Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Messages - g1

Since you already replaced Q2, next suspects would be C7 or Q3.
The link you posted is not working.  Try to attach your picture directly.  When you respond to this post, click the 'preview' button and you will see the option to attach a file.
Quote from: Jesse on May 15, 2024, 02:21:50 PMAny book recommendations for Electronics Repair / Troubleshooting?
Lots of good suggestions in this thread:
Nice work and great name for your project.   :)
Ok, the amp wants CBE then, so the parts are correct type.  If that is true then voltages for T5 in post #42 are impossible. 
The highest voltage for T5 should be at the emitter.
If it's easier for you to call them out as pin 1,2, and 3, that will work as well.
Recheck T5,T4, T6.
Sounds good.  Try it with load.  Some amps have trouble starting up loaded while on the bulb limiter.
If you get a bright bulb when you power it up loaded, you will have to power down, remove load, and power up.  Then (if bulb dim again) connect the load while amp is running.
Yes, any transistors without plastic backs that are mounted on the heatsink need an insulator.
If the Q9 collector was in contact with the heatsink (ground), that probably explains the excess current through Q4 (via R97).
Quote from: Jesse on May 07, 2024, 04:01:33 PMQ9 has fresh thermal paste and seems to be tight to the heatsink.
What about it's insulator?  Don't it and the output transistors that are mounted on the heatsink have mica insulators or similar?
I think you got those R97 and R98 voltages reversed, but voltage across R41 seems normal, and 0V across R98 would be good.
So there seems to be about 50mA current through Q4, which is too much.
Is it possible Q9 is no longer insulated from the heatsink?
Quote from: markorock37 on May 07, 2024, 12:59:57 AMIs it possible the new ones dont have the same pinout as the originals?
Yes it is possible.  Measure resistance from D4 cathode to T5.  One of the T5 pins should read zero ohms to D4 cathode.  Which pin is it, pin 1,2, or 3?
Which T5 pin reads short to R42?
Can you verifiy that R97 is still 100 ohms?
Also measure voltage across R98 when you have the 5V across R97.
And also voltage across R41.
Quote from: saturated on May 04, 2024, 03:18:47 PMPretty funny the book noted "although Vo can be directly measured across A and B it is good practice to make all measurements with respect to ground"
Does Vo mean V offset?  Where measuring direct from A to B should give zero when they are balanced?
Quote from: markorock37 on May 02, 2024, 07:49:32 PMT3 pins 1,2,3=C,B,E
T5 pins 1,2,3=E,B,C
As far as I know, there is no such thing as CBE pinout for these.  But, apparently there are 2 versions of each, and could be either EBC or ECB.
Can you post a link to the exact ones that you bought?
The other thread ended with Q8 catching on fire and no resolution.  It's better if you just tell us what is going on with your amp.

You can monitor the voltage across R97 (one probe at each end).  If you see more than 5VDC, stop.  As you move the variac voltages may jump around so give it a couple seconds to stabilize.
Also keep checking for DC at amp output.
If you are seeing low current on the variac meter, you should be ok to raise the voltage.
see attached