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Post by serafis on Oct 6, 2024 16:10:40 GMT -5
See Post #4 onwards I've been given a Pioneer SC-LX57 which looks like it's been dropped and then left out in the rain - quite a few dents, broken mains voltage selector, and a fair bit of corrosion on the chassis and some PCBs. Service manual is at elektrotanya.com/pioneer_sc-75_sc-1528_sc-1523-k_sc-lx57_sm.pdf/download.htm although it only has schematics and board layouts, no diagnostic help. I've cleaned it up as far as possible and bypassed the voltage selector, and it now powers on fine, but with no sound on digital inputs, only on analog inputs and only in Pure Direct mode. The firmware version displays as 1-149020516108, which AFAIK (from another model's manual) means as follows: 1 = Big Version number of Main com 149 = Small version number of Main com 020 = Version number of Sub com 516 = Version number of DSP 108 = Version number of BridgeCo I've also read the DSP EEPROMs (IC9004 and IC9704 on the HDMI board) using a CH431 programmer, and they both look OK as far as I can tell. I tried a USB firmware upgrade anyway, but after 50% it said No Update Necessary. I suspect one or both DSP chips is bad, even though the firmware seems OK. Given the sorry state of this receiver, I don't think it's worth trying to replace them, but would appreciate any other ideas or diagnostic tips. TIA, Jon. |
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Post by mastertech on Oct 6, 2024 17:46:05 GMT -5
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Post by serafis on Oct 6, 2024 19:56:07 GMT -5
Thanks, yes that did help although parts of it seemed to be missing letters in my PDF reader, which made it a bit hard to follow. Anyway, traced some of the digital signals between the HDMI board and the DAC board with the scope, and found some signals missing. Removed the HDMI board and the DAC board for inspection again, checked the bridge board connectors, couldn't see anything obvious, put it back together and now have analog sound on all sound fields (haven't checked digital yet).
So what had changed? Nothing, except removing and replacing the two boards. So after a bit more investigation, determined that the issue was with one of the ground connections from a bracket on the DAC board to the chassis via a screw on the back panel, which apparently wasn't making good connection due to corrosion. Remove that screw and the sound stops, put it back in and the sound comes back.
Anyway, I'll clean it all up a bit more and test digital audi, HDMI audio and video, and report back... but I'm hopeful now!
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Post by serafis on Oct 7, 2024 3:59:20 GMT -5
Well, all audio functions are now working as they should. However, two more issues have since surfaced. I have around 0.5V DC on the left surround channel, not sure where that's coming from so more investigation needed. And the Setup Mendu displayed thru HDMI glitches momentarily and irregularly, although when watching a video there doesn't seem to be a problem. I think I'll re-check power supplies and capacitors for ripple / noise. But great progress so far.
And I now have the DSP EEPROM .bin files if anyone needs them!
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Post by mastertech on Oct 7, 2024 9:13:40 GMT -5
Good to hear. Keep at it, you'll find it.
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Post by serafis on Oct 8, 2024 20:56:04 GMT -5
Good to hear. Keep at it, you'll find it. Not sure I will  Here's what I've found so far. There's around -600mV DC on SL channel and around -18mV DC on SR channel. Other channels are less than 4mV DC. Interestingly, SL, SR, SBL and SBR are all phase-reversed on input and output, presumably to minimise supply 'bus pumping' that can be a problem with class-D amps. I removed the bridge between AUDIO ASSY and IR BUFFER_S ASSY, which provides the only inputs to IR BUFFER_S ASSY, in case the DC was coming from AUDIO ASSY, but no difference. Hence I think the issue must be on either IR BUFFER_S ASSY (p68-69) or D-AMP_S ASSY (p78-79). I removed the boards and tested all component values that I can read with the DMM on both boards against a good channel and found no differences. Cleaned bit more corrosion off too. I reassembled, leaving out the HDMI, DAC, AUDIO, COMPONENT, COMPOSITE and POWER boards, and the top shield plate of the D_AMP board so I could get at it in situ, and leaving its various regulated power connections in place (CN4004, CN4003, CN4002 and CN4001, p146). I then directly powered the main transformer, and checked that each connector had the correct voltages. But for some reason, with the D_AMP board powered in this way, I just get around -1.8V DC on all channel outputs, so there's clearly something else I'd need to do to get the D_AMP board running properly in this configuration. Maybe something to do with CN4000 which comes from the HDMI board and may carry signals that tell the D_AMP to run properly. Anyway, now I'm stuck - don't know what to do next. Any ideas? |
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Post by serafis on Oct 9, 2024 15:18:30 GMT -5
I reassembled without the IR_BUFFER_ASSY board, so the D_AMP ASSY board has no audio inputs, only the various voltages and control signals from the HDMI board. Now the SL channel has +2.8VDC and the SR channel has +0.7VDC (the other channels have negligible DC), so the issue is definitely with the D_AMP_ASSY board.
Looking at the schematics (P78-79), I was thinking the problem might be the IRS2092SPBF PWM driver (IC4301/4401) or the IRF6775MPBF-TRB output MOSFETs (Q4301/4302/4401/4402) - these are tiny SMD MOSFETs and so quite difficult to remove / test / replace. But I managed to replace them on the SL channel anyway with some that luckily I had in the parts bin from a previous project. Unfortunately no difference.
Any ideas as to where to look next?
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madmal
Junior Member
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Post by madmal on Oct 10, 2024 13:04:14 GMT -5
You're a brave man taking on a project that's been left in the rain.
Can you swap pwm drivers between channels to eleminate those?
The amps on these Pioneers is usually solid and luckily have never had to fix them.
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Post by serafis on Oct 12, 2024 23:28:52 GMT -5
Yes, it was in a very sorry state when I got it. I was surprised at how far I've managed to get with this one.
I'd already installed a new PWM driver along with the MOSFETs, unfortunately no difference.
I made a jig to test the SMD transistors in situ with my transistor tester and there is no significant difference in Vf or hFe between any of the transistors in the bad channel(s) and good channel(s), or when measured with a DMM in diode mode. All other components that I can test also read the same between channels. I've replaced the electrolytics in the pre-MOSFET stage too, no difference.
The only difference I can find is that when I put an ohmmeter across C4305 (SMD, 1000pF) and the same capacitor in the other channels, in all channels except the bad one it immediately reads around 5.95M. On the bad channel, it starts at around 5.7M and then goes up over a few seconds to 5.95M (almost as if a capacitor is charging somewhere). But for the life of me, from the schematics, I can't see what could possibly be causing this, or even if this is what is causing the DC problem (and why).
I'm almost ready to give up on this one and chuck it in the bin, so any help or insights much appreciated.
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Post by serafis on Oct 13, 2024 20:47:41 GMT -5
Ok I give up on this one. I've spent more than enough time on it - it just doesn't want to be fixed. So I'll salvage some bits for the parts bin, and trash the rest.
Onto the next project, for NZ$20 picking up an Integra DTR-30.4 tomorrow that won't turn on, plus a Cambridge Audio DVD player that won't read discs. Hopefully easier fixes than this one!
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Post by mastertech on Oct 13, 2024 21:24:44 GMT -5
You could always pull the amp module, add some jumper wires and make it a nice Pre Pro. Been there.
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madmal
Junior Member
Posts: 22
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Post by madmal on Oct 17, 2024 3:45:37 GMT -5
Ok I give up on this one. I've spent more than enough time on it - it just doesn't want to be fixed. So I'll salvage some bits for the parts bin, and trash the rest. Onto the next project, for NZ$20 picking up an Integra DTR-30.4 tomorrow that won't turn on, plus a Cambridge Audio DVD player that won't read discs. Hopefully easier fixes than this one! Would be interested in the digital board if you;re scrapping it.... I think these use the D808K013DPTP4 version of the DSP ? |
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Here's what I've found so far.
