Marantz 18 receiver needs help

[bigdrums925]

This repair is a nightmare. Take a look at the driver board schematic. Q1001, Q1003, & Q1005 on the chart are all listed as Marantz # 34-1007.
Yet the schematic shows them as PNP & NPN devices.
One of the driver boards has had these 3 transistors replaced with ECG 234's. PNP's

Marantz has apparently long lost the lists that would tell us what Marantz part number equivalents are, and seemingly their authorized service centers have too.
So I'm not sure if this unit can ever be repaired since no one seems to know what the generic part numbers are or can provide the Marantz numbered parts.
Any one care to offer a suggestion how to solve this screwy mess?

[nickb]

This repair is a nightmare. Take a look at the driver board schematic. Q1001, Q1003, & Q1005 on the chart are all listed as Marantz # 34-1007.
Yet the schematic shows them as PNP & NPN devices.
One of the driver boards has had these 3 transistors replaced with ECG 234's. PNP's

Marantz has apparently long lost the lists that would tell us what Marantz part number equivalents are, and seemingly their authorized service centers have too.
So I'm not sure if this unit can ever be repaired since no one seems to know what the generic part numbers are or can provide the Marantz numbered parts.
Any one care to offer a suggestion how to solve this screwy mess?

1) Do what Juan said "I would redraw driver and current halves on a single sheet and the usual way , so the standard power amp which is hidden in there is recognizable."
2) Measure the DCV on each transistor, annotate the schematic you you drew with this info and then post it.

BTW, If I wasn't getting getting +/-1.4V from the driver I'd be looking at the output stage not the driver.

[bigdrums925]

I will do my best to redraw the driver & output stage together but have no experience doing that so may take some time.

So are you saying that the output stage provides the +/- 1.4v?
I unsoldered that wire and found no voltage coming from the output or the driver board.
Something is very screwy here!

[nickb]

I will do my best to redraw the driver & output stage together but have no experience doing that so may take some time.

So are you saying that the output stage provides the +/- 1.4v?
I unsoldered that wire and found no voltage coming from the output or the driver board.
Something is very screwy here!

I did not know you unsoldered the wire.

The signal comes from the driver board ( actually the voltage amplifier) but the voltage is determined by the base-emitter junction of the the driver transistor (e.g. Q7) and the emitter diode drop (e.g) CR19. If are getting zero drop on one of those that would tell us something is amiss there. If you unsoldered the wire then that changes things as we can no longer be sure what is happening.

Reconnect and measure as requested please.

EDIT: I'll draw up something for you.

[nickb]

Here is a first pass of it drawn in a more logical fashion. Still needs the component refs to be added.

M18-1.pdf


EDIT: ..and now with some errors fixed and component refs. The two driver boards are the same so I didn't put all the refs on the second channel. Added some currents and expected voltages.

M18-5.pdf

[bigdrums925]

WOW nickb that was quick. You must have a program for drawing electrical circuits, no?
I'll look this over and get you the voltages (as many as I can anyway) and post.
Gonna take a little time as I have obligations tonight and tomorrow.
And Thank You!

[nickb]

Yes, I use KiCad as it's free and very good. If you download it I can send you the project and then you can edit it yourself.

I've made some more corrections and fixed the bit about the 1.4V - I forgot abut the triple diodes in the bias cct.

[bigdrums925]

Yes go ahead and send me the latest drawing for KiCad.
Downloading it now

[nickb]

Here is the zip: Model18.zip

[bigdrums925]

While checking for the requested voltages I found the output transistors on the left channel are both shorted.
I may have caused this because the emitter resistor on one of them burnt suddenly, but he other did not.
They have been replaced before and are Motorola MJ21193/MJ21194.
Is there other TO3's that might work in the mene time?
I will order new ones and should have them by 3/19/18
Will post the updated schematic with the measured voltages soon

[bigdrums925]

I have amended the KiCad schematic to show the voltages at the different transistors
I have saved it as "save current sheet only" but I don't see a updated file in that directory.
Should I save it as "save schematic project"?
How can I save it as "Model 18-6?"

[bigdrums925]

So this is my first attempt at amending a schematic in KiCad
See if it works
M18-6.ZIP

[nickb]

Jut print it as a pdf of chose the name at that point. You don't change the name of the project.

[nickb]

So this is my first attempt at amending a schematic in KiCad
See if it works
[ATTACH]47572[/ATTACH]

Please just post the pdf so everyone can read it.

You have conflicting voltages i.e. on several nodes you have two different voltages. Have you at any time adjusted R26 i.e. the bias voltage setting trimmer?

[bigdrums925]

M18-5.pdf

I will re examine the voltages and correct
never have adjusted any trim ports on this unit