Dears,
I am trying to repair this beauty from longer time, in vain.
Main problem is negative voltage close to negative rail on most of the transistors.
The voltages are close like on attached printscr, R30 is added only for simulating such situation, please delete it for LTSpice sims, and connect opt Q12,13.
I desoldered all of the transistors (opt are desoldered as in the sch), checked them, and were OK, I even soldered new ones, in vain.
Please ignore complicated nfb nest, this is just the simplification of Gm selector, it is messy but works for the simulation.
This is how it looks more or less in reality:
I attach also asc file,
Please give a hint what more should I check,
and thank you in advance
regards
Pawel
I am trying to repair this beauty from longer time, in vain.
Main problem is negative voltage close to negative rail on most of the transistors.
The voltages are close like on attached printscr, R30 is added only for simulating such situation, please delete it for LTSpice sims, and connect opt Q12,13.
I desoldered all of the transistors (opt are desoldered as in the sch), checked them, and were OK, I even soldered new ones, in vain.
Please ignore complicated nfb nest, this is just the simplification of Gm selector, it is messy but works for the simulation.
This is how it looks more or less in reality:
I attach also asc file,
Please give a hint what more should I check,
and thank you in advance
regards
Pawel
All you have left are the diodes. DC cap .
Super simple circuit , like the Sonance 260. "Hitachi" topology.
Super simple circuit , like the Sonance 260. "Hitachi" topology.
And each end of R26 and R18?
And what is state of base and emitter of Q13,Q13? And voltage at OUT node? Connected to R26?
And what is state of base and emitter of Q13,Q13? And voltage at OUT node? Connected to R26?
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What is strange, the voltage drop on R7 10k (R722 on original pdf sch) is exactly twice higher than in good chanel
I’m in airplane, so marginal at best. 😁
With output transistors disconnected, there’s no bias feedback path so amp can’t bias into operation. There may not be anything wrong, but risky to reconnect and try. I recommend using a Dim Bulb Tester. You can find them described in the forum. That’s the safest course.
With output transistors disconnected, there’s no bias feedback path so amp can’t bias into operation. There may not be anything wrong, but risky to reconnect and try. I recommend using a Dim Bulb Tester. You can find them described in the forum. That’s the safest course.
Hi Folks,
Thank you for the hints,
More or less I checked them before.
It is clear that Q1 pulls too much current and Q2 too little, but it seems unrelated to semiconductors quality.
I have to dig deeper into physical construction of pcb and related, it looks like electrical issue is caused by mechanical issue.
Regards
Pawel
Thank you for the hints,
More or less I checked them before.
It is clear that Q1 pulls too much current and Q2 too little, but it seems unrelated to semiconductors quality.
I have to dig deeper into physical construction of pcb and related, it looks like electrical issue is caused by mechanical issue.
Regards
Pawel
You were right. Wisdom from above?
After connecting via bulb tester, the bulb shines high and low, so there is another embedded bug.
The voltage at all of opt bases is -0.7V, this means voltage spreader doesn't work properly or the amp consumes more current at start and a 100W bulb is too thin...
Measured voltage drop on R22 fluctuates from 0 to 1.7 as the bulb blinks.
Do you think to take a risk and disconnect the bulb and run up dorect from power socket?