Yes, that's right, they are the exact opposite of an RB152 pinout which is ~ - + ~ all the new PCB mounting bridge rectifiers I looked at were + ~ ~ - pinout.
Help on an sansui x1
- Thread starter w_barton
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w_barton
Active Member
I actually was measuring Pin 46,48, and pin 43 and 45. There was no voltage and today I did an deep dive into F-2778 board to find find out what the issue was with the ground. What i found was that Sansui uses the F-2772 MC,MM mother circuit ground to complete the path to ground for the -10 volts via the cables from the F-2778. If the cables are not connected, you will have no ground for the -10v. After connecting the respective pins to their post. My -10 came right up.
The voltage here in Vietnam (220V) are not very stable and like you mentioned is much higher then 220, from your explanation, of 67 to 90v. That is what I am experiencing. I normally run a line regulator thats feeds my isolation transformer on my system, but only run an isolation transformer on my work bench and puts out much higher then the expected nominal 100v. (105-110)
w_barton
Active Member
hi, you are right about the pinouts on the rb 152. I was surprised that they would designed into that pin configuration. I uses a BR64. It is made so that I could rearrange the pins to match the rb152. Looks like the leaning tower of pisa, but it works.
w_barton
Active Member
you are right, what I meant to say that the 90 volts was present on the output of the respective bridges dealing with the -47 volts, Pins 53 and 52. The above mentioned pins were for the missing voltages that I resolved by reconnecting the cables at phono/ mother board( F-2772_
w_barton
Active Member
and I had to use a BR64 to be able to use it in that configuration. Not the prettiest, but it works
GrisPato
Super Member
Ah, thanks for clearing that up. That would be still around 25-30% higher what would mean around 260 VAC line voltage. Really crazy, could not imagine that.
So if I understand it well, you resolved the problem for your phono boards powersupply with the ground pins?
If so, happy listening again!
Is amazing how open circuit can change the voltages!
w_barton
Active Member
The voltage here in Vietnam is not very stable or precise. I bought a voltage regulator locally and the supposedly 220 regulated output is at times 8 volts higher. We have brownouts and power shutoffs. I have to use an isolation transformer to avoid getting shock. I had several incidents recently where I be measuring resistance and i accidently touch B plus and I get a massive cap discharge. It seems some of my caps are not discharging to ground. I wonder the reason they retain a charge is the ground is missing ?
w_barton
Active Member
Thanks G, this was a miller lite moment. But I still have an arcing problems with the caps, as if the grounds were missing. they retain their charge and they do a might fine light show when accidently touched. I having issues with my right channel MM board. It keeps wanting to burn out the R04 and R02 resistors of the F-2778 board. But for now, I think would replace the fuse resistors and the VD1212 and MV 12 diodes.
GrisPato
Super Member
Is it possible to measure the voltage drop over them?
Look for a short circuit on the output, pins 8 - 12 (+47V) and 12 - 16 (-47V). Otherwise remove and test C04 & C02, and if good remove TR06 & TR08 (the 'pass' transistors), and see if that stops the burning.
w_barton
Active Member
Thank you Hyperion! I live in a small city and they only have one electronic hardware store. For the most part the store itself carries only cheap Chinese parts and its inventory selection is very small. An alternative will be shopee.vn. But hardware store most of the products they sell originates from China and ship to Vietnam. It normally take about 14 days to receive the goods from China. I do most of my shopping from Mouser. This is one project that I would call the project from hell...Look for a short circuit on the output, pins 8 - 12 (+47V) and 12 - 16 (-47V). Otherwise remove and test C04 & C02, and if good remove TR06 & TR08 (the 'pass' transistors), and see if that stops the burning.
. I will do what you suggest tomorrow and then get back to you with my discovery. Thanks again Hyperion for all the great support !
w_barton
Active Member
the problem seem to manifest it self between the outputs of the two respective bridges and the power supply board. Everything before the bridges (AC line is normal) is as it should be. I will attempt to implement your suggestions and I will get back to you with my findings. Thank you again friends for your time and valuable experiences!
GrisPato
Super Member
So I understand it well that this high voltage measurement was solved by connecting grounds?
This to?
So where we are now is normal VAC around +52/-52. Pin 9-11,49-51
DC voltages after bridge rectifiers are . .? wrong? Pin 58-60-62, 52-54-56.
DC voltages after regulation are . . .?
Pin 7-11-9, 8-10-12.
I think Hyperion advise is sound. More current pulled by the pass transistor will mean more current through the resistors. I just have the feeling the cause is upstream.
w_barton
Active Member
Hello everybody, sorry for the delay in responding. I was pretty busy and did not have time to really work with my toy. I finally had the chance snoop around and after a side trip of my toy not turning on (Cold solder joint on the load resistor R621). Started to work on Hyperion idea and did a quick check on unloading connectors, 52,53,54 and 58,59,60. Measured male pins of the respective pins and wala...the 67 volt supplies were present! but when I reinstalled the connectors, it went up to 90 volts. I decided to unsolder R04 and R02 on the input of the power supply to isolate it. from the power supply of the protection circuit board. Instead getting the 67 volts, my 90 volts was still hanging around. That eliminated the power supply board. I again when back to the schematic and noticed that there were two other output lines around in parallel with the outputs to the power supply board. The 67 volts provides Vcc and -VCC for the left and right drivers. I then unload the connection feeding the drivers. (Note: my right channel driver board is out due to some parts needing replacement). The reading were still reading in the 90's. I had unload every thing associated with the 67 volt supply, but was still was indicating 97. The only active device are Cap 713,714. Which are the dual caps. I measure them and both read good. But, the ground was missing from one of the caps due to the missing driver amp. So, I don't know if that reason of the increase voltage.
GrisPato
Super Member
Know that situation .
Was reading a thread from Bumpalump, a professional audio equipment restorer from Poland. He finished restoring a G7700 that came to him in really bad condition in two days, and I am assuming with a lot of hours a day. I was really jealous, would love to just be able to lock myself up and work 2 full days on my amplifier!
Never going to happen. .
No ground on one or both of the capacitors for sure can create that voltage. Had the same with an AU 719 I restored last year. So as long as you have the board out you can ignore that. Unless you need to do measurements downstream of that. Than you will have to provide the ground otherwise the measurements will be meaningless.
w_barton
Active Member
Thank you GrisPato for the affirmation! I receive great joy when I can find the culprit . I use to work as a test tech for a manufacturing company and it helped me hone my troubleshooting skills, and, friends like you and Hyperion further expand my knowledge. Thank you so much guys for the time and effort you have involved into my problem!
The ground design of my toy was really bad. Instead of short ground points, they run the grounds points between boards via wire harness. So that removing a board or a connector would upset the apple cart and cause caps not being discharged and the tech experiencing a fire show when attempting to make measurements. I would like to tie both ground points of the caps to ground of the chassis for both a safety and protection for other circuits. and I suspect that the dual caps somehow like a battery and recharge the smaller caps, I noticed that they get recharged even after discharging it. What do you guys think?
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