Hi all, since i am waiting for a replacement power switch for my 2216b, i am going to start getting into my 2250b So i turned on the 2250b (using a DBT) and it turns on no problem but no sound i did notice that the relay did not switch on, before i start cleaning things up, what are the first steps to see what's going on, I did notice there were no jumpers between the Main and Pre amp so i made up a set yet still no relay turning on. Where do i begin.
Thanks Pat
Thanks Pat
First thing to do is find out why the speaker relay is not switching.
Probably DC on the speaker line. Check around HB05/6/7 if there is no DC on the line.
Probably DC on the speaker line. Check around HB05/6/7 if there is no DC on the line.
Could you use the pre-outs to test for dc offset.
J807-J810 are on the power board, appear to be the in/out of the relay, the schematic is on hifiengine to be sure.
J807-J810 are on the power board, appear to be the in/out of the relay, the schematic is on hifiengine to be sure.
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OK I started to go over this unit i knew there was a problem when i got the unit!! The first thing after checking some of the voltages was to test the output transistors (I took them off and tested them) the right channel was ok the left had both transistor showing there were shorted, I changed them out with new transistors and when i put the unit back on the DBT VERY BRIGHT light, I am trying to determine were to start troubleshooting, were do i begin???
I think i was able to isolate the problem to the left channel, I pulled out the 2 new transistors and turn on the unit and the relay clicked on, some people on the site said that the H701 and R713 have given them problems I do not want to guess but knowing that the problem is in that channel what would be my next step???
Just check if the voltage across H701 is correct. It should be similar to the good channel.
Driver transistors could be favourites if the outputs had failed short circuit.
Driver transistors could be favourites if the outputs had failed short circuit.
Do a quick static resistance check first (amp off) and see if they seem leaky or short.
If they are OK then we short out the bias generator and do voltage checks with the amp running.
If they are OK then we short out the bias generator and do voltage checks with the amp running.
R731 I would not know at this point I will be pulling out H714 and H715 to test them, I guess i will order new ones, only because they will be out why not replace them, and i will keep moving forward from here
Am I to assume that when replacing a component to look for a updated replacement or if possible replace with the same if it is still available???
Some good news i pulled and checked the H714 and 715 the were OK now have to wait for the resistors to get here will keep you posted
R731 is one of the emitter resistors on the driver stage.
The most likely scenario is that the failed output transistor caused the 0.22 ohm emitter resistor to fail open circuit leaving the driver transistor and the 220 ohm to try and deliver all the fault current.
You need to be very very sure these are all OK. If I was repairing this I would look to replacing the drivers and H707 as well using modern parts. The original failure of the output transistor could well be caused by a problem earlier in the amp.
Modern semiconductor replacements mean that the circuit may need tweaking to remain stable against oscillation and instability and also thermally stable.
The most likely scenario is that the failed output transistor caused the 0.22 ohm emitter resistor to fail open circuit leaving the driver transistor and the 220 ohm to try and deliver all the fault current.
You need to be very very sure these are all OK. If I was repairing this I would look to replacing the drivers and H707 as well using modern parts. The original failure of the output transistor could well be caused by a problem earlier in the amp.
Modern semiconductor replacements mean that the circuit may need tweaking to remain stable against oscillation and instability and also thermally stable.
Still waiting for parts but i have a question I want to check the outputs using an Oscope, I have a tecktronics 2232 OS, a Fluke 6070A signal generator, and a HP 8116 function generator, these units was handed down to me from my uncle. My question is what type of connector do i use? I have a bnc to rca but it is not split only 1 rca at the end, so my question is when i plug the bnc into the signal gen. i plug the rca into the aux.how do i read 2 channels or do i have to switch the rca to each right and left every time i what to see each channel. I watch the videos on YT and they can switch from left to right on the OS do they use a bnc cable with 2 rca plugs on the end???