HD-1410+TS-520S

[KU0DM]

Hey gang, I recently acquired a TS-520S and HD-1410 to play with. Upon hooking the keyer up to the radio, I get a solid tone. I've isolated it to a short somewhere in the keyer itself, however even after looking at the manual have no idea where I ought to start searching.

Any ideas?

73

[K7SGJ]

Take a look at the transistor that is used to key the rig. That's usually the last transistor in the keyer, and the line that would go to the 520. Usually across the emitter and collector circuits. Sounds like it's shorted. My guess is you tried to key the rig without a buffer stage between the keyer and the 520. For the most part, the keyers are great for a solid state rig, but for tube and some hybrids, the keying transistor won' handle the keying current. Buffers circuits are all over the web. The Heath manual might have a circuit in the in it for use with tube circuits, or describe their recommendations. I don't have a manual handy, so check in yours. Good luck.

[N8YX]

There are a pair of keying transistors in the HD-1410:

Q5, Heath P/N 417-816
Q7, Heath P/N 419-294

These are connected in complementary fashion so the keyer could be used with either grid-block or cathode keyed rigs. IIRC, the '520 is the latter and there's ~ -100VDC present on its key jack. That being the case, I would suspect Q5 to be the culprit. Remove D4 (in series with Q5's collector) from the circuit and see if the condition persists.

[HUGH]

When the jack plug is inserted there is about -65V on the key. Using an electronic key may require a series diode to block this. The user manual insists on -ve keying for electronic keyers. Since my TS520 blew up I sold the manual and am only left with a fuzzy copy on which the schematic lines are hard to follow.