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Reader Question · Fox Tango International
Why Does My FT-2000D Only Make 100 Watts?
Diagnosing the half-power Yaesu FT-2000D — the 50 V PA rail, the SD2931 finals, ALC drift, and the misidentification trap.
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| “I have a Yaesu FT-2000D that is supposed to put out 200 watts, but on every band it only makes about 100 watts into my dummy load. The RF power control is wide open and the radio otherwise transmits and receives fine. Where do I start looking?” |
This is one of the most common questions in the Fox Tango International community, and the symptom — exactly half the rated output — is a useful clue rather than a vague complaint. A radio that makes some power but not full power is rarely a dead final stage. More often it is a supply, calibration, or single-device problem, and on the FT-2000D specifically there is a small list of usual suspects that the rig’s own architecture points you toward.
Before touching a soldering iron, it pays to understand why the “D” makes 200 watts and the plain FT-2000 makes 100. That single fact reframes the entire diagnosis.
The “D” is a different PA — not just a bigger power supply
It is widely repeated that the FT-2000 and FT-2000D are “the same radio,” differing only in that the D ships with an external supply. That is half true, and the half that is wrong is the half that matters when you are chasing power output.[1]
The standard FT-2000 has an internal supply and a 100 W power amplifier. The FT-2000D ships with the external FP-2000 supply, which delivers two rails — approximately 50 V at 10 A for the PA and 13.8 V at 5 A for the rest of the transceiver — and feeds a physically different 200 W amplifier board.[2] Yaesu’s own service documentation makes the distinction explicit by calling them two separate assemblies:
| FT-2000 — PA-A (100 W) | FT-2000D — PA-B (200 W) | |
|---|---|---|
| Final devices | RD100HHF1 push-pull pair (Q5009 / Q5010) | SD2931 push-pull pair (Q5515 / Q5516) |
| Driver | RD16HHF1 (Q5006 / Q5007) | SD2918 (Q5514) |
| PA drain rail | From the internal 13.8 V supply | Dedicated 50 V rail (FP-2000) |
| Rated output | 100 W (AM 25 W) | 200 W (AM 25 W); 75 W Class A |
Device and assembly identities are taken directly from the Yaesu / Vertex Standard FT-2000/D Technical Supplement, which lists the PA-A and PA-B units as distinct boards with separate parts layouts and separate alignment procedures.[3] This lineage — a high-voltage MOSFET output stage fed by an external supply to reach 200 W — goes all the way back to the FT-1000 series and the MARK-V, which used a 13.8 V rail plus a separate higher-voltage rail for the output devices.[4]
| Why this matters: because the SD2931 finals develop their power from the 50 V rail, anything that compromises that rail — a sagging FP-2000, an undersized substitute supply, or a bad connector — robs the PA of headroom and the output collapses toward 100 W. The number “100” is not a coincidence; it is roughly what is left when the 50 V advantage is taken away. |
The most likely causes, in order
A radio that makes a clean, stable ~100 W on all bands narrows the field considerably. Work down this list before disturbing anything internal.
1. The 50 V PA rail is sagging or partly missing
This is suspect number one. Under key-down CW into a dummy load, measure the 50 V rail at the PA board (and at the FP-2000 output). A rail that reads near 50 V at idle but slumps to 35–40 V the instant you key is the classic signature: a tired FP-2000, an inadequate non-Yaesu substitute supply that cannot source the full PA current, or voltage lost across an oxidised connector, fuse, or harness pin. If the 50 V rail were entirely absent the SD2931 finals would make almost nothing — so a partial rail is exactly what produces a clean-looking half-power result.
2. ALC / power calibration drift or a menu limit
If the ALC clamps early, the rig will hold output near 100 W even though the PA hardware is perfectly capable of more. Watch the ALC indication while keyed: does it rise smoothly, or slam to the limit abruptly and early? Corrupted internal alignment values, a previous owner’s “adjustments,” or a power-limit menu/QMB profile can all cap output. Confirm the RF power control is genuinely at maximum and that no memory or menu profile is holding it down.
3. One weak or failed device in the push-pull stage
A push-pull final with one degraded SD2931 — or a weak driver — will make reduced power, though the drop is rarely a tidy “exactly half” and usually comes with asymmetry or distortion. This is confirmed by drain-current measurement rather than guesswork: the FT-2000/D has a documented ID (drain-current) meter alignment for the 200 W type and a VDD adjustment, so you can verify bias and current sharing against the service procedure.[5]
4. It is actually an FT-2000, not an FT-2000D
Do not skip this. Plenty of radios change hands described as “FT-2000D” when the body is a standard FT-2000 with a 100 W PA-A board and an internal supply. A standard FT-2000 making 100 W is working perfectly.[6] Confirm the presence of the external FP-2000 and the 50 V rail before chasing a fault that does not exist.
5. Measurement artefacts — SWR foldback and meter error
Confirm the “fault” is real before opening anything: test into a known-good 50 Ω dummy load, use CW or FM for a steady carrier rather than SSB voice peaks, read with a trusted external wattmeter (not just the internal meter), bypass the internal tuner, and keep SWR near 1:1 so protection foldback cannot be masquerading as low power.
A repeatable bench sequence
The official alignment uses a 50 Ω dummy load and external wattmeter on the ANT 1 jack, so reproduce those conditions and change only one variable at a time.[5]
| Step | What to do | What it tells you |
|---|---|---|
| 1 | Confirm it is a D: locate the FP-2000 and the 50 V connector. | Rules out the misidentification trap entirely. |
| 2 | CW carrier into a 50 Ω dummy load, internal tuner off, external wattmeter, RF power at max. | Establishes a trustworthy baseline reading. |
| 3 | Measure the 50 V rail at idle and key-down at full commanded power. | Significant droop = supply / connector / harness. |
| 4 | Watch ALC behaviour while keyed. | Early/abrupt clamp = ALC or calibration drift. |
| 5 | Check PA drain current (ID) per the 200 W alignment; compare both halves. | Imbalance / low ID = weak SD2931 or bias issue. |
| 6 | Log output on 160 / 80 / 40 / 20 / 15 / 10 / 6 m. | All-band = global cause; some bands = filters / relays. |
| Safety: the 200 W PA chassis carries a 50 V rail capable of high current, and the FP-2000 contains mains-powered circuitry. The PA-B board is dense surface-mount construction; Yaesu’s own manual notes that servicing it requires experience with SMD work. If you are not equipped to make rail and drain-current measurements safely, this is the point to hand it to a qualified technician. |
If it is low on only some bands
Everything above assumes the radio is down on all bands. If instead the output is fine on some bands and low on others — or if 6 m behaves differently from HF — the cause shifts away from the supply and the finals and toward the band-dependent parts of the RF path: low-pass-filter and band-switching relays with contaminated contacts, PIN-diode or switching elements, and the output network components (transformers, combiners, chokes, matching capacitors). Inspect those relays for tired or pitted contacts and the board for cracked solder joints and heat-stressed pads.
Decision table
| What you observe | Prioritise |
|---|---|
| All bands ~100 W and 50 V rail sags under load | FP-2000 / supply, harness, connectors, PA feed |
| All bands ~100 W, 50 V normal, but low PA current | Bias, drive, ALC calibration, or a weak SD2931 |
| Only some bands low | Relays, LPF, switching diodes, output network |
| Starts near 200 W then falls; temperature-dependent | Bias stability, thermal sensing, marginal joints |
| No FP-2000 / no 50 V rail present at all | Confirm the rig is truly a “D” — it may be a 100 W FT-2000 |
Document as you go
Keep a single band-by-band table as you work. Photograph the boards before changing anything, mark original trimmer positions before you adjust them, and change only one variable at a time so a single result is never ambiguous.
| Band | Fwd power | PA current | 50 V rail (key-down) | ALC |
|---|---|---|---|---|
| 160 m | … | … | … | … |
| 80 m | … | … | … | … |
| 40 m … 6 m | … | … | … | … |
| Bottom line: on an FT-2000D, “exactly 100 watts” should make you check the 50 V rail and confirm the radio is really a D before you suspect the SD2931 finals. The single most common ending to this story is a tired or wrongly-substituted power supply, a connector dropping voltage under load, or a plain FT-2000 wearing a “D” in the advertisement. |
Credits & acknowledgements
Device identities, assembly designations, and alignment procedures are drawn from the Yaesu / Vertex Standard FT-2000/D Technical Supplement — the authoritative source for any work on these radios, and the one document worth obtaining before opening the case. Thanks also to the Fox Tango International Yaesu community, whose members keep these rigs on the air, and to ARRL / QST for the product-review history that documents the FT-1000-to-FT-2000 lineage.
Footnotes & sources
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[1] Yaesu, FT-2000 / D legacy product page — the FT-2000 and FT-2000D are listed as 100 W and 200 W HF+6 m transceivers respectively (AM 25 W). yaesu.com. ↩ [2] FP-2000 external supply ratings (approximately 50 V/10 A + 13.8 V/5 A) and the 200 W / 75 W Class-A figures, with the standard FT-2000 noted as internal-supply / 100 W. RadioMasterList, Yaesu FT-2000 / FT-2000D specifications. radiomasterlist.com. Internal-vs-external supply distinction also per Universal Radio. universal-radio.com. ↩ [3] Yaesu / Vertex Standard, FT-2000/D Technical Supplement. The PA-A (100 W) parts layout lists RD100HHF1 finals (Q5009 / Q5010) and an RD16HHF1 driver (Q5006 / Q5007); the PA-B (200 W) parts layout lists SD2931 finals (Q5515 / Q5516) and an SD2918 driver (Q5514). Hosted at ManualsLib. manualslib.com. ↩ [4] ARRL QST Product Review of the FT-2000, which recounts the FT-1000 lineage and notes that the MARK-V reached 200 W using an external supply providing 13.8 V plus a separate higher-voltage rail for the MOSFET output stage — the same two-rail philosophy the FT-2000D continues. arrl.org. ↩ [5] Yaesu / Vertex Standard, FT-2000/D Technical Supplement, Alignment section: separate VDD (drain-voltage) and ID (drain-current) meter adjustments are specified for the 200 W type, and the power/alignment procedure calls for a 50 Ω dummy load and wattmeter on the ANT 1 jack. manualslib.com. ↩ ↩ [6] A standard FT-2000 (PA-A board, internal supply) is rated at 100 W and is operating to spec when it produces it; the 200 W figure belongs only to the FT-2000D with its PA-B board and FP-2000. eHam.net community reviews collect owner experience across both variants. eham.net. ↩ |
Disclaimer: this article is general reference information for experienced operators and technicians. The FT-2000D PA chassis carries a high-current 50 V rail and the FP-2000 contains mains-powered circuitry — work safely, follow the factory service documentation, and refer the job to a qualified technician if you are not equipped to make these measurements.
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Mike Peace VK6ADA — r-390a.net Administrator Vintage & classic HF restoration · vk6ada.com.au |