Nava [Roland TR-909 replica] Hi-hat and Ride/Crash trigger problem

[belzrebuth]

Hi all,
I've got a problem with a Nava that was built from someone else.
The hi-hats and the ride and crash are slowly rising to full volume when first triggered by the sequencer.
When they reach full volume they respond normally.
The only thing these sounds share is that they're samples triggered from an eprom and that they have identical trigger circuits and very similar analog paths from the eprom to the output.
Hi-hats are reaching full volume faster than the ride and crash but their behavior is similar.

Schematics are here for all the sounds:
https://www.dsl-man.de/display/DSO/Nava+TR-909+Clone?preview=/17236005/17301561/Nava_v1.0l_Schematics.pdf#NavaTR-909Clone-Schematics:

A circuit explanation is here:
http://www.network-909.de/hihatand.htm

So far the only clue I've got is that when I try to measure voltage (essentially putting a very big resistor parallel to the resistor which goes to gnd (say r491 on the hi-hat circuit) the sound completely stops.
Things I've tried:
Replaced the NAND chips and the 4013 ff.
Replaced the 100pF capacitor.
Replaced the actual EPROM on one of these sounds (don't know why just did it in case it did something)
Replaced IC51 (M5218) and C132
Checked q70 on the crash circuit in case it's a fake or malfunctioning..swapped it with the handclap one; clap works fine so q70 is good.
Also replaced the shift register responsible for propagating the trigger pulse from the MCU to the corresponding circuits..
Still nothing..
I'm unsure on how to proceed..
Any ideas would be much appreciated as this is troubling me for quite some time.

[SMdude]

R491 is holding the reset line low, so if the voltmeter causes the reset line to be in its reset state, then it probably won't put out any sound.
For the volume problem you are having, what if you warm up areas of the board and also use some freeze spray. Doing this should help you to quickly identify the area causing you grief.

I think q84 or q52 or the signal that comes from  Accent_HH(I would look at the Accent_HH signal first) or C547 in the DAC multiplexer cct or the 4051 ic111, perhaps has a few channels with poor on resistance vs temp stability. That would also explain the problems you have with the other circuits too. By looking at the voltage of Accent_HH you should be able to tell if the problem is before or after there. It seems that line controls volume and is a quite nifty VCA circuit.

Cheers