Harman kardon 150+ quad low output issue

Johnnyhigh5

Johnnyhigh5

Member
Hello, I'm having problems with the left channel on this receiver. When I start it up the left channel will work for awhile ranging from 2 minutes to a few hours, and the then fade out. Regardless of what input setting. I'm not sure where to start trouble shooting.

It also has very low output sound when it's set to fm or fm stereo. At about half volume you can just make out what song is playing. No distortion. I've cleaned out the switches and pots with no luck.
 
If it's never been rebuilt, it could be a number of things. Bad capacitors for one. Could be a transistor with a heat problem. Can you monitor the power supply voltages as it warms up?
 
I haven't monitored the voltage, but after the channel cut out I checked the voltage from the power caps to the amp. They were the same readings as the right channel.
 
Johnnyhigh5 said:
... I checked the voltage from the power caps to the amp. They were the same readings as the right channel.
Click to expand...
That is a good start. Checking the other power supply voltages is a good next step. It sounds like you are operating this receiver in 2-channel stereo mode. If so, switching to quadraphonic mode, where the front back channels are not bridged, may allow you to discover if the channel fade out is due to one of the four channels fading or something further upstream failing. You certainly have a nice receiver. Good luck with the repairs.
 
Thanks! Great idea to set it to quad instead of stereo 2 channel. I've never tested the back channels. I'll have to test for a few days. So far the rear right channel sounds a little flat and gets static now and then. The left rear channel sounds nice and strong. It's basically the opposite with the front channels. I've had two speakers on the front two channels set to both 4 channel and two channel and the left channel always goes out. I should know soon if both left channels cut out. I'll keep you posted. Thanks!
 
Not sure how similar the 150+ is to a 75+, but on my 75+ the 12 2SC693G transistors in the pre-amp were leaking causing low/distorted volume. Seems it might be a common issue, another AKer had the same issue.
 
Do you remember what you replaced the 2SC693G with? I just checked the manual, and my pre amp has the same transistors.
 
I found the datasheet for the 2SC693G transistor, and typed in the info on mouser.com, and they came up with the KSD261CGTA. Can anyone confirm that this is a good replacement? I'm not familiar with finding good replacement transistors. Yet. Thanks!
 
Hi, I used a KSC1845 Fairchild KSC1845FTA

I ordered 100 of them as they are cheap, and tried to match the hfe for each stage. In mine there were 3 transistors per channel. The signal went thru the 1st transistor, then the tone controls, then the 2nd and 3rd transistors. I matched the hfe on all the 1st, then the 2nd, then the 3rd, just trying to keep the channels balanced.

Here is a thread by Anderslober on the restoration of his 75+, it has some good info, but again, I'm not sure how similarSound fading on Harman 75+ problems. the 75+ and 150+ are. Might have some info that would help.
 
That is good to hear! I have 15 of the KSC1845FTA transistors. Do they need to be hfe balanced? All I have is a volt meter. Can I test with that?
 
Last edited:
So far my plan is to recap the 4 amp boards and replace the transistors previously talked about on the pre amp board. After testing the rear channels since I don't have 4 speakers to test with, I found the rear right to be flat sounding and it had a lot of static and then cut out. The front left still worked after the rear right cut out. Hopefully the recap and transistors being replaced will fix the channel issues.

Not sure where to begin with the fm issue. The tuning meter and tuned in light work, so the issue must be after that?
 
Johnnyhigh5 said:
That is good to hear! I have 15 of the KSC1845FTA transistors. Do they need to be hfe balanced? All I have is a volt meter. Can I test with that?
Click to expand...

I don't know that they really need to be, but I did it just to make sure there wasn't a noticeable difference. You can pick up a cheap meter at Harbor Freight that will measure hfe.

7 Function Digital Multimeter

Probably not the most accurate, but it will get you close.

Johnnyhigh5 said:
So far my plan is to recap the 4 amp boards and replace the transistors previously talked about on the pre amp board. After testing the rear channels since I don't have 4 speakers to test with, I found the rear right to be flat sounding and it had a lot of static and then cut out. The front left still worked after the rear right cut out. Hopefully the recap and transistors being replaced will fix the channel issues.

Not sure where to begin with the fm issue. The tuning meter and tuned in light work, so the issue must be after that?
Click to expand...

The static is most most likely caused by dirty controls, the rotary switches on my 75+ had allot of dust and oxide build up, there is a really good thread on cleaning controls, I thought it was a sticky but can't find it now.
 
Last edited:
Livin4 said:
The static is most most likely caused by dirty controls, the rotary switches on my 75+ had allot of dust and oxide build up, there is a really good thread on cleaning controls, I thought it was a sticky but can't find it now.
Click to expand...

The static was separate from moving any of the controls, and turning all the knobs and switches didn't cause the channels to come back on. I cleaned the switches and pots. I'll try doing it again. I replaced the transistors on the pre amp board with no change. The two channels haven't came on the last time I checked it out. I'm thinking the static in the rear right channel was letting me know it was going out for good. Seems like the problem is in the tone board or the matrix board. Since on two channel I could hear the static from the right rear channel and when the front left cut out it caused the rear left (which is a working channel) it cut out also. Normally, I would move the switch on the back(4 ch/2ch) back and forth a few times which would bring the front left back on for an unknown amount of time. I haven't done that the last few times I tested. I'll clean that switch again thoroughly.

Also, I noticed that my midrange pot does not change as I turn the knob. Maybe that has something to do with it?
 
Update: I recapped the pre amp board and matrix board. All channels sound very good and balanced. The midrange pot is working now. I'm getting static in both right channels. More in the front channel. Regardless of volume. Sometimes it's there from start up. Before the clamps board allows the music to play. I'm thinking it's coming from the amp since the volume doesn't change how loud the static is. I have the schematic. Could a transistor be the problem? Or possibly a filter capacitor? Any help would be appreciated. Thanks!
 
I had the same problem, one channel disappeared and it turned out to be the tape mon.1 switch. I kept pressing it and I had distortion at first then channel came back on nice and clear.
I had cleaned all the switches with dioxit a few months back so will give it another go.
 
You must log in or register to reply here.

Similar threads

R
Harman Kardon 800+ Quad Receiver Treble Issue
Replies
7
Views
1K
RSilverman
R
J
Low Volume From Harman Kardon 630 Twin
Replies
9
Views
3K
Hokieman
Hokieman
E
Harman Kardon CD491 - Left Channel Dead - CANNOT Figure This Out
Replies
0
Views
414
EADGBE
E
runnin'
Harman Kardon HK395i with issues
Replies
7
Views
800
Goldie99
Goldie99
Calvink100
Harman kardon Avr75-static in left channel
Replies
5
Views
385
Calvink100
Calvink100
Back
Top Bottom