Re: TM506


Andy Warner
 

WRT extenders, following advice here, I picked up one of these:

https://www.ebay.com/itm/401747463642

Some quality time with a dremel to cut the slot in the PCB, and removing a
few wires on what form the high numbered pins (which I left unconnected.)
Works great, and the price can’t be beat.

On Sun, Jul 19, 2020 at 19:00 Tom Miller <tmiller11147@comcast.net> wrote:

I might add to Harvey's comments. Do an ohmmeter check of all the
supplies first to rule out shorted supply busses.

Regards

On 7/19/2020 7:46 PM, Harvey White wrote:
Plugin gets Hot:

check for shorted tantalums. Check power supply voltages first.

The TM5000/500 series does not use regulated supplies (except for some
in the TM5000). The plugins rely on 1) knocking down existing bulk
voltages with on board regulators. 2) using the PNP and NPN pass
transistors on the frame as regulating elements with the controls on
the plugin. 3) using the uncommitted transformer windings to make a
raw DC voltage that gets regulated down to something.

Separate transistors (PNP/NPN, one pair) per slot. Separate
transformer windings (isolated) per slot. Common bulk supplies.

The mantra of fixing stuff is that the power supplies have to be OK
first. This includes ripple. Had a 1000 volt calibrator that
wouldn't go above 250 volts. Finally figured out that the circuit
could regulate ok if the voltage was 250 or less, but couldn't get
higher. Replace one of the main filter capacitors and things were ok.

Not the same circuit, but possibly something to think about.

Looked at the waveform. Suspect + supply driving output, shorted
tantalum there, or perhaps bad transistor pulling up the output to the
supply.

Harvey


On 7/19/2020 5:50 PM, Stephen wrote:
Pictures of some wave forms have been posted here in the same folder.
I wrote what you’re looking at underneath each one.

https://groups.io/g/TekScopes/album?id=250733




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