开云体育

Hello, I aquired 468 scope in mint condition, but with some problems..,

1. first power on, LEDs and fan working, but no traces, no HV voltage.., HV F809 fuse blown, Q1108 blown, L107 shorted
Replaced fuse, transistor, coil, C104, C108 tantalum and CR104 burned diode.
CRT started working, but after warming (about minute) the brightnes increase and few moments later traces start blinking .., all basic voltages 55+, 110+, 5+, 8- is in tolerance, +15v rail measured 22V

Can you help me ? PS , sorry for english ..

Martin

Martin,

The high brightness is likely bad d-c restorer diodes being leaky. Replace them with 1N4937. Also replace the 22meg 1/4W carbon resistor near that circuit with a Vishay VR37. This is a 1/2W 1% type. The original is highly likely high in resistance. When this resistor is high in value, the trace will be bright then dim as it warms up over 10-20 minutes without touching the intensity control.

The 15V regulated supply at 22V is likely a shorted series pass transistor, Q701. It could be a bad IC, U712B. also replace the zener, VR725 with a BZX85B9V1 (this type is VERY likely open) and change R726 to a 6200ohm 1% 2W type (about 16mm or larger length). The original resistor is 1/2W and likely burned, brown body, and out of tolerance. I have seen this resistor in this circuit bad enough times to change it on sight. Mouser has the parts, except for the 6200 ohm 2W resistor. That is available on ebay.

Mark

Martin,

I forgot to say that if your scope and any other Tek. items have any 151-0367-00 transistors, check them. These are likely leaky from C to E as a diode. Any of these that have round leads will be leaky. Replace the leaky ones with KSP10BU. These have a pinout of BEC. I have found that leakage to cause problems until they were replaced. Mouser has these transistors.

Mark

thank You Mark,

My bad about +15V, is not regulated rail, but unregulated +15V.., shows 22V. Waveform 161 indicate, thats ok, (21-21.8V)..
Others tips i will check soon ..

Digital section is death, one PROM has bad CRC, ..