2250B Questions
- Thread starter jc7070
- Start date
Steven Tate
CEO Flat Forehead Soc.
I use Therm O Web Super Tape in 1/8" width from Amazon. It is basically tape glue on an orange plastic backing that peels off, acting like double sided tape. Remove any small screws holding the dial onto the chassis, carefully peel the plastic dial face away from the chassis, remove discolored velum, clean off the glue with isopropyl alcohol (not that easy). Place new Super Tape around edges, peel off orange backing, place new velum (48# velum, also on Amazon), more Super Tape as needed on the velum and replace dial face. There are other methods and materials, but this works for me. While you have the dial face off, replace the fuse bulbs - with LED's if you like. And if you want to replace the input indicator, stereo lamp bulbs and meter bulbs, this is the time to do it. Good luck!
Steve
Steve
The idea of double sided tape sounds a good way to do the job as I don't feel so comfortable to work with silicone or similar. A clean solution.
Just thinking about if the excess of that silicone or similar drips to the dial face, it wouldn't look good anymore.
I have an idea of using carpet knife to remove the dial face, that could work?
Anyway I will do this after I finish recapping rest of the boards.
Is it a feature or fault that when I turn off the unit I hear a pop occasionally, but not each time from the speakers?
I have tried to deoxit the power switch from both sides, maybe I should disassemble the whole switch, if it can be done. It's different construction than rest of the push buttons.
Both units make that sound on power off.
Just thinking about if the excess of that silicone or similar drips to the dial face, it wouldn't look good anymore.
I have an idea of using carpet knife to remove the dial face, that could work?
Anyway I will do this after I finish recapping rest of the boards.
Is it a feature or fault that when I turn off the unit I hear a pop occasionally, but not each time from the speakers?
I have tried to deoxit the power switch from both sides, maybe I should disassemble the whole switch, if it can be done. It's different construction than rest of the push buttons.
Both units make that sound on power off.
Steven Tate
CEO Flat Forehead Soc.
The unit probably has a snubber in the form of a cap+resistor either on the power switch or at the rear where power comes in. It's G001 on the schematic. The purpose is to eliminate this pop, and they lose their ability to do that over time. You can make your own with the proper cap and resistor or there are a couple of companies still making them in a single component. Of ourse, the other possibility is that the switch has badly corroded contacts and is just making more spark than the cap can handle. There is a modern equivalent switch available.
As for removing the dial plate, I use a single edged razor blade to tease it away from the chassis. Usually the old glue has hardened and is not that hard to remove. But be careful. You don't want to have to go looking for a replacement.
As for removing the dial plate, I use a single edged razor blade to tease it away from the chassis. Usually the old glue has hardened and is not that hard to remove. But be careful. You don't want to have to go looking for a replacement.
I see G001 on the wiring diagram, but there's no value to it. I suspect it's the ceramic cap .01uf located near the two main caps, but can't be sure at this point. I have two new 10000pf 450V ceramics with me, so I could replace that.
I did the power supply and equalizer boards on past two days, now they're good with new caps.
Testing the amp again I found this particular unit made funny *rapid popping sound* -sequence, just before stereo tuned into station unlike the other 2250B, which don't have FM issues.
I decided to take a look at what kind of a project would be P300 FM MPX board recap, but it proved challenging. Begins with the cover screws jammed in place. So I finally got them all loose. Browsing through few topics here on AK, they all recommended not to remove the wires from the P300 posts so I didn't. Popped the dolby board loose, it gave that much slack I was able to turn the board up just enough to replace two caps. C327 and C328, which both are 220uF. Looks like I must remove few wires, if I want to recap the rest of the board. I guess there's no other way, there's no room to work on it. Anyway it all was worth it, since now the rapid popping sounds are gone. The ones I pulled out measured for 278uf and 313uf, so they were way off spec.
While working on this board one of these brackets (picture) dropped off from somewhere.
Any clue where it comes from? The other one dropped off earlier.
I did the power supply and equalizer boards on past two days, now they're good with new caps.
Testing the amp again I found this particular unit made funny *rapid popping sound* -sequence, just before stereo tuned into station unlike the other 2250B, which don't have FM issues.
I decided to take a look at what kind of a project would be P300 FM MPX board recap, but it proved challenging. Begins with the cover screws jammed in place. So I finally got them all loose. Browsing through few topics here on AK, they all recommended not to remove the wires from the P300 posts so I didn't. Popped the dolby board loose, it gave that much slack I was able to turn the board up just enough to replace two caps. C327 and C328, which both are 220uF. Looks like I must remove few wires, if I want to recap the rest of the board. I guess there's no other way, there's no room to work on it. Anyway it all was worth it, since now the rapid popping sounds are gone. The ones I pulled out measured for 278uf and 313uf, so they were way off spec.
While working on this board one of these brackets (picture) dropped off from somewhere.
Any clue where it comes from? The other one dropped off earlier.
Attachments
Steven Tate
CEO Flat Forehead Soc.
The snubber is a combo part with something like a .1uF cap and 120 ohm resistor in one component. It looks like this picture - sometimes blue and sometimes brown or orange. And here is a thread where a modern equivalent has been discussed. See the top post.
http://audiokarma.org/forums/index.php?threads/2325-power-switch.785300/page-2#post-10815109
http://audiokarma.org/forums/index.php?threads/2325-power-switch.785300/page-2#post-10815109
Thanks. I looked carefully around the power switch and along the power line, but can't find that. Is it possible it was built inside the switch?
I have worked on several amps in the past and say Sansui AU 4900 has that part installed for example. Maybe I could check my other 2250B for that part, if it exists.
Anyway meanwhile looking for that snubber I discovered that those brackets in the picture belong to the preamp PE01 between the support stands and board
One thing leads to another. Also this search proved useful.
I have worked on several amps in the past and say Sansui AU 4900 has that part installed for example. Maybe I could check my other 2250B for that part, if it exists.
Anyway meanwhile looking for that snubber I discovered that those brackets in the picture belong to the preamp PE01 between the support stands and board
One thing leads to another. Also this search proved useful.
Steven Tate
CEO Flat Forehead Soc.
I've never seen one built into a switch. The ones I have seen were either on the switch (like the photo) or inside the back of the chassis on one of the A/C outlets.
Coming back to this. There's no snubber present at the power switch or the rear panel AC outlets. It always remains a possibility that somebody removed them. I didn't check my other receiver for that yet, because it's the daily driver
Yesterday I had time to recap the FM multiplex board P300. It was a sort of challenge, but it was definitely worth it. Removing 4 posts (I think these were J307, J310, J302 and J317) gave enough play to lift the board up high enough to access the solder points.
Basically all of the caps were drifted ~ 40% off the spec and similar fashion drifts found at P200 board.
Also removed the dial plate. Vellum is discoloured as expected. Been working on removing the paper bits and glue from the plate edges. It's pretty good now, but some stickiness remain yet. I have used only water, soap and fingernails so far.
Placed order on set of new cool white LEDs among double-sided tape and I'm waiting them to be delivered on next week.
Meanwhile I should decide if I want to use leds or just regulars for indicator lamps. However I stumbled upon some posts saying at least certain type of leds for stereo lamp needs a resistor not to cause damage to the chip behind the lamp.
So my local supplier have regular lamps 10V 40ma Bi-pins, 8V 60ma for dial pointer and 14V 40ma (stereo) in stock. I wonder if these would be suitable and if they're bright enough?
Also leds would be alright for me, but it's essential to know what kind of leds can be installed without risking the chip.
Yesterday I had time to recap the FM multiplex board P300. It was a sort of challenge, but it was definitely worth it. Removing 4 posts (I think these were J307, J310, J302 and J317) gave enough play to lift the board up high enough to access the solder points.
Basically all of the caps were drifted ~ 40% off the spec and similar fashion drifts found at P200 board.
Also removed the dial plate. Vellum is discoloured as expected. Been working on removing the paper bits and glue from the plate edges. It's pretty good now, but some stickiness remain yet. I have used only water, soap and fingernails so far.
Placed order on set of new cool white LEDs among double-sided tape and I'm waiting them to be delivered on next week.
Meanwhile I should decide if I want to use leds or just regulars for indicator lamps. However I stumbled upon some posts saying at least certain type of leds for stereo lamp needs a resistor not to cause damage to the chip behind the lamp.
So my local supplier have regular lamps 10V 40ma Bi-pins, 8V 60ma for dial pointer and 14V 40ma (stereo) in stock. I wonder if these would be suitable and if they're bright enough?
Also leds would be alright for me, but it's essential to know what kind of leds can be installed without risking the chip.
Alrighty, I have proceeded with LEDs.
It's looking great so far.
I ran into a minor problem with the stereo indicator lamp.
Althrough stereo indicator lamp works exactly the way it should on FM mode, the problem is that the Stereo LED stays illuminated regardless of the function selected.
First tried with LED + 1.8k resistor, then with 2.2k resistor. Problem persists.
I measured the voltage at the JY15 terminal (goes to one of the stereo pins) and reading there 13.56 vdc. Same voltage is applied to JY15 with all functions.
Tested the other 2250B and JY15 is fed with 13.00 vdc regardless of the function.
I wonder if it's the LED itself? According to this particular red led's "turn-on threshold voltage is a minimum 2V".
I need a LED with different specification?
It's looking great so far.
I ran into a minor problem with the stereo indicator lamp.
Althrough stereo indicator lamp works exactly the way it should on FM mode, the problem is that the Stereo LED stays illuminated regardless of the function selected.
First tried with LED + 1.8k resistor, then with 2.2k resistor. Problem persists.
I measured the voltage at the JY15 terminal (goes to one of the stereo pins) and reading there 13.56 vdc. Same voltage is applied to JY15 with all functions.
Tested the other 2250B and JY15 is fed with 13.00 vdc regardless of the function.
I wonder if it's the LED itself? According to this particular red led's "turn-on threshold voltage is a minimum 2V".
I need a LED with different specification?
Last edited:
Steven Tate
CEO Flat Forehead Soc.
The stereo LED is always on in phono, tape and aux modes. The reason is, they are always stereo inputs. It's normal operation.
Oh yea 
actually I had a break, eating and did some other stuff for a while. Realized this could be it and I didn't try mono switch.
Really should make breaks once in a while.
I've been working on Sansui's too long. For example the lamp on Sansui 5000 is "FM Stereo" and it's lit only on FM mode obviously.
Many other receivers also have Stereo go out on other inputs.
Then read some posts on the forum about different resistor sizes for the LEDs that caused some problems...
So when I saw this lamp lit on other modes, I thought it must be a malfunction.
....poor me and destroyed a stereo lamp pcb track for this ordeal
well it can be fixed
actually I had a break, eating and did some other stuff for a while. Realized this could be it and I didn't try mono switch.Really should make breaks once in a while.
I've been working on Sansui's too long. For example the lamp on Sansui 5000 is "FM Stereo" and it's lit only on FM mode obviously.
Many other receivers also have Stereo go out on other inputs.
Then read some posts on the forum about different resistor sizes for the LEDs that caused some problems...
So when I saw this lamp lit on other modes, I thought it must be a malfunction.
....poor me and destroyed a stereo lamp pcb track for this ordeal
well it can be fixedSteven, Tom, Goat, thanks for your kind assistance.
Thanks to Audiokarma users, it was a great help to restore this piece.
Now I have assembled the receiver back to daily service.
Took some photos along the way, so why not to put them here as well.
pe01 before/after
p800 before/after
p300 before
p300 after
p700 right after
Signal strength / FM Tuning meters refurb
Signal strength / FM Tuning meters refurb
2250B twins
2250B at night
2250B goes back to service
It looks better in real.... and sound is of course fabulous!
A/B testing these brought more life to low freq to the freshly restored receiver.
It's louder and FM stage is more detailed.
What else can I say, caps are still burning in.
Thanks to Audiokarma users, it was a great help to restore this piece.
Now I have assembled the receiver back to daily service.
Took some photos along the way, so why not to put them here as well.
pe01 before/after
p800 before/after
p300 before
p300 after
p700 right after
Signal strength / FM Tuning meters refurb
Signal strength / FM Tuning meters refurb
2250B twins
2250B at night
2250B goes back to service
It looks better in real.... and sound is of course fabulous!
A/B testing these brought more life to low freq to the freshly restored receiver.
It's louder and FM stage is more detailed.
What else can I say, caps are still burning in.
Steven Tate
CEO Flat Forehead Soc.
Great looking work! It's very satisfying to bring one of these beautiful units back to optimum health. 
