Kikusui COS6100M Oscilloscope

It would have helped to have the part numbers. U1211 is a upc4558, a gumdrop dual Op Amp. One half is used for the + 5VDC rail. The other half is in the + 55 VDC rail. U1212 is a TA7199P, which is a dual, tracking voltage regulator. that provide the + and - 12VDC rails.

Do you have a working scope to troubleshoot with? Have you tested the bridge rectifiers? Which volatge are you measuring?

Manual at:

Thank you for adding the part numbers to the post. I do not have a scope. I am measuring the +150, +55, +21, +12, +5 and -12 rails.

How would you proceed without a scope?

Are they all changing about the same percentage? That would indicate a problem with the transformer or line wiring.

That was my thinking as well, especially since the PS is divided into 3 discrete circuits. The line side is steady at 120V. The voltage adjustment plug is set correctly. I reflowed the transformer connections but no joy.

John Keiser wrote: ==================

Do you know how to even use this scope ?

..... Phil

The power supply voltages are way off and unstable. I'm helping him by email.

the PS outputs 150V, +/-12, +5 vdc. Do they *all* drop 50%? All rise 15% no load? If so, that suggests a bad transformer or perhaps a bridge rectifier lost a leg. a scope would help with diagnosing the rectifier. Actually don't even need a scope for the BR. DMM will work. Looks like everything else in the PS can be troubleshot with a DMM & ESR meter for finding bad caps. BTW IC u1212 is a TA7179 (not 7199)but it is a dual track regulator. Interesting that they use the sense lines. J

I misread the part number on the schematic. I am currently waiting for cataract surgery on both eyes. The other voltages are referenced to the +/- outputs of the TA7179P. I've never seen a regulator with tracking inputs that could be left floating.

Via email he said that there is 40 volts of ripple at C1213.

snipped-for-privacy@gmail.com wrote: =======================

That cap is open cct. Would explain a great deal of no sweep.

..... Phil

With the excellent advice and encouragement of Mr. Terrell I believe the problems are caused by a defective regulator IC [TA7179P]. The part is long obsolete but before brewing a work around [same IC fails in arcade games and Roland devices] I will wait for a Chinese IC marketed as a replacement. [Fraud for $2? Maybe.] I will report back with the result next year.

I'd be inclined to just do an easy work around. Two 12V (7812/7912) ICs can do all of that with almost no rewiring, particularly if you don't need the supplies to be adjustable. The two ICs will even mount on the heatsinks in place of those two regulator transistors.

Two issues. Two separate regulators don't track, and the 1A limit may be too low.

Non tracking regulation can case excessive drift and affect gain problems in the Vertical amplifiers.

A good lab grade bench supply could be used for testing, but I wouldn't use one rated at under 3A

I've done a lot of work on complex Dc circuits where a small difference in the supply rails from what was specified will cause it to fail. The required bench supply was to the milivolt, to achieve the maximum allowed1.5 milivolt at the output of the 14 op amp gain control subsystem. Your test equipment has to be better than what you work on.

Ali Express delivered on a TA71170P IC yesterday. Nicely packed from Tajikistan. Possibly not genuine Toshiba. I replaced the original suspect and the oscilloscope now has a responsive trace. To soon to say what else might need fixing but this is major progress. Thanks for the kind encouragement.

Paid from the $800000 the Taliban mistakenly sent them?