Hello folks,
I retrieved a Tektronix TDS-620B digital oscilloscope from the dust-bin of my university today. The unit is completely dead. Fuse (6A/250V) is ok. The power-supply is really sophisticated and I think servicing it without a service-manual is impossible.
Maybe some of you guys has an idea where to get the manual or what could be the culprit. There is a sticker which shows all output voltages of the power-supply, but I have no idea where to test them.
Any hints ?
Adrian
Adrian Glaubitz wrote in news: snipped-for-privacy@z6.physik.fu-berlin.de:
the TEK "service" manual is for module exchange only. there will be no component-level schematics or parts lists. AFAIK,the power supply was a purchased part.
yur model is out of support;that is why they threw it away;parts or exchange assemblies are no longer available.
(their site sucks,too.they don't even tell you anymore when it went out of support)
-- Jim Yanik jyanik at kua.net
On Jul 7, 9:31=A0am, Adrian Glaubitz wrote: > Hello folks, >
Just this morning I had a Tek PAL sync generator that refused to start because of a high ESR 100uF cap in the power supply. Also, early 1700 series waveform and vectorscopes will fail to start when a 10 uF cap goes bad. Since it isn't blowing fuses, it doesn't have blown up power devices - though they still may be bad. Checking power supply caps for ESR may be a good start.
G=B2
university today. The unit
sophisticated and I think servicing
the culprit. There is a sticker
to test them.
ok, I got somewhat further. I found a fusible resistor to be blown, R176, 18 Ohms. It was completely open, I tested it outside circuit. The unit still doesn't power up though. I already checked the transistors at the heat-sinks with a diode-tester and they appear to be okay. Furthermore I can measure 300V DC at the output of the rectifier. Any more hints ?
Thanks !
Adrian
university today. The unit
sophisticated and I think servicing
the culprit. There is a sticker
to test them.
Are you sure it's *completely* dead? I'd probe it's outputs with another scope to be sure. You may be able to see it pulse it's outputs in an attempt to power up before shutting down. If you do see pulses on the outputs, it could just be a matter of high ESR capacitors.
Also, try disconnecting other boards/modules in the unit. One of them could be overloading the power supply.
Hi there,
Yes, it is completely dead. I followed the troubleshooting procedure step by step from the "service-manual" (they don't have schematics) from Tek and from the flowchart it said "replace PSU".
I did some more testing today. It appears, that after the blown resistor there is an PWM-circuit with a TOP200YAI PWM-Switch. After replacing the resistor I can read the 300V at the input of the PWM-circuit, but there are *no* 5V DC at the output. I did a web-search for the PWM-Switch datasheet and found it. It actually contains a schematic for a typical application and the PWM-circuit in the PSU appears to be completely identical.
I tested all diodes, resistors and the windings of the transformer in the circuit and all parts indicate ok. So I presume the PWM-Switch itself to be bad. The thingy costs about 8 US-Dollars and I only can find a TOP201YAI and TOP204YAI at my local dealer. Can I use those or does it have to be the 200 ? Anyone knows where I could rip one out ?
I'd be interesting if anyone could comment on this :-).
Regards,
Adrian
Adrian Glaubitz wrote in news: snipped-for-privacy@mid.uni-berlin.de:
check their datasheets.I suspect the TOP201 will work fine.
high ESR of the electrolytics is a big problem area in switchers.
-- Jim Yanik jyanik at kua.net
Just for the records. It was the TOP200YAI that was shot. Replacing that one and the Tek would fire up again ;-). Now it's just complaining about some calibration error.
Adrian
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