High voltages in Elekit TU8600S

[LeNote]

I was having a similar problem with a 8600R. Worked fine for a year or so, till I suddenly got a hum in the right channel. No voltage on a testpoint at the right ripple filter. It was suggested to replace a mosfet and a zener diode which I did. Also replaced the tubes, as they could have caused the problem in the first place. Got voltage back again, but the hum remained, only at a higher pitch now. Checked all soldering, switched output transformers, replaced another zener diode (which appeared to be fine), resoldered many points on the right channel, all to no avail. Amp is unusable now. Looking at the forum, I'm not the first with this problem, seems to be a weak point with this amp. Any suggestions welcome. Thanks

 

[vkung]

Sent me all test points

 

[LeNote]

 

[vkung]

TU-8600S is very stable amp.
Are you using 12AX7 for the driver. TP1 and TP2 should be 0.8V?
where are you located? I can chat with you via Facetime or Whatapps
I have questions to ask you to locate the problem...Don't worry .. it can fix

 

[LeNote]

It's an 8600R, so spec is 1.15 for TP1 and TP2. Located in EU.

 

[vkung]

TP19 ok
TP 20 not ok
try to swap the 300b to check the voltage of TP 19 and TP20
you need to follow the sechamtic .. to locate the issue
1st make sure it is not the tube set issue ...

 

[LeNote]

Switched 300Bs. TP19 and TP20 measure the same, so tubes are not the problem. When measuring, touching testpoints increases hum. What happened is that hum suddenly disappeared completely until switch of. When switching on again, hum reappears

 

[vkung]

i think you still have damaged components

Your TP28 is ok.. TP20 too low
you need to follow the follow the components around TP 20

 

[LeNote]

Zener diodes, transistor and fet already replaced. Resistors all measure well. I’ll order the 10u450v caps to replace

 

[vkung]

I do not think it is the cap

 

[vkung]

If you cannot locate the issue, you can send the main pcb for repair

 

[LeNote]

Where should I send it and what are the costs? Thx for the info

 

[vkung]

It is not much
Pls send your request to tamura@elekit.co.jp