Fostex early A8 8 track reel to reel will not erase or record

[fireman]

I have put 3 photos in my album but cannot get them to apear in this reply!

one is the schematic that I have drawn out again, the others are the scope shots of the oscillator output before and after removing the two capacitors c20 and c26, the after pic has the scope on 2 v/div so the voltage has risen to around 12v and the waveform is more sine shaped than before.

Whilst removing the caps I did notice that they where both connected in reverse to both the pcb layout in the manual and the silk screen on the pcb, I am thinking that this would make no difference to a 100 kHz signal but will replace them as per the silkscreen.

I also noticed that the resistor r54 which triggers the osc unit is 1 ohm on the parts list for the pcb but the actual resistor is 47 ohm looks to be original with factory looking paint and bend on leg, I'm thinking of changing this to a small pot to see if the value is critical. Not sure if this is a typo on manual or a mistake in production.?

If somebody could move my pics here this post will make much more sense, thanks

[g1]

When posting, click on 'go advanced'
Then scroll down and click 'manage attachments'
A separate box should open called 'manage attachments'
Drag the images from the folder down into the area labelled 'attachments'
Once they appear in there with checkmarks, click on 'insert inline'

[fireman]

Thank you, I had managed to get to the go advanced bit, but I couldn't get the images to move across, I'm on my iPad, the screen scrolls when I try to drag anything, I'll have to get the laptop out and try again.

[olddawg]

Have you tried "tickling" the oscillator circuit with a can of freeze? lol

[fireman]

photos are now attached to previous post, hope it reads better now.

olddawg, no I haven't tried cold spray, I don't have any here, my workshop also doubles up as a dinning table,

though I have had some success in increasing bias level, after disconnecting the two caps on the output of the osc unit to test and getting a small increase measuring at the output terminal I replaced the caps as per silkscreen (polarity) I put a new 1uF in but didn't have a 33uF so had to use the original. I then removed the rec/repro boards and tested at the connector, the rec bias was off the screen of the scope even on 10v/div (screen is 10 wide by 8 high) , so over 80v?
the osc (erase) signal was around 20v, soooooo

thinking..
1 should have used x10 on probe to get a proper reading of rec bias

2 the caps can't have been blocking the signal, it would have been present on osc unit output before.

3 if the signal was leaking to ground though L1 it would still be doing it.

4 the signal looses amplitude when the rec/rep boards are installed, this would make sense as there are multiple paths through the heads to ground.

I measured the dc resistance to ground from the erase head cold term and got 50 ohms but this will be passing a 100khz signal so should be impead or is this splitting hairs?

I put the track cards back in and tried the machine still doesn't erase and still only just records

I'm goinig to try replacing one track card at a time to see if one is loading down the signal, they are all connected in parallel.