Ok is it normal that the good side has 15.63 on the center pin and I have 33.3 on the center pin on the bad side?
The regulators both feed left and right channels. If one was defective, it would affect both channels.
Look up the datasheets for them and look at the pin configuration.
Look up the datasheets for them and look at the pin configuration.
If the bias isn't working, something has to be different between the two channel.
Did you compare the DC voltages on the various transistors of the two channels?
Did you compare the DC voltages on the various transistors of the two channels?
Yes I checked all of them that are on the MEHSA and Q6,Q7,Q10,Q11 all have:
Left Pin:6.03vdc
Center Pin:10.36vdc
Right Pin: 9.2mvdc
Left Pin:6.03vdc
Center Pin:10.36vdc
Right Pin: 9.2mvdc
Those are the power supply FETs. Like the regulators, if there was a problem there, it would affect both channels.
Are the 0.1 ohm source resistors within tolerance on the bad channel?
If they are, desolder Dx02 and Dx04. Does that let the channel play cleanly?
Are the 0.1 ohm source resistors within tolerance on the bad channel?
If they are, desolder Dx02 and Dx04. Does that let the channel play cleanly?
Perry,
With D202 and D204 removed the channel plays clear and it seams a little louder then the other channel.
I understand that you don't have a scope but for instances where a scope was available, this thread would have stopped about 120 posts back. That's how important having a scope can be.
Reinstall one diode at a time and re-check. For the diode that returns to a distorted output, check the protection circuit transistors that are connected to that diode.
Reinstall one diode at a time and re-check. For the diode that returns to a distorted output, check the protection circuit transistors that are connected to that diode.
Ok Is there a scope that you would reccomend that wont brake the bank? Iam just working on a couple amps trying to lean a little more about them and doing this as a hobby.
The static came back when D204 was re-installed. What diodes would be the protection circuit D206 and D207?
The static came back when D204 was re-installed. What diodes would be the protection circuit D206 and D207?
That's not static. That's the entire bottom half of the waveform being clipped off.
See attached.
Virtually any scope is better than none. You need one that can accurately display about 150kHz square wave, at the very least. I absolutely detest most all LCD scopes and recommend CRT based scopes for audio but trying to convince people to use CRT based scopes is pointless so I won't try.
What's your budget?
See attached.
Virtually any scope is better than none. You need one that can accurately display about 150kHz square wave, at the very least. I absolutely detest most all LCD scopes and recommend CRT based scopes for audio but trying to convince people to use CRT based scopes is pointless so I won't try.
What's your budget?
I dont see anything attached.
What would something that would work go for? I really haven't looked into scopes yet.
You could get a VERY usable scope for about $150 on ebay (don't buy without emailing me links to auctions). You may be able to find something locally, especially if there are any ham-radio type gatherings.
Ok. Are there any particular brands or models to look for?
I tested A couple of the resistors in the boxed area and I think there are 3 or 4 resistors that are bad. Could this be the issue?
I tested A couple of the resistors in the boxed area and I think there are 3 or 4 resistors that are bad. Could this be the issue?
It's unlikely that all are defective. Slide them off to one pad and remeasure.
It's far more likely that a transistor is leaky or shorted.
It's far more likely that a transistor is leaky or shorted.
Tektronix stuff is getting very reasonable, you can find working 475's at hamfests all the time for under $200. I don't like shipping Tek gear though, the CRT's are very fragile. If you must use ebay, get something a bit more rugged like a B&K or something like that. I have a 15mhz B&K on my bench, it's been bulletproof as long as I've had it and it was free from a friend.