Hopefully, you'll identify a power amplifier with a significant DC offset. If so, we'll dig a little deeper.
So, you've measured the DC on CB372 to CB386?
If possible, I would like you to do a "sanity check" by measuring the DC directly (with respect to signal ground) on one of the emitter resistors (R1071 to R1250).
Ok, no point having to dismantle to gain access to the emitter resistors - don't bother with the sanity check.
In my description of power amplifier DC conditions, I forgot to say that the DC voltage on the amplifier output should reflect the DC voltage feed to LH Q1022 via R1053, R1056 by the reference ground (0V). That's why the amplifier output should be at 0V. If not then there's something wrong with the reference ground (0V).
The next step is to check if the reference ground (0V) is elevated or floating (in voltage) with respect to the input ground on any of the amplifiers. For example, looking at previously attached Amplifier DC condition image for the SBR channel, can you measure the voltage on the side of R1056 or R1054 that's connected to the reference ground (0V) & an input ground?
One additional context, "input ground" is any ground that you can connect to that's on the rear panel inputs etc.
| CONN | PIN | DIGIGND | CHASSISGND |
| CB378 | 1 | -2.021v | -1.976v |
| CB378 | 2 | -2.014v | -1.976v |
| CB374 | 1 | -1.565v | -1.535v |
| CB374 | 2 | -1.563v | -1.536v |
| CB376 | 1 | -1.568v | -1.542v |
| CB376 | 2 | -1.568v | -1.542v |
| CB372 | 1 | -1.553v | -1.531v |
| CB372 | 2 | -1.553v | -1.531v |
| CB384 | 1 | -1.554v | -1.538v |
| CB384 | 2 | -1.552v | -1.535v |
| CB386 | 1 | -1.551v | -1.538v |
| CB386 | 2 | -1.549v | -1.535v |
| CB382 | 1 | -1.549v | -1.530v |
| CB382 | 2 | -1.545v | -1.534v |
As shakalnokturn mentioned, recheck the DC offset. Page 23 of the service manual has a table (RHS) with a column "DC Offset Confirmations" & it shows a DC offset of between 0 to 100mV (i.e. 0.1V).
You might also need to confirm that protection override enables the output muting/protection relays so that the DC offset can be measured at the speaker outputs. If the relays aren't energised, measuring at the speaker outputs would give erroneous results i.e. use the test points instead.
I admit I've been skimming over this rather than thoroughly reading so sorry if I've missed something on the way.
Have you been able to confirm lack of DC offset on all outputs (measuring at speaker outputs) with protection override?
If you're sure the DC output is within tolerances your last remark on reference voltage may be the way to go.
I recently repaired a Yamaha HTR something that was throwing random Power Supply and Thermal protection errors on startup although everything was in range.
A tiny 3.3V SMD regulator on the small signal board (CPU / HDMI...) was giving a low voltage that was used for protection references.
In this mode there is negative DC voltage between all of the 7 outputs and ground that are all the same except for one. I have -5.8v on all channels except "surround back / bi-amp L" which is about 400mV off, at -6.25v.It's surprising that on the speaker outputs it's -5.8V and on the test points it's approx -2.0V. Did you measure a test point & a speaker output at the same time/conditions? It probably doesn't matter i.e. I think it has DC offset problem (which still needs to be investigated).
QuoteIn this mode there is negative DC voltage between all of the 7 outputs and ground that are all the same except for one. I have -5.8v on all channels except "surround back / bi-amp L" which is about 400mV off, at -6.25v.It's surprising that on the speaker outputs it's -5.8V and on the test points it's approx -2.0V. Did you measure a test point & a speaker output at the same time/conditions? It probably doesn't matter i.e. I think it has DC offset problem (which still needs to be investigated).
The DC_PRT protect is a single analogue signal representing the sum of all the channels (via R1152, R1120, R1189, R1047, R1258, R1077, R1221). The controller can't discriminate between channels & will just shutdown the amplifier. I wonder if "DC_PRT: 0L", the "0L" actually means overload i.e. beyond the ADC range. If the DC_PRT is really 0V, you would think it would come out of protection (despite the real dc offsets on the outputs).
I'll have to look into the "DC: 0" error & see what it means.
By the way, I did check the schematic for what shakalnokturn mentioned i.e. 3.3V regulator & reference voltages. This amplifier does have something similar (see attachment). I don't think it's the problem but the information is there if you wish to check.
I too doubt that the 3.3V could be the problem here as Vref is common to CPU Vcc you'd be experiencing other troubles if it was bad, besides for DC protection to give false low readings Vref would have to be too high.
I'm back to NHcoder's first impression:
Very unlikely to have a DC offset related to a fault on every channel (although not impossible), this is more likely a ground / amplifier power supply problem. It's possible you may also have a different problem on surround back L that would need addressing later.
Does this model have a cut-out in the bottom frame that would give access to the relay PCB solder side?
Maybe worth doing a continuity check between all grounds that should be common starting from transformer center point to speaker negative terminals, power amp's then check power stage supply voltages.
I'd have to get more involved and download the service manual, that's not happening on my smartphone...
The reference ground (0V) for SBR, SR, FR is via W1042 & for C, FL, SL, SBL is via W1041 i.e. completely different connectors (so if it's missing, then it's further back). I think the voltage sanity check is needed just to "tick the box".I think I can probe both of these without difficulty. We're talking about checking continuity/resistance between chassis ground and the "E" marked pins on those two connectors, correct? I can see on the schematic for MAIN(2) for example, for W1042 that this ties ground together a bunch of emitters and what appear to be filter caps.
PS I hope I don't sound too abrupt. I am an Engineer (retired) i.e. "on the spectrum".
We're talking about checking continuity/resistance between chassis ground and the "E" marked pins on those two connectors, correct?(learning how to quote, I don't know how to the get the originators name in there)
QuoteWe're talking about checking continuity/resistance between chassis ground and the "E" marked pins on those two connectors, correct?(learning how to quote, I don't know how to the get the originators name in there)
[/quote][quote author=alanep]
Yes please, if you can measure the resistance between the "E" pin on W1041,42 and chassis ground.
[/quote]
Yes please, if you can measure the resistance between the "E" pin on W1041,42 and chassis ground.
Please note incorrect W1041. Should be W1043. Fixed in original posting.
Continuing on with power amplifier power supplies, there are actually 4 feeds to each power amplifier. There's +/-56V unregulated to the outputs and also a +55.6V and -53.8V (from regulators) to the driver stages.
I've got a hunch, it could be one of regulators...
I've updated the previous post to include the schematics.
If you want a break for the night (not sure what time it is there, 3:30pm or so here). I'll be away tomorrow (bushwalking).
I think there's something to go on with.
Ok, it's up to you but mistakes get made when you're tired...
With those voltages (I'll try quoting eventually), there's definitely something wrong with the output of the regulator.
I'll have to look at the layout as where the regulator actually is (updated: page 116).
The regulator is a discrete design but there are a couple of things:
1. The negative regulator mirrors (almost) whatever the positive regulator is outputting.
2. The positive regulator output voltage can be changed by a signal "AMP_LMT"
Updated:
If the "AMP_LMT" signal goes to 0V, it will turn off Q1096 & subsequently the series pass Q1009 i.e. shutting down the regulator.
Updated:
So if possible, the "AMP_LMT" voltage should be measured. It's on W1041 pin 3. Component overlay - Main(3) (page 116 with page co-ordinates C6)
If you go to the trouble of disassembling also check R1008, R1009 (they are fuses), R1283, R1285, R1288 just because high value resistors tend to go open with such voltages.
There's still something strange, even with 1.8V (in lieu of 3.1V), the positive regulator should keep same the ratio i.e. 3.1V reference produces 56V, then 1.8V should produce 37.8V (which it's not doing).
Q1096 is probably in the bowels of the amplifier but it might be worth removing and testing. Do you have anything to check transistors?
Possibly another way of testing Q1096 without having to remove it. The idea is to deliberately feed it with 3V. You'll need to disconnect the IC908 pin 4 (ARM_LMT) wire from CB909 & use the wire to feed 3V (maybe 2 x 1.5V batteries) down to Q1096's base
If you go to the trouble of disassembling also check R1008, R1009 (they are fuses), R1283, R1285, R1288 just because high value resistors tend to go open with such voltages.
So maybe bite the bullet, skip the testing of Q1096 and go straight to R1009 - all the dots do seem to be lined up (& while you're in there, check R1008, R1283, R1285, R1288 as per shakalnokturn's suggestion).
This is a slippery one. From my point of view, it is behaving like the regulator is not receiving power hence the focus on R1009. Can you continuity check that one side of R1009 is connected to B+ (same positive supply as output transistors)?
Not sure if B+ was actually tested i.e. the main +56V rail.
I'm away now for 10 hours or so (hiking/bushwalking).
I then tried activating the transistor Q2004 with 3.3v through a 1n4001 on the PRY pin. This pin says it takes 2.7, which itself comes from a diode at the 3.3v output of an IC on another board. I figure the 1n4001 would be ok as it has a drop of about 1.1v, but maybe 2.2 isn't quite high enough. I was hoping to hear an audible click from the relay that Q2004 is controlling, which activates the main power transformer, but got nothing.You could put 3.3V or more (see below) on the Power (1) PRY pin (W2505) as long as the cable is disconnected from the connector (so it can't back feed to whatever is driving it). Q2004 base current is limited by R2050 (page 139) i.e. it's not critical although it's best not to go lower than the original 2.7V or higher than say 5.5V. The Power (1) board has got mains potential so please be careful.
I had the same problem with my Yamaha receiver.
Unfortunately my patience was less and I decided to break the problem into two logical parts.
(Attachment Link)
Obviously there is more to this story than just being clumsy. I just gave up on Yamaha amplifiers and switched to a different brand.
I will use the Amplifer and Power section somewhere else.
I'm back from the bushwalk so I'm a bit stuffed but I did think of a few things.
Firstly, in relation to turning on the power transformer:I then tried activating the transistor Q2004 with 3.3v through a 1n4001 on the PRY pin. This pin says it takes 2.7, which itself comes from a diode at the 3.3v output of an IC on another board. I figure the 1n4001 would be ok as it has a drop of about 1.1v, but maybe 2.2 isn't quite high enough. I was hoping to hear an audible click from the relay that Q2004 is controlling, which activates the main power transformer, but got nothing.You could put 3.3V or more (see below) on the Power (1) PRY pin (W2505) as long as the cable is disconnected from the connector (so it can't back feed to whatever is driving it). Q2004 base current is limited by R2050 (page 139) i.e. it's not critical although it's best not to go lower than the original 2.7V or higher than say 5.5V. The Power (1) board has got mains potential so please be careful.
To check that RL201 is operating, I can think of a couple of options:
1. You could measure Q2004's collector voltage which would also indirectly measure the relay coil voltage.
With PRY 0V, the Q2004 will be off & its collector voltage should be 5.5V (pulled up by the relay coil) & since both RL201's coil connections are at 5.5V, it will be de-energised (no current flowing through the coil). With PRY 3.3V or higher, it's collector voltage should drop to 0V i.e. one connection of RL201's coil will be at 5.5V and the other connection (Q2004's collector) will be 0V i.e. in theory, the relay will be energised.
2. Find a reasonably safe low voltage secondary and check it with a multimeter on the ACV range (must be on AC volts). The Video (2) board (page 142) has transformer secondaries on CB351, CB352 & Video (3) C351 (also on page 142).
Changing subjects, I assume the amplifier is still disassembled?
I had a think about this apparent loss of voltage to Q1096. In addition to R1009 (which frustratingly is OK & you confirmed it is definitely physically connected through to C1105), there's a couple of other possibilities:
1. R1280 - a 5K6 resistor on Q1096's collector, could you check if it's open circuit? If it's open, Q1096 won't get power & it also won't turn on Q1009.
2. Q1009 - check for the base - emitter diode (& might as well check for base - collector diode). If B-E open same story Q1096 won't get enough power.
Hopefully, Murphy will be kind... I'm off to bed.
I had a think about this apparent loss of voltage to Q1096. In addition to R1009 (which frustratingly is OK & you confirmed it is definitely physically connected through to C1105), there's a couple of other possibilities:
1. R1280 - a 5K6 resistor on Q1096's collector, could you check if it's open circuit? If it's open, Q1096 won't get power & it also won't turn on Q1009.
2. Q1009 - check for the base - emitter diode (& might as well check for base - collector diode). If B-E open same story Q1096 won't get enough power.
The previous post is one solution to frustration (with a Class D O/P stage?), I hope we can find a less brutal option...
When amplifiers like this have offsets on all channels it's wise to check the output of all of the voltage regulators, especially the +/- 12V or 15V ones.
The other thing that will do this is wire links or PCB traces that have corroded out, sometimes causing the ground reference for the amplifier section to be lost.
A grossly unbalanced supply (or missing rail / ground) can tilt everything and make it look like multiple channels are faulty.
I've got different priorities today, it's my wife's birthday i.e. happy wife, happy life.
Fig 6 (page 20) shows how to disassemble the amplifier but keep all the interconnects. Maybe the rear panel has been removed to gain access to access to main(3) & the other boards.
There's some text as well:
When checking the P.C.B.:
• Put the rubber sheet and the cloth over this unit.
Follow the procedure below to place the amp unit.
(Fig. 6)
• Connect the ground points of the heatsink and subchassis
unit to the chassis with a ground lead or the
like. (Fig. 6)
• When connecting the flexible flat cable, be careful
with polarity.
• Reconnect all cables (connectors) that have been
disconnected.
When amplifiers like this have offsets on all channels it's wise to check the output of all of the voltage regulators, especially the +/- 12V or 15V ones.
The other thing that will do this is wire links or PCB traces that have corroded out, sometimes causing the ground reference for the amplifier section to be lost.
A grossly unbalanced supply (or missing rail / ground) can tilt everything and make it look like multiple channels are faulty.
Something else to keep in mind is that hi-fi amplifiers sometimes use the chassis as the common return (0V) for various signal paths.
You can often spot the important 0V points, such as a metal tab on the RCA sockets, a threaded PCB mounting tab, etc.
If you try and run the unit partly disassembled or with out all of those grounding screws back in place things can get wacky.
1. The DC offset is definitely really there. There is a thick wire running to each output channel on MAIN(1/2) from MAIN(3), these are wires I cannot disconnect (they are crimped at both ends to either board) and joked early on about splicing spade connectors into. The offset of about -6.5v is present on all of them except the black one, which is the ground reference for the board. Schematic indicates that all of these should be 0.0v.Are these wires the channel outputs (before the protection/muting relays)?
2. MAIN(2) has a small 3 pin connector labeled W1003 that has I_PRT_R, -LB_R, and +LB_R. These are supposed to be +55.6v, -53.8v, and +55.7v respectively. The values I get when checking are +57.4, -6.85, and -1.87.-LB_R,+LB_R (& -LB_L,+LB_L) are power rails to the power amp driver & as noted, they are completely out of spec e.g. -6.85V in lieu of -53.8V, -1.87V in lieu of +55.7V.
1. The DC offset is definitely really there. There is a thick wire running to each output channel on MAIN(1/2) from MAIN(3), these are wires I cannot disconnect (they are crimped at both ends to either board) and joked early on about splicing spade connectors into. The offset of about -6.5v is present on all of them except the black one, which is the ground reference for the board. Schematic indicates that all of these should be 0.0v.Are these wires the channel outputs (before the protection/muting relays)?
2. MAIN(2) has a small 3 pin connector labeled W1003 that has I_PRT_R, -LB_R, and +LB_R. These are supposed to be +55.6v, -53.8v, and +55.7v respectively. The values I get when checking are +57.4, -6.85, and -1.87.-LB_R,+LB_R (& -LB_L,+LB_L) are power rails to the power amp driver & as noted, they are completely out of spec e.g. -6.85V in lieu of -53.8V, -1.87V in lieu of +55.7V.
With the driver having such out of wack power supply rails, the channel power amplifiers won't be working in any sort of linear operating region.
The DC offset of -6.5V on the channel outputs (assumed from above) is more likely fortuitous voltage getting to the base of the output darlington transistors (which do have the proper supply voltages on their collectors).
-LB_R,+LB_R (& -LB_L,+LB_L) come from the +LB, -LB regulators Q1009, Q1010, Q1096 etc on Main(3). Do you now have better access to this area for a revisit/probing?
If so, could you do a voltage measurement of Q1096's collector? Could you also measure the voltage on Q1009's collector? (see attachment)
I've been harping on a bit (sorry) but there's something really fishy going on i.e. these regulators are turned off/faulty for some reason.
| Base | Emitter | Collector | |
| Q1009 | 57.6v | -1.92v | 57.6v |
| Q1096 | -0.25v | -0.13v | 57.6v |
| Q1097 | --- | -0.13v | -1.92v |
| Base | Emitter | Collector | |
| Q1009 | 57.5v | 0.0v | 59.95v |
| Q1096 | 3.3v* | 1.9v | 57.0v |
If the output of the bad channel is exactly the same as one of the main voltage rails, it will be a shorted output transistor. In that case I'd replaced both the NPN and PNP pair as well as the driver transistors and bias transistor. Also check all resistors around those transistors.
Q1087N & P -- STD01N & P -- Transistor pair
Q1088 -- 2SC3906K T146 R,S -- Transistor pair
Q1089 -- KTA1517S GR TP -- Transistor
Q1091 -- 2SA1208S/T-AE -- Transistor
Q1092 -- HN4C06J -- IC
Q1093 -- 2SC2910S/T-AE -- TransistorThe output transistors are Darlingtons. From the datasheet, they have internal pulldown resistors (see attachment). This may cause the transistor to appear to be "leaking" when diode testing the E-C (in one direction). I tested a known good Darlington (with pulldown resistors) but a different type to the STD01N/STD01P used in this amplifier & it showed up as being leaky.
It might be prudent to diode test another channel's output transistors (with no DC offset), just in case...
My Darlington transistor measured about 9Kohm (E-C). If it's a dead short, that's different i.e. it's stuffed.
Collector-Emitter drop: 0.6v.
Emitter-Collector drop: 0.5v.
Base-Collector drop: 0.66v.
Collector-Base drop: 1.5v.
Base-Emitter drop: Open circuit.
Base-Emitter resistance: Open circuit.
Cathode-Base drop: 1.3vCollector-Emitter: 3.5M
Emitter-Collector: 5M
Base-Emitter: Difference here. 8M on the good channel, 14M on the bad one.
Emitter-Base: Difference here too. 4.5M on the good channel, 1.7M on the bad one.
Base-Collector: Difference here too. 5M on the good channel, 10M on the bad one.
Collector-Base: 5M on both.
If Q1091 couldn't turn on, the output transistors' bases would be pulled towards -LB-L (-53.8V) by constant current sinks Q1105, Q1093 i.e. creating the symptoms you've got. Have you checked Q1105 - it might have caused Q1091 to fail?
Fingers crossed...
I had another look at circuit. Maybe check D1080, D1081 as well. They set the voltage on the bases of Q1105, Q1093, Q1095 and their constant current sink value e.g. Q1105 would sink about 2.7mA (0.6V/220ohm). Normally it should be 2 diode drops off -LB_L. If one of the diodes went open, then the current sink would have a much higher current (e.g. possibly frying Q1091).
I had another look at circuit. Maybe check D1080, D1081 as well. They set the voltage on the bases of Q1105, Q1093, Q1095 and their constant current sink value e.g. Q1105 would sink about 2.7mA (0.6V/220ohm). Normally it should be 2 diode drops off -LB_L. If one of the diodes went open, then the current sink would have a much higher current (e.g. possibly frying Q1091).
FYI, Q1105 and D1081 test out OK, but with the parts in place I can't determine if it's actually Q1091 or Q1088 as the test path for Q1091-BC and Q1088-CE is the same, so I'll remove Q1091 later today and test it in isolation and Q1088 without Q1091 interfering.
FYI, Q1105 and D1081 test out OKI'm being a bit pedantic, did that test also include D1080?
Maybe check D1080, D1081 as well.
FYI, Q1105 and D1081 test out OKI'm being a bit pedantic, did that test also include D1080?Maybe check D1080, D1081 as well.