Yamaha CR-600 restoration advice
- Thread starter Joolian
- Start date
AC or DC?
Should have at least 30 vdc on the common end of each of those resistors.
I apologize, I didn’t mean to somewhat abandon this thread, things got busy around the holidays and I had to wait for more solder and solder wick to arrive to keep working on things.
I discovered that I had botched the pinout on two new transistors that replaced TR705 and TR706 and had to order new ones as I’d already cut the legs and couldn’t switch them around. After replacing these correctly as well as making sure all transistors in the protection circuit were in correctly (oops..) things have somewhat improved or just moved laterally, depending on who you ask. Here’s the current readings:
55V on DBT (voltmeter on DBT was reading 0L before), bulb is definitely dimmer than it was. If it means anything, when powering up on DBT the bulb flashes twice and then settles out, I’m assuming this is just the filter caps filling though?
+15.3V AC across yellow transformer wires
~+15.15V on all ends of FR802 and FR803 except ~+14.6V on left side of FR803
+4.88V on +12 wire going from power supply to main amp
+5.30V on +12r wire going from power supply to main amp
Midpoint for VR701 is ~+1.3V but very very slowly dropping
Midpoint for VR702 is ~+11.7V, dropping similar to VR701
Idle on VR703 is +23mV stable
Idle on VR704 is showing no voltage at all
TR801 now +5.3V at base, +15V at collector, and +4.8V at emitter
TR802 now +13.2V at base, +14.4V at collector, and +12.6V at emitter
+BL and +BR on power supply both giving me +12V
-BL and -BR both giving me -12V
Thank you everyone for your help so far, I hope you all had wonderful holidays.
I discovered that I had botched the pinout on two new transistors that replaced TR705 and TR706 and had to order new ones as I’d already cut the legs and couldn’t switch them around. After replacing these correctly as well as making sure all transistors in the protection circuit were in correctly (oops..) things have somewhat improved or just moved laterally, depending on who you ask. Here’s the current readings:
55V on DBT (voltmeter on DBT was reading 0L before), bulb is definitely dimmer than it was. If it means anything, when powering up on DBT the bulb flashes twice and then settles out, I’m assuming this is just the filter caps filling though?
+15.3V AC across yellow transformer wires
~+15.15V on all ends of FR802 and FR803 except ~+14.6V on left side of FR803
+4.88V on +12 wire going from power supply to main amp
+5.30V on +12r wire going from power supply to main amp
Midpoint for VR701 is ~+1.3V but very very slowly dropping
Midpoint for VR702 is ~+11.7V, dropping similar to VR701
Idle on VR703 is +23mV stable
Idle on VR704 is showing no voltage at all
TR801 now +5.3V at base, +15V at collector, and +4.8V at emitter
TR802 now +13.2V at base, +14.4V at collector, and +12.6V at emitter
+BL and +BR on power supply both giving me +12V
-BL and -BR both giving me -12V
Thank you everyone for your help so far, I hope you all had wonderful holidays.
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@Joolian did you manage to get this resolved?
I have just successfully recapped the power supply board on my CR-600. I have not touched the main amp board yet as best to mess with one thing at a time if possible.
I have 14.68V across my yellow transformer wires (VI) with 124 VAC coming in so 15.3V sounds fine. Edit: I measured the across the purple wires which are labeled VI. Across the yellow wires (YE) I measure 36.12V AC so 15.3V is not fine. See below.
This goes through FR804 and then a bridge rectifier to create +12R which is not regulated. +12R measures 16.2V for me once settled after the relay clicks (all my incandescent lamps are dead).
Here are my other voltages:
+12 12.04V
+12M 11.54V
+30 29.52V
BL and BR are about + / - 38V (measure -BL, +BL, -BR, +BR separately with respect to ground)
If you look at the schematic (attached) the voltages for TR802 are labeled.
I have just successfully recapped the power supply board on my CR-600. I have not touched the main amp board yet as best to mess with one thing at a time if possible.
I have 14.68V across my yellow transformer wires (VI) with 124 VAC coming in so 15.3V sounds fine. Edit: I measured the across the purple wires which are labeled VI. Across the yellow wires (YE) I measure 36.12V AC so 15.3V is not fine. See below.
This goes through FR804 and then a bridge rectifier to create +12R which is not regulated. +12R measures 16.2V for me once settled after the relay clicks (all my incandescent lamps are dead).
Here are my other voltages:
+12 12.04V
+12M 11.54V
+30 29.52V
BL and BR are about + / - 38V (measure -BL, +BL, -BR, +BR separately with respect to ground)
If you look at the schematic (attached) the voltages for TR802 are labeled.
Attachments
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Sorry to get back to you so late, I haven't checked the site in a good while. I ended up just setting this one aside while I was doing other projects.
Just to clarify, are you getting 14.68VAC across the yellow wires (YE) or the purple wires (VI)? I see where VI goes into FR804 and to a bridge rectifier, although I'm only getting 6.2VAC across the purple VI wires. From my incredibly rough understanding of transformers and from looking at the schematic I have a feeling VI and YE are supposed to be giving me about the same voltage.
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My bad. The VI transformer wires are indeed purple and that is where I measured the 14.68V AC.
Across the yellow (YE) transformer wires I measure 36.12V AC.
Just to clarify you are measuring across both yellow wires when you get 15.3V AC and not from one yellow wire to ground?
Across the yellow (YE) transformer wires I measure 36.12V AC.
Just to clarify you are measuring across both yellow wires when you get 15.3V AC and not from one yellow wire to ground?
Yes, measuring across both wires. Seems strange that I'm getting ~1/2 the voltage I should be expecting from the transformer. According to my DBT it's pulling 55V in though.
Well that would explain it. I am getting 36.12V from 124V mains. At 55V I would be seeing 55 / (124 / 36.12) = 16V
I assume your bulb has a medium glow since it is taking more than half of the voltage? If so you need to get to the bottom of this first.
FYI with a healthy power supply on a 75W dim bulb I am seeing about 32V across the yellow wires.
I assume your bulb has a medium glow since it is taking more than half of the voltage? If so you need to get to the bottom of this first.
FYI with a healthy power supply on a 75W dim bulb I am seeing about 32V across the yellow wires.
Medium glow on a 60W bulb (highest I can find). It's not glowing nearly as bright as it was when I was working on my Kenwood KA-3500 and since it's actually giving me a voltage reading and not 0L I assumed the glow was a mix of using a 60W bulb for a higher power receiver, but I will do some poking around for a short.
There has to be an issue in the main amp board as for left channel bias I’m reading .235V and right channel is reading 0V, neither are adjustable. I was under the assumption that it was something in the power supply causing this as both channels are fluky but maybe not. Outputs are fine, but I’ll pull them again just so I can access the back of the main board.
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So with the equivalent of a 100W bulb the tuner is only seeing 62V. It is not time to come off the DBT yet...
Not sure what is up with your bias but even at a lower voltage your left channel is too high (should be 0.023 ±0.005V). Are you saying turning VR703 / VR704 has no effect?
Not sure what is up with your bias but even at a lower voltage your left channel is too high (should be 0.023 ±0.005V). Are you saying turning VR703 / VR704 has no effect?
All 4 pots for bias and offset have no effect from being turned. Considering I'm sitting at about half voltage from the DBT I think my power supply voltages look okay, so would I be correct in thinking that it's something towards the "front"/input of the main board since it's effecting both channels' bias and offset?
Only common circuitry is the power supply!
Have checked voltages (where labeled) for the power supply transistors and while they all check out fine relative to the DBT voltage, I will note that the emitter of TR802 started out around 4-5V and took a while to climb up to 14V. I didn’t notice this with any of the other transistors.
This needs attention. It is very likely your whole problem.
Possible casualties
TR802
TR804
D806 -- 31v Zener *
C814 -816 *
R806,807 & 809
The dim bulb exaggerates the issue.
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Needs to be a stable 30v DC. This is the power supply for the pre-amp and EQ circuits.
How would I go about testing a zener with a DMM?