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Hi, I have Cyrus 3 with a bad transformer (draws current when plugged in alone,but still works). It is dual secondary 29-0-29 and 7-0. Obviously I won't be able to find that, so I am thinking 2 transformers. I could find 30-0-30 160VA for the main. The 7-0 feeds power supply for the...

Hi, I got Yamaha A-S700 to fix. The guy that brought it said it turned on no sound. No it does not turn on at all. It does say in the manual if protection is on 3x the power will not turn on. There is a protection circuit with IC. There are instructions on how to disable it or reset it in the...

Hi, thank you all for advice. In the end I left the pre-drivers and drivers original - they were fine and matched too. I replaced what was wrong and the rest of small transistors. Bias was easy to set, so was offset. Here is a list of what I used in case somebody finds that helpful

And were you able to gain match them?

Sorry to bother again. DO you know what diodes are used for the flybacks? One of them is gone. Can I use 1n4004s?

Have any of you here used MJE15030/15031 for the drivers? I have their slightly lower voltage versions 15028/15029. I have like 8 of each and used them in the past where 15030/31 were replacements with no issue. But because here the gain matching matters - I am getting hFE of the NPN = 95 (6 out...

I found this, it should work there: https://ie.farnell.com/on-semiconductor/bc516-d27z/transistor-bipol-pnp-30v-to-226aa/dp/2453784

Hi, I have a question about Q503 on model 250m. One channel is gone and the other has the mpsa65 which is darlington transistor with gain of 45k hFE (measured). I see people use just regular BC556/557 instead. As above. Am I ok to do that too?

Can I ask you one more thing? Q503 is gone on the bad board (right channel) The left channel has the MPSA65 darlington transistor (hFE 45k when tested). On the below thread, it is saying a regular BJT is used on the moded PCB, but min has the darlington. Do you know if I should use some...

Great, thanks for confirming. Makes it easier if I know it was meant to be like this.

Hi, I got Marantz Model 250M to repair. It blows fuses (I was told). So I took it apart, checked the outputs and right channel has 3 out of 4 outputs bad. Also Q521 is gone and the pair of 0.1 5W collector resistors and one for the 0.15 Ohm resistors. Pre-drivers, and drivers are ok,also have...

Hi, sorry to revive this old thread. Could you please tell me how the two balance pots measure in center position? My balance was gone so I replaced the two pots closer to the case - 5k with pair of 2.2k resistors each and the second sets of pots - 3k with pair of 1.5k resistors each. Now it...

Hi, I have this amp and it works well. But when using the bulb test limiter with 150 watt bulb it lights up a lot. I have had similar powered amp (Technics su-v8) and it would just have low light after start up. There is no bias adjustment so it is probably ok as the amp works and the rated...

Don't stop your Floyd. I got it. The resistor has so many turns I was just away from the 'zone where the bias was measurable. I dialed it down to around 200 ohms (which took a lot of turns:-) and got some reading and was able to adjust from there then. The emitter resistors are 0.22 - red red...

Hi, thanks. If you have a chance could you measure what resistance you have now set betwen pin 1 and R6? (accros the variable resistor. Thanks

Have you been able to set the bias on the SU-V4A?

Hi, it is in and working. Only thing I can't set the bias. Getting 0 V when idle (no load, no signal). I think when I did it the first time with the bought PCB I was able to set it to the 7mV accros one emiter resistor as suggested, but I am not sure I was able to do it.The circuit is identical...

Hi,had it parked for ages but just today I am working on finishing this. I have made the two pcbs one was tested already, the other one not yet. I will post pictures once it's all in and working

Hi. So I did that and it works! Lights light up as they should and relay clicks and music plays. Can I leave it like this with the pins disconnected? Or is there some ic I could replace it with? Almost nothing comes up in google when I search for SVITD62501. Only other option would be to get...

Hi, thanks. I will give it a go. So if those pins are desoldered and IC502 is the culprit (other things ok) I should get relay click and sound out of speakers?

Hi, 13 and 14 are 0, there is 0 volatge on base q512, but there is correct voltage on colector. R552 is good, so is R556 and q512 nad q515. Pins 3 & 4 are good. 0.6 V

Hi,no lights except for the new class a lamp. No on/standby or preheat, bias etc diodes

Hi, thanks for looking. Yes, both are good, connections too. The highlighted lines are areas I checked both parts and connections

Hi, so I have this amp that I fixed (just a busted diode and bias transistor on one channel, and replaced new class A lamp and computer drice lamp with diodes) and sold. The guy took it home (on his motorbike) and did something and now id does not work. He said phono was playing into one...

Hi. Yes! When I put in the replacement pack on one channel it worked. It looks like it needs the output stage for dc to be fine and relay to click. But my own personal story does not end here: I then connected the other channel to my version of pcb with the same circuit as the bought one. And...