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Repairing a Tektronix 2445B ... (ARG)

 

Hi, I m from Argentina. I m repairing a 2445B. When I turn on it, the panel control lamps flashing one time only. The TRC never drawing anything.
I check the J119 voltages, for example....pin # 1. (-15V) I read -14,6V (+/- 0.2V) pin #8 I read 82V (+/- 0.3V) etc etc etc. The readouts are nearby but are not exactly.

Any suggestions?

Thanks.-
 

Power supply voltages are very important. I would recommend disassembly of scope and remove PS as a unit. Pay very close attention to the wiring connections. Then separate the inverter and regulator boards. Start replacing the electrolytic capacitors. C1220,C1240,C1260,C1280,C1300,C1330,C1350 on the regulator board.
Then C1111,C1110,C1102,C1101, C1113,C1116,C1114,C1115,C1132,,C1120,C1130, C1072,C1066.on the inverter board.
You will definitely need service manual to ID these parts. Match the cap¡¯s with high quality Nichicon brand. 105c temp range and if exact values cannot be obtained you can up the microfarad value up 5% and you can double the voltage rating. Removal and replacement is very difficult if you don¡¯t have the proper solder/desolder unit. Don¡¯t overheat the circuit board.

Craig

On Mar 30, 2018, at 1:42 PM, fgswww@... wrote:

Hi, I m from Argentina. I m repairing a 2445B. When I turn on it, the panel control lamps flashing one time only. The TRC never drawing anything.
I check the J119 voltages, for example....pin # 1. (-15V) I read -14,6V (+/- 0.2V) pin #8 I read 82V (+/- 0.3V) etc etc etc. The readouts are nearby but are not exactly.

Any suggestions?

Thanks.-
 

Craig gives good advice for the long term but I doubt it will fix the current problems.? You say the voltage measurements are near (+/- 5%).? That means the scope should run, just not be accurate in its measurements, timing or amplitudes.? Since the panel lights flash once, then nothing more its likely the problem is in the processor board.? Proper turn on sequence is for the lights to flash, then sequence through the channel indicators (ch 1, ch 2, ch3, ...) then finally stop at one of the lights lighted (an error condition, the lighted light indicates the error) or with all the panel lights in an operational state (completed power up).? Your scope does neither.? My bet is the A5 processor board has failed.? A VERY common failure is leaking capacitors destroy some surface mounted resistors on the A5 board.? You will need a service manual to trace and debug this fault.? I fixed exactly that on a 2445B today.

On ?Monday?, ?April? ?2?, ?2018? ?10?:?02?:?09? ?PM? ?CDT, Craig Cramb <electronixtoolbox@...> wrote:

Power supply voltages are very important. I would recommend disassembly of scope and remove PS as a unit. Pay very close attention to the wiring connections. Then separate the inverter? and regulator boards. Start replacing the electrolytic capacitors. C1220,C1240,C1260,C1280,C1300,C1330,C1350 on the regulator board.
Then C1111,C1110,C1102,C1101, C1113,C1116,C1114,C1115,C1132,,C1120,C1130, C1072,C1066.on the inverter board.
You will definitely need service manual to ID these parts. Match the cap¡¯s with high quality Nichicon brand. 105c temp range and if exact values cannot be obtained you can up the microfarad value up 5% and you can double the voltage rating. Removal and replacement is very difficult if you don¡¯t have the proper solder/desolder unit. Don¡¯t overheat the circuit board.

Craig


On Mar 30, 2018, at 1:42 PM, fgswww@... wrote:

Hi, I m from Argentina. I m repairing a 2445B. When I turn on it, the panel control lamps flashing one time only. The TRC never drawing anything.
I check the J119 voltages, for example....pin # 1. (-15V)? I read -14,6V (+/- 0.2V) pin #8 I read 82V (+/- 0.3V) etc etc etc. The readouts are nearby but are not exactly.

Any suggestions?

Thanks.-
 

Hey there fgswww(?),

Look at page 6-13 of the service manual, where it describes the "Kernel
Tests" and "Exerciser Routines". The front panel LEDs likely have a message
for you relating to the specific failure the MPU has detected.
If you can post a video of the front panel as the scope is powered on, we
could help decipher the message, and/or verify your decoding...

Siggi

On Mon, 2 Apr 2018 at 19:50 <fgswww@...> wrote:

Hi, I m from Argentina. I m repairing a 2445B. When I turn on it, the
panel control lamps flashing one time only. The TRC never drawing anything.
I check the J119 voltages, for example....pin # 1. (-15V) I read -14,6V
(+/- 0.2V) pin #8 I read 82V (+/- 0.3V) etc etc etc. The readouts are
nearby but are not exactly.
 

On Tue, 3 Apr 2018 at 10:29 Siggi <siggi@...> wrote:

Hey there fgswww(?),
Ah, Fernando it is, my apologies for not noticing your name in the from:
field.


Look at page 6-13 of the service manual, where it describes the "Kernel
Tests" and "Exerciser Routines". The front panel LEDs likely have a message
for you relating to the specific failure the MPU has detected.
If you can post a video of the front panel as the scope is powered on, we
could help decipher the message, and/or verify your decoding...

NB: My 2430 was in a bad way - eventually I found it was bad RAM. It gave
me occasion to exercise the MPU diagnostic jumper. On the 2445B, that'd be
P503. When you flip it to the "DIAG" setting, the MPU reads a NOP
instruction hard-wired to the data bus. This causes the MPU to generate
read cycles for the entire address space, which allows you to verify that
the MPU is working to some extent, and to verify the address decoding logic
against a repeating access pattern.

Do you have a second scope to turn on your 2445B?

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