Hello everyone, I’m pretty new to analog electronic and I bought this VOC 5 scope to get started.
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This is actually a rebranded Trio-Kenwood OEM and I’m pretty sure it’s a CS-1560A. The unit does not work, all I can get is a dot on the CRT that I can move on the X and Y axis.
I have a gut feeling the problem might be damaged transistors and ICs, and after looking online it appears some are well known to age poorly (getting noisy and opening). The problem is, those are pretty much discontinued Japanese models and I can’t find much consensus to what proper replacement to use. I saw some audio folks suggesting some replacements but nothing 1 to 1.
While I can’t say yet if the semi conductors are the real culprits, I’d love to have moderns substitutes for them as well for the ICs, so I could make a small stock of them to keep the equipment running for years to come, but some are simply completely obsolete. Ideally I’d use either BC/2N/BSS transistors and 74HCT but that probably very optimistic.
According to the datasheet I found, those are the models.
BJT:
- 2SA733-Q or R
- 2SC1419-C
- 2SC1507
- 2SC154-C
- 2SC458-C
- 2SC45B-C
- 2SC535-B
- 2SC983-Y
- 2SC9B3-Y
- 2SD401
JFET:
- 2SK30A-GR
- 2SK30A-O
ICs:
- RC455BT
- RC733T
- TD-3400AP
- TD-3404AP
- TD-3472AP
The TD-34 parts seems to be Toshiba ripoff of the SN74 counterparts in open collector configuration, including the very obsolete 7472.
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I also wonder, since JFET are rather nice these days, could it be possible to replace them with depletion mode N-Channel MOSFETs?
And regarding electrolytic capacitors, should I replace them with modern electrolytic or with solid polymer equivalents?
I’d really like some advises to how to proceed with a project like this.
Thanks
Hello Grump. What you have is a repair project indeed & it is one that’s going to need an approach that involves locating the actual fault & addressing it, be it finding out you need specific replacement part(s) or perhaps that there may simply be a dirty selector switch that is not allowing the Timebase to function.
Some questions:
Have you found the full service manual that matches your ‘scope? (I have located one for the CS-1560A on BAMA).
What test gear do you have access to use? (Being able to prove 100% that, as example, a transistor is completely failed etc).
How much experience do you have doing fault finding, identifying a component is truly failed & successfully substituting for it if you cannot locate another original? This will need an understanding of how a ‘scope works in general terms anyway but to be able to recognize what the circuit is meant to be doing & to some extent the service manual shows this in the Circuit Description.
Your biggest hurdle is that your oscilloscope is in fact a test instrument as opposed to say a vintage hifi stereo amp or an old radio. So you will be dealing with very high voltages for the CRT & some specific waveforms, meaning you will likely need another ‘scope to locate what’s not working properly. Interestingly the service manual has an indepth trouble shooting section guide.
So, FWIW may i suggest you do not approach it as so many folks appear to be doing with vintage hifi stereos and adopt the Cult-like belief of doing no testing but to embark upon replacing all the capacitors then all the semiconductors as the path to a repair!!! As a test instrument it will have reasonably high quality very specific components so best not to go firing off the parts cannon if you get my drift..
All that said, bringing an older ‘scope back to life & verifying its calibration is okay so it can be used at the bench can be a truly rewarding experience in this hobby. Best of luck with it & feel free to continue to reach out…
I located the manual and schematics indeed.
My test equipment right now are a multi-meter (Brymen BM235, a sort of mid range option), I have a cheapo capacitor tester and a component identifier thingy FNIRSI LCR-P1. I should be able to use the diode mode and read the junctions of the transistors, however I read somewhere it’s not always reliable to do that in circuit.
As for experience, well, I know a bit of digital electronics, I designed some logic gates out of discrete components and made some circuits with ICs, but not much in analog trouble shooting. And to be honest, I’m not skilled enough to understand the schematics of the scope. I know how to use a scope but the circuitry is quite complex to me.
So I checked just three transistors on the PSU board in circuit, and the two 2SC1419-C have weird readings.
The voltage drop between B->C and B->E are around 0.5V which is already low but worse, they have reverse voltage drops ranging from 0.58 to 1.14V. I guess I’ll have to take them out of the board and check them again just to be sure there isn’t some on board mambo jumbo that give such readings. Otherwise if the PSU itself is bad, that certainly would explains a few things.