Yamaha HTR-3064 receiver partial recap
Problem statement
Device
Yamaha HTR-3064 receiver, version G (Europe)
Symptom
The unit powers up just fine, but when an HDMI source is switched on, the unit turns off. Upon the next power-on, the display indicates a PS PRT alert protection, with a numeric indication between 098L and 100L. This does not happen, however, if the unit is powered up and left for 15-30 minutes to heat up before switching on the HDMI source.
With the unit idle (no HDMI source active), enabling the self-diagnostic function and monitoring the PS voltage shows values varying significantly between values below 120 and slightly above 130.
Background information: the PS value
PS appears to be an internal A/D monitoring point that averages several voltages in the power supply chain. From the Service manual (p. 37):
PS: Power supply voltage protection detection
Detected: AC2, ±12A, S9, +7D, +5A, +5I, -VP
Detection port: 93 pin (PS_PRT)
Normal value: 101 to 155
(Reference voltage: 3.3 V=255)
which indicates that the normal range at that point is between 1.31 V and 2.01 V (circuit diagram mentions 1.7V). A 098 reading would correspond to 1.27V, a 100 reading to 1.29. So the observed PS shutdowns would correspond to undervoltage by a good fraction of a volt at this test point.
Service manual oddity
In the documentation of messages displayed when starting the self-diagnostic function, the HTR-3064 service manual lists a number of possible protection faults at previous shutdown, with associated messages displayed on the device shown as illustrations.
| Paragraph | Fault | Message from illustration |
|---|---|---|
| 2-1 | Excess current | PS_PRT (with ADC reading) |
| 2-2 | Short between speaker terminals | I PROTECT |
| 2-3 | Abnormal DC output | DC_PRT (with ADC reading) |
| 2-4 | Abnormal power supply voltage | PRV_PRT (with ADC reading) |
| 2-5 | Excessive temperature | TMP_PRT (with ADC reading) |
The ADC conversions (section 9 of self diagnostics) and the IC221 pin list describe parameters monitored:
| Pin | Pin name | Description |
|---|---|---|
| 53 | I_PRT | Overcurrent protection |
| 93 | PS_PRT | Power supply |
| 87 | DC_PRT | Power amplifier DC output |
| 89 | THM1_PRT | Temperature |
| 90 | THM2_PRT | Temperature (U and C models) |
Examination of the circuit diagrams confirm that the PS_PRT pin indeed averages the voltages of various test points in the power supply section. So it looks like the wrong messages might be shown in the description of self-diagnostic conditions, and PS_PRT: xxxL on the display would indicate undervoltage in the power supply section (i.e. should be shown to illustrate 2-4 and not 2-1).
Interestingly, no ADC pin of the CPU is labeled as PRV_PRT.
The service manual for the HTR-3067 has very similar text, but shows the PS_PRT illustration for the “abnormal voltage in power supply” condition, which contributes to confirming the logic here:
Investigation
Visual inspection
Opening the case reveals two swollen electrolytic capacitors C1317 and C1320 on the OPERATION (2) board.
Both are smoothing capacitors located right after rectifier bridges fed from the main transformer.
- C1320 is 10,000 µF and smoothes the +7D rail monitored by PS_PRT.
- C1317 is 4,700 µF and smoothes the input of IC132, a 7805 regulator providing the +5I rail also monitored by PS_PRT.
In-circuit measurement
In-circuit measurement of course cannot provide reliable component values but suggested that the capacitance for both caps was way off. By comparison, measurement for other caps on the board (C1318, C1319) showed values within range of the nominal ones.
Out-of-circuit measurement
Once the two swollen capacitors were desoldered (using a power desoldering pump, which posed no difficulty), out-of-circuit measurement confirmed values way off the nominal ones, as well as substantial voltage loss. The ESR figure was not remarkably high, but still one order of magnitude higher than the one observed on new replacement parts.
Parts replacement
I ordered replacement caps from Reichelt, which has the lowest shipping rates for small orders among reputable online sellers. I wanted to avoid cheap Chinese knockoffs this time, as I don’t fancy going through the whole repair process too often.
Component tester readings for the replacement parts
Soldering new caps
Soldering the two new caps in place proved more difficult than anticipated. The solder tended to ball instead of flowing nicely onto the pads. This is likely due to using too high a temperature on the soldering iron, resulting in burning the flux before it had a chance to actually remove the thin oxydization layer on the pads. Light scraping of the pad with a fiberglass abrasive pen likely would have helped as well.
Post-repair testing
Once the two new caps were installed, the readings for the PS ADC value in the self-diagnostic function became much more stable, both before and after switching on the HDMI source. It remains in the vicinity of 130, consistent with the expected 1.7V (reading 131) shown on the service manual circuit diagram.
The amplifier no longer shut down upon connecting an HDMI signal: repair was declared successful.