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5328A counter

 

I have recently replaced most of the electrolytic caps and the on/switch on this device.? Instead of inconsistently turning on and off, it will not turn on at all.? The standby light does not? illuminate when the device is plugged in.? I have 120 VAC to the transformer and no voltage downstream the transformer.? All fuses are correct size and intact, no shorts detected at the fuse holders.? I get zero voltage readings at all voltage test points on all pcbs.? I would appreciate any ideas on what may be wrong, what else to test.? This unit is just one more problem from the scrap yard.

Thanks
--
Joe White
KW4YW
 

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Well, assuming you are measuring 120 V actually across the transformer primary windings (BLK/YEL & BLK or BLK/RED & BLK/GRN) and the line voltage selector switch? is correctly set (and working) and there is nothing in the way of an AC voltage actually on the secondary wires out of the transformer, sounds like a transformer winding has failed open circuit, but the chance of that happening exactly when you changed the caps and switch, while possible, I would rate as unlikely?
If there is no secondary voltage and the fan is not running either..... then it's really odd........I think that really means the line/neutral voltage ain't getting to where it should?

On 06/04/2024 14:58, Joe White wrote:

I have recently replaced most of the electrolytic caps and the on/switch on this device.? Instead of inconsistently turning on and off, it will not turn on at all.? The standby light does not? illuminate when the device is plugged in.? I have 120 VAC to the transformer and no voltage downstream the transformer.? All fuses are correct size and intact, no shorts detected at the fuse holders.? I get zero voltage readings at all voltage test points on all pcbs.? I would appreciate any ideas on what may be wrong, what else to test.? This unit is just one more problem from the scrap yard.

Thanks
--
Joe White
KW4YW

 

If you have verified that there is proper voltage at the primary itself, and the absence of any output from the secondary without any shorting of the latter, then I think you're able to draw the proper conclusion. Just make sure you are truly measuring these quantities at the transformer.

Long-working transformers rarely go open-circuit quietly and without olfactory cues. If they do, then it's often something simple, like stress finally breaking a transformer winding lead from a terminal, perhaps due to someone flexing an assembly in the act of repairing something else. Just look carefully and check for such things.

Good luck!

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

On 4/6/2024 6:58 AM, Joe White wrote:
I have recently replaced most of the electrolytic caps and the on/switch on this device.? Instead of inconsistently turning on and off, it will not turn on at all.? The standby light does not illuminate when the device is plugged in.? I have 120 VAC to the transformer and no voltage downstream the transformer.? All fuses are correct size and intact, no shorts detected at the fuse holders.? I get zero voltage readings at all voltage test points on all pcbs.? I would appreciate any ideas on what may be wrong, what else to test.
 

That is a dual primary power transformer, with a selector switch. Dirt contacts in the switch It looks like it is on the rear panel, next to the fuseholder. If run on 240, a single bad winding would kill the transformer, but both would have to be bad? for 120 volt operation. Those slide switches often fail from old age. The grease in them dries into a non conductive film, or causes the plastic to crumble. I've replaced them in a lot of things since the mid '60s.
Do a search for 'voltage selector slide switch' to find ones with the flush actuator.if yours is bad.


On Sat, Apr 6, 2024 at 2:46?PM Tom Lee <tomlee@...> wrote:
If you have verified that there is proper voltage at the primary itself,
and the absence of any output from the secondary without any shorting of
the latter, then I think you're able to draw the proper conclusion. Just
make sure you are truly measuring these quantities at the transformer.

Long-working transformers rarely go open-circuit quietly and without
olfactory cues. If they do, then it's often something simple, like
stress finally breaking a transformer winding lead from a terminal,
perhaps due to someone flexing an assembly in the act of repairing
something else. Just look carefully and check for such things.

Good luck!

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070


On 4/6/2024 6:58 AM, Joe White wrote:
> I have recently replaced most of the electrolytic caps and the
> on/switch on this device.? Instead of inconsistently turning on and
> off, it will not turn on at all.? The standby light does not
> illuminate when the device is plugged in.? I have 120 VAC to the
> transformer and no voltage downstream the transformer.? All fuses are
> correct size and intact, no shorts detected at the fuse holders.? I
> get zero voltage readings at all voltage test points on all pcbs.? I
> would appreciate any ideas on what may be wrong, what else to test.
 

My long-term memory for short-term events could be entirely wrong on this, but I recall working on some 3528As (all ultimately junked out) long ago, and vaguely that there's an "electronic" power switch function in there. IOW, there's a thyristor circuit or relay or something so the power switch on the front is at low voltage, and remotely activates the circuit. I remember thinking it was ridiculously complicated, had lots of problems, and would be unreliable, which was part of the decision process to junk them out - not worth the trouble. I was highly unimpressed with the design and build quality of that product.

Again, I could be all wrong here and may be thinking about something else, but you should thoroughly study the power supply schematics and understand how it all works before digging in too deeply. Good luck.

Ed
 

So I had to look it up after thinking some. The transformer circuit is pretty conventional, so should be easy to troubleshoot. The transformer is always activated, so the OCXO option can run always, and the supply regulators are enabled by the power switch. There is a TRIAC circuit, but just for the fan, so it won't run all the time - only when turned on.

Anyway, you should have raw power whenever the unit is plugged into line. An easy way to trace the action is to unplug it and look at the resistance between the plug prongs and to points inside like the line fuse and voltage selector and so on.

Ed
 

I want to thank everyone for the suggestions.? Based on them I conducted a thorough search of all the pcbs.? I was not only able to determine why the device would not power up (ask me no questions and I will tell you no lies), I also found several things that about to become problems.
--
Joe White
KW4YW

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