Slide lower shelf back and reinstall the safety shield. Fasten shield under 

screws that attach the heater cover. 

Caution: Service procedures requiring access to the 

 electronics compartment involve exposure to 

 line voltage and should be done by qualified 

 service personnel. Disconnect oven from 

 power before attempting repairs. 
Isotemp Standard Ovens Page 18 

Trouble- This table is intended to assist in resolving oven problems by relating 

Shooting symptoms to their likely cause. The service discussed below is beyond 

Table the scope of most users and should be performed by qualified and trained 

 personnel. 

Symptom Probable Cause Action 

No power Unit not plugged in or turned on. Plug in or turn on. 

 

 Defective circuit breaker. Replace circuit breaker. 

Oven temperature Defective control thermocouple Replace control thermocouple 

erratically high 

Failure to heat Set temperature less than Refer to Operation

 Actual temperature 

 Defective control thermocouple Replace control thermocouple 

 Poor heater connections Tighten connections at terminal 

strip 

 and/or heater. 

 

 Defective heater element Check heater resistance on 

 Schematic at back of manual. 

 Replace heater unless 

approximately the same as 

schematic. 

 Defective controller Replace controller 

Alarm LED stays on and Set temperature has been Wait for actual temperature to cool 

control is higher than set changed to a value less than to the set temperature. 

temperature the actual temperature minus 

 the alarm limit 

 Defective controller Replace controller 
Page 19 Isotemp Standard Ovens 

Replacement Replacements for oven parts may be ordered, by part number, from

Parts Fisher. 

Item Part Number (ref) 

 Line Cord and Plug 

 Models 625, 637, 650 (120V) SPN 56636 (LINE) 

 Models 625, 637, 650 (240 V) SPN 95706 

 Temperature Controller 

 120 V SPN 95911 (CTRL) 

 240 V SPN 95912 

 Thermocouple Assembly SPN 95603 (TC) 

 

 Handle SPN 104976 

 Shelf (Fits All Models) 13-247S 

 Shelf Support (Need two per shelf) SPN 95635 

 Heater Assembly 

 Model 625 (120 V) SPN 95695 (HTR) 

 Model 625 (240 V) SPN 95736 

 Model 637, 650 (120 V) SPN 95695 

 Model 637, 650 (240 V) SPN 95736 

 Door Gasket 

 Model 625 SPN 101908 

 Model 637 SPN 101909 

 Model 650 SPN 101910 

 

 Circuit Breaker 

 Single Pole (120 V) SPN 95765 (S1) 

 Double Pole (240 V) SPN 95786 
Isotemp Standard Ovens Page 20 

Performance 

Characteristics

 Operating Range 50 to 225 o

C 

 Average Uniformity @ 200 o

C ± 4.5 oC 

 Resolution 1 oC 

 

 Control Sensitivity ± 0.5 oC 

 Recovery time @ 200 o

C (door opened 

 one minute) 

 

 Model 625 2.0 minutes 

 Model 637 4.0 minutes 

 Model 650 4.0 minutes 

 Rise Time to 225 o

C 

 

 Model 625 45 minutes 

 Model 637 60 minutes 

 Model 650 120 minutes 

 Air Exchanges 

 Model 625 24 per hour 

 Model 637 16 per hour 

 Model 650 12 per hour 

 BTU/hour Output @ 100 o

C @ 200 oC 

 Model 625 470 1325 

 Model 637 1040 2025 

 Model 650 1150 2040 
Page 21 Isotemp Standard Ovens 

Specifications 

Electrical Requirements 

Model 625 

 Cat. No. 13-247-625G 120 V, 50/60 Hz 

 Cat. No. 13-247-626G 240 V, 50/60 Hz 

 Model 637 

 Cat. No. 13-247-637G 120 V, 50/60 Hz 

 Cat. No. 13-247-638G 240 V, 50/60 Hz 

 Model 650 

 

 Cat. No. 13-247-650G 120 V, 50/60 Hz 

 Cat. No. 13-247-651G 240 V, 50/60 Hz 

Power Requirements 

 Model 625 1300 W 

 

 Model 637 1300 W 

 Model 650 1300 W 

Chamber Volumes

 Model 625 2.5 cu ft. 

 Model 637 3.8 cu ft. 

 Model 650 5.0 cu ft. 

Chamber Dimensions (W x D x H)

 Model 625 18 x 18 x 13.5 in 

 Model 637 18 x 18 x 20 in 

 Model 650 18 x 18 x 26.5 in 
Page 22 Isotemp Standard Ovens 

Electrical Schematic 
Fisher Scientific Phone Numbers:

 Fisher Technical Assistance: 1-800-926-0505 

 Fisher Service Division Assistance: 1-800-395-5442 

 Fisher Sales Support: 1-800-766-7000 

Part No. 95583 Rev. H 

600 Series Standard Ovens 

Published 04-2003