Buttfuzz' Repair Tips & Tricks...

PROBLEM: Excessive arcing of the high voltage contacts of the relay.
CURE: Remove CD601 (1N4005 diode), presently connected with its cathode to the junction of R317 and R319 and its anode to ground.  Reconnect the cathode to the junction of R316 (1.5K labeled R327 on the board), and the orange and pink wires that go to the mode switch and relay.  Connect the anode to ground.  This will shunt to ground a negative pulse that can exceed the voltage rating of the contact.

PROBLEM: Radio has no transmit or receive. Sometimes only transmit cuts out. Loss of normal operation.
CURE: Locate C54. This is a 1f 20 volt tantalum capacitor located near the main PLL chip. Replace with a 1uf 35 volt tantalum capacitor. This should restore normal operation in most cases. Some slight tweaking of the VCO coil may be necessary for complete coverage of all 40 channels. If you experience any further problems with the unit try replacing this tantalum with a non-polarized one of the same value.

MODEL: Cobra 29 (old, CS)
PROBLEM: LOW Modulation
CURE: 1. Change R98 to 2.7K
2. Change R99 to 3.3K
3. Change R60 to 470 ohms
4. Delete C97
5. Change C135to 0.0047mfd
6. Change C57 to 0.0022mfd
7. Reverse L8
8. Install a heat sink on driver transistor TR19

MODEL: Cobra 62XLR
PROBLEM: No Squelch
REMEDY: Cut the foil pattern between the base of the TR-8 and the junction of D-12, C-17.  Add a 1K, 1/4 watt resistor in series with the base circuit of TR-8.

MODELS: Cobra 142GTL, Cobra140GTL, Cobra 2000GTL, 148GTL,
Washington, McKinley, Grant, Madison (New Models)
PROBLEM: TR34 (2SC1419 AM Regulator failure.) TR41 in 2000 GTL, 148GTL, Grant & Madison.
2SC1419 not capable of handling FULL POWER OUTPUT, Radio transmits on SSB but not on AM!
REMEDY : Change 2SC1419 (2 amp) to a GE-66 (10 amp) or NTE-152 (7 amp)

MODELS: Cobra 142GTL, Cobra 140GTL, Cobra 148GTL
PROBLEM: High Power AM output (10 watts) and no modulation; weak or no receive
CURE: Replace IC5 (IC4 for 148 GTL) and change D60 to (D44 for 148GTL) to an 18.2 volt zener diode. Add a SRlk2 diode from pin 1 to pin 2 of IC5 (IC4 for 148 GTL). (Use Diode from D-60/44) DynaScan Part numbers SR1k2 151-045-9-001 Sub 16.2 Volt Zener 152-057-9-001. 18.2 Volt Zener (P/N N.A. as yet) to be used when in stock.

MODEL: Cobra 139XLR
PROBLEM: After radio has been on for a period of time, high temperature generated by TR-36 and R-153 overheats the SSB crystals thereby causing excessive transmitter or receiver drift on SSB operation.
CURE:  Keep it cool, fool. See also cobra downloads on this site...

MODELS: Cobra 139XLR, Washington (858 Chip), Madison (858 Chip), ROBYN 520D & 510D.
PROBLEM: Relay Buzzing on SSB transmit, causes lights to dim, sometimes fuse will blow. Usually no AM transmit, too.
REMEDY : Locate C-179 in the Final Output circuit. This is a 2.2 of ( 25 Volt) small blue Tantalum Electrolytic. Change this component to a standard 2.2 of (50 Volt) Electrolytic Capacitor. This should restore proper operation on most units.

MODEL: Cobra 142GTL
PROBLEM: A/C Hum in audio.  Most noticeable through headphones or when volume is low.
CURE: Unsolder black ground wire (FROM cable harness) at power supply board. Remove small tie wrap which wraps red & Black wires together. Pass black ground lead through large chassis hole and re-solder directly to negative terminal of filter capacitor C-304 on bottom of power supply board. Negative terminal faces front of unit.

MODELS: Cobra 2000GTL, 148GTL
PROBLEM: Popping/Cracking when mod limiter (TR-24) removed.
CURE: Remove C-232 electrolytic capacitor.

MODEL: Cobra 2000 GTL
PROBLEM: Frequency Counter unstable. Reading very erratic.
REMEDY : Cure: Locate D528 (XZ057) in frequency counter module. This is a 5.7 volt 1/2 watt zener
diode. Replace with an NTE-136A 1 watt.

PROBLEM: Digits continue to glow very dimly after radio is turned off. Frequency counter may be unstable also.
REMEDY: Replace Fet-501 & Fet-502 located in Frequency Counter Module. This should restore normal operation. Be sure use only an isolated soldering unit when replacing these FET's or doing any soldering in the frequency counter module.
NOTE: Older versions of the cobra 2000 used 25k19GR as the part number for Fet-501 and FET-502. Newer versions use 25k192A.

Radio : Cobra 2000GTL
Problem: Radio has no audio on AM transmit, but has a good dead key carrier. Radio has no SSB transmit. However it has good receive audio on AM and SSB. This problem seems to be appearing quite frequently in some of the older 2000GTL units.
Cure: Check the collector of TR23 (Mic Amp) for about 4.5V while you key the radio on AM. If this voltage is absent or low check for 6.5V on the other side of R120. One side of R120 connects to the collector of TR23, and the other side connects to the supply voltage from the power supply. If this voltage is absent then C18 has shorted and will need to be replaced. C18 is a 330pF 10V electrolytic located just to the right of L31. When replacing C18 use a 16V replacement in order to prevent any future problems from occurring.

Radio: Colt Excalibur 1200
Problem: Lights Dimming on TX, Poor Performance
CURE: Replace small wires from PCB to Power supply with 18 ga wire, and shorten to only length needed.

CURE: AT FACTORY, drivers are torqued down too tight. Replace driver and nut insulator.

PROBLEM: Unit lights up but has no digital channel display. No receive or transmit.
CURE: Locate D2 -- a MZ205 5.2 volt zener diode just to the right of the main PLL chip. Check for 5.2 volts on the cathode (banded) side. Normally if this voltage is absent, just replacing this zener will restore normal operation. If after replacing D2, the unit still does not function properly you will need to check Q44 for the correct voltages.

The base of Q44 should read about 9.5 Volts, the collector should read about 13.2 Volts and the emitter should read about 8.9 volts. If you have the 13.2 Volts on the collector but do not have 8.9 volts on the emitter, replace Q44 (2SC 1173)
with a NTE-152 and D50 (located next to Q44). D50 -- is a MZ310 (9.1 zener diode). Replace this with an NTE-139A. This should restore normal operation.

MODELS: GALAXY SATURN (And export models using same Freq. Counter Module)
PROBLEM: Frequency Counter Problems.
The common problem with the GALAXY SATURN frequency counter is after it is on a while the read-out becomes unstable. Sometimes the display
will quit all together. Turning off the unit and allowing it to cool for a short period of time will usually restore correct operation.
This problem has been traced to a Zener Diode inside the frequency counter module. It is marked D-603. This is a 2.4 volt, 1/4 watt zener
next to IC-609 (LM-7808) regulator.
REMEDY: Change D-603 to a NTE-5000A (2.4 volt, 1/2 Watt ) zener. This should restore normal operation.

MODEL: GALAXY SATURN (Also other export models using similar CHASSIS BOARD.)
PROBLEM: Distortion on SSB sometimes causing failure of TR-51 (2SB-754 ).
REMEDY : This problem is usually caused by having the SSB ALC adjustment turned up too high.
Do not adjust VR-12 full open (11 o'clock position). Normally this adjustment should be not be turned past the 6 o'clock position.

PROBLEM: Loss of transmit. Bad TR-51 (2SB-754).
CURE : This is a very common problem in this radio. The 2SB-754 seems to be some what under-rated for this circuit. Replace 2SB-754 (7 Amp, 60 Watt) with an NTE-37 (12 Amp, 100 Watt). This should not only return the unit to normal operation but also help to prevent any future problems.

Problem: Transmit power is very low (1 to 3 watts on AM). The Transmit Driver and Transmit Finals all test good. No amount of adjustment will improve the power level. Power is also low on SSB as well. TR44 driver bias (VR11) will not adjust.
Cure : This problem is usually caused by a defective Driver Bias Adjustment (VR11 1K Variable Driver Bias Adjust). Usually when VR11 starts to fail, the above symptoms tend to happen gradually, causing intermittent low power levels on transmit. Eventually VR11 will fail completely and the above symptoms will be constant. Normally replacing VR11 will cure the problem. Once VR11 has been replaced, be sure to readjust the bias levels on the transmit Driver and Final.

MODEL: MB8719 Chassis with AMC transistor pulled. (TR-32)
PROBLEM: DISTORTION/ All Sorts of Noises in TX.  Intermittent and not in all units.
CURE: REMOVE TR-33 (AMC Sensor Transistor)

PROBLEM: Unit lights up, has sound from speaker, but no channel display. Loss of normal operation.
CURE: Locate the M7805 regulator on the main PLL board. Check for 5 Volts on the #3 leg of this component. If you find this voltage is absent, you will need to replace the M7805 regulator. A direct replacement part number for the M7805 regulator is NTE 960. Next replace the sub-miniature 1000uf 6.3 Volt electrolytic directly behind the 64 pin chip with a sub-miniature 1000uf 10 Volt capacitor. This capacitor normally becomes shorted in most all the units, thus causing the 7805 regulator to fail in most cases... Changing this electrolytic from a 1000f 6.3 Volt to a 1000f 10 Volt will help to eliminate any future problems.

PROBLEM: Squeal on transmit.
REMEDY : Locate audio lead on the mike socket.
Place two RF Beads on this line.
Run a .001 uf capacitor from the audio pin to ground.

Noisy receiver. Unit has a high level of vehicle noise (i.e., Fan noise, Fuel Pump noise, etc.)
REMEDY: To reduce front end overloading on the RCI-2950 (i.e., quiet the receiver) change R78 from a 2.2K resistor to a 10K resistor. This modification will reduce the bias on the first RF Amplifier, Q18, thus aiding in reducing impulse noise created by the various electronic or electric components in the installed vehicle. In some of the more difficult cases, a .047uf electrolytic capacitor may need to be installed across the power terminals of electronic fuel pump or fan motor. Additional filtering may be also required across the radio's DC input. Any good commercial filter rated at least 15 Amps or higher can be used.

 Stations close by sound distorted or garbled. However distant stations sound O.K. Automatic Gain   Control does not seem to be functioning properly.
To reduce the effects of A.G.C. overload on receive; change R49 from a 100K resistor to a 33K resistor. Normally this will cure the problem in most units. In some units it will also be necessary to change R78 from a 2.2K resistor to a 10K resistor in order control front end overloading of the receiver.

Unit fails to operate on initial turn on. Turning the radio off then back on causes the radio to operate.
REMEDY: This problem is usually caused by the V.C.O. being out of lock. In order to prevent future occurrences, it will be necessary to change C107 to a 100pf NPO disk capacitor. Once this capacitor has been replaced you will need to readjust the V.C.O. voltage.  Locate J13 and connect a DC volt meter between it and ground. Set the radio to 28.0 MHz and then adjust L17 for a 1.9 volt reading on the DC volt meter.

 The Variable Frequency Adjust located above the microphone jack does not operate properly. Several clicks are required before the frequency changes.
REMEDY: A resistor change will be required in order to cure this problem. Locate and change R611 on the microprocessor board from a   47K Ohm chip resistor to a 10K Ohm chip resistor.  If a 10K Ohm chip resistor is not available a standard 1/8th watt 10K resistor can be used.

 Premature battery failure.
REMEDY: The lithium memory battery which is installed on the microprocessor should have a normal lifetime of 2  to  3  years under normal use. One cause for premature failure of this battery is the excessive use of the reset switch (S601). This switch can be used to disrupt the normal power up and power down initialization process that the microprocessor executes. One alternative is to advise the customer of this problem and to avoid excessive use of the reset switch. The best solution is to remove S601.

PROBLEM: Low Power and/or reverse modulation when expanding the frequencies.
CURE: Replace C4 (68pf) with 100pf, replace C22 (2pf) with 5pf.

 Battery Replacement Procedure for RCI-2950
REMEDY: Remove the defective battery , and replace. After the new battery has been installed it will be necessary to re-initialize the microprocessor for proper operation. To do this turn the unit on and then back off again. Once this has been done turn the unit back on and check for proper operation. If all functions seem to be operating then turn the unit off and allow it to set for about 5 minutes or so. After the unit has set for this period of time, check the voltage of the new battery in order to make sure there are no shorts which are causing the battery to fail. If the voltage begins to drop, the microprocessor may be defective and will need to be replaced.

PROBLEM: Erratic or no power switch operation
CURE: Power switch on early production runs is marginal and will build up carbon. Replace with R/S PN RRVY271001, on/off-vol, or equivalent.

PROBLEM: Transmit and receive come and go. Sometimes receive will stay in but transmit does not function at all times. Radio acts as if it has a loose connection.
REMEDY: Locate C524 just to the left of IC501 PLL chip. This is a small orange luF 20V tantalum capacitor. Remove and replace C524 with a new 1uF 35V tantalum capacitor. Some adjustment of the VCO may be necessary if the unit does not lock in and function on channel 1 and channel 40.

CURE: Engineering investigation of the Sidebander II/Console II has determined that the removal of diode D7 will improve cross modulation rejection approximately 10db. It is recommended that any units returned for warranty or non-warranty service have diode D7 removed. No alignment or adjustment is necessary once diode D7 is removed. This change has been incorporated in all Sidebander II's / Console II's shipped from the factory after April 26, 1976.

MODEL : All Radios
PROBLEM: Overmodulation
REMEDY : Overmodulation sometimes occurs after cutting or removing a diode or capacitor from circuit. If you find you are having this problem or the customer complains of distortion on transmit, this will provide you with information on how to effect a cure without cutting back on performance. All that is required is to simply insert a resistor (1k to 15k value) in series with either the diode or capacitor that you cut or removed from circuit. Of course if you did remove anything completely from the circuit, it will be necessary to replace the original part first. Then you may proceed from there. Experimentation will be required until you find the correct resistor value.

MODELS: upd858 Chassis
PROBLEM: Blows fuse when keyed - final transistor is good.
CURE: Change C179 (2.2Mfd/25v tantalum to higher voltage/same value.

MODELS: upd858 SSB Chassis
PROBLEM: Warble on 'upper' channels, OK for normal channels.